South African Journal of Botany 89 (2013) 244–256
Contents lists available at ScienceDirect
South African Journal of Botany
journal homepage: www.elsevier.com/locate/sajb
Wood anatomy of the tribe Podalyrieae (Fabaceae, Papilionoideae):
Diversity and evolutionary trends
A.V. Stepanova a,b, A.A. Oskolski a,b, P.M. Tilney a, B.-E. Van Wyk a,⁎
a
b
Department of Botany and Plant Biotechnology, University of Johannesburg, P.O. Box 524, Auckland Park 2006, Johannesburg, South Africa
Komarov Botanical Institute of the Russian Academy of Science, Prof. Popov Str. 2, 197376 St. Petersburg, Russia
a r t i c l e
i n f o
Available online 12 September 2013
Edited by JS Boatwright
Keywords:
Fabaceae
Fynbos
Grouped vessels
Helical thickenings
Podalyrieae
Shrubs
Trees
Wood anatomy
a b s t r a c t
Detailed wood anatomical data for 32 species from all nine genera of the tribe Podalyrieae are presented, together
with numerical analyses and the mapping of character states onto the latest available molecular phylogeny. It
was found that trees (Cadia, Calpurnia and Virgilia) have vessels in small isolated groups, whilst fynbos shrubs
(the remaining genera: Amphithalea, Cyclopia, Liparia, Podalyria, Stirtonanthus and Xiphotheca) commonly show
highly grouped narrow vessels (frequently in a dendritic pattern), and helical thickening on the vessel walls.
Comparisons of the main character state changes with the molecular phylogeny of the tribe show that the
wood structure of trees probably represents the basic condition in the tribe; character states present in shrubs
appear to have arisen a few times and very likely represent adaptations to seasonal water stress. In general,
the wood anatomy is congruent with current subtribal and generic delimitations. Fire-survival strategy is
reflected in the rays, with seeders having mostly procumbent cells whilst sprouters have square and upright
cells. The close similarity in wood anatomy between Cadia and Calpurnia is in agreement with the transfer of
Cadia to the Podalyrieae. A remarkable diversity of crystals was found, including prismatic, acicular and navicular
crystals, the last two of which may occur singly or in sheaf-like aggregates.
© 2013 SAAB. Published by Elsevier B.V. All rights reserved.
1. Introduction
The tribe Podalyrieae is subendemic to the Cape Floristic Region of
South Africa, with six of the nine genera confined to the Fynbos biome
with its cold wet winters and dry summers, namely Amphithalea Eckl.
& Zeyh. (42 spp.), Cyclopia Vent. (23 spp.) (Schutte et al., 1995), Liparia
L. (20 spp.), Stirtonanthus B.-E. Van Wyk & A.L. Schutte (3 spp.),
Xiphotheca Eckl. & Zeyh. (10 spp.) and Virgilia Poir. (2 spp.). Podalyria
Willd. has 16 of the 17 species endemic to fynbos (one species extends
into the grassland region of South Africa) (Schutte-Vlok and Van Wyk,
2011); Calpurnia E. Mey. has only one species in the Cape Floristic
Region, whilst the other seven species occur in the summer rainfall
Grassland biome of South Africa, with one [C. aurea (Lam.) Benth.]
extending to tropical east Africa and India (Beaumont et al., 1999);
Cadia Forssk. has one species in tropical Africa and six in Madagascar.
The current tribal and generic classification system (Van Wyk and
Schutte, 1995; Schutte and Van Wyk, 1998; Van Wyk, 2005) was based
on morphological, chemical and cytological evidence, which closely
agreed with later molecular phylogenetic analyses. The molecular
studies showed that Cyclopia forms an isolated group sister to the
⁎ Corresponding author. Tel.: +27 115592412; fax: +27 115592411.
E-mail address: bevanwyk@uj.ac.za (B.-E. Van Wyk).
0254-6299/$ – see front matter © 2013 SAAB. Published by Elsevier B.V. All rights reserved.
http://dx.doi.org/10.1016/j.sajb.2013.07.023
remaining genera (Van der Bank et al., 2002) and that the genus
Cadia, despite its radially symmetrical flowers, should be included in
the tribe (Boatwright et al., 2008). In the current classification system,
Amphithalea and Xiphotheca are placed in the monophyletic subtribe
Xiphothecinae whilst the remaining genera are placed in the paraphyletic subtribe Podalyriinae, the latter shown to comprise three
main clades: Liparia/Podalyria/Stirtonanthus, Calpurnia/Virgilia, and
Cyclopia (Boatwright et al., 2008).
Although it has been shown that wood anatomy is useful in exploring the systematics and evolution of Fabaceae (Baretta-Kuipers, 1981;
Gasson, 2000), such studies have thus far focussed mainly on groups
which consist predominantly of trees. All species of Podalyrieae are
woody plants – mostly shrubs or small trees but ranging from tall
trees to subshrubs and creeping shrublets – but their wood anatomy
has remained largely unknown. Some tree species of Cadia, Virgilia
and Calpurnia have been studied in detail (Gasson, 1994; Fujii et al.,
1994) but data for the remainder of the tribe are limited to the observations by Van Wyk and Schuttte (1995) and Schutte and Van Wyk
(1998), who noted and illustrated the diversity of vessel grouping.
This paper describes, for the first time, the wood anatomy of all
genera of the tribe Podalyrieae, and attempts to relate the diversity
and main discontinuities of wood anatomical characters to the current
state of knowledge regarding the systematics and phylogenetics of the
group.
Table 1
Quantitative wood characters of Podalyrieae.
I
II
III
IV
V
VI
VII
VIII
IX
X
XI
XII
XIII
XIV
Cadia purpurea Ait.
KK 33-10
Calpurnia aurea Baker
KK 39-11
Calpurnia intrusa E. Mey.
BEVW 3249 C
Calpurnia sericea Harv.
KK 35-11
Cyclopia aurescens Kies.
ALS + BEVW 771
Cyclopia burtonii Hofmeyr & E. Phillips
ALS 641
Cyclopia buxifolia (Burm.f.) Kies
ALS 544
Cyclopia genistoides (L.) Sieber ex C. Presl
ALS 615
Cyclopia genistoides
ALS 624
Cyclopia intermedia E. Mey.
ALS 646
Cyclopia intermedia
ALS 647
Cyclopia maculata (Andrews)
KiesALS 636
Cyclopia maculata
ALS 528
Cyclopia plicata Kies
ALS 670a
Cyclopia subternata Vogel
KK 43–11
Liparia hirsuta Moench
JSB 595
Liparia myrtifolia Thunb.
ALS 727a
Liparia racemosa A.L. Schutte
ALS 642a
Liparia splendens (Burm.f.) Bos & de Wit
BEVW 3147
Podalyria calyptrata (Retz.) Willd.
KK 03-10
Podalyria lanceolata Benth.
ALS s.n.
Podalyria myrtifolia D. Dietr.
ALS + BEVW 166
24 ± 1.3
12–38
35 ± 1.5
18–48
41 ± 2.7
11–61
45 ± 2.6
18–74
8 ± 0.3
3–18
13 ± 0.5
4–31
19 ± 0.8
5–44
12 ± 0.7
6–22
16 ± 1.7
7–30
18 ± 1.4
7–36
11 ± 0.5
3–39
18 ± 1.2
6–34a
31 ± 2.8
8–60
7 ± 0.4
3–22
23 ± 2.1
10–48
19 ± 1.0
11–33
22 ± 1.5
10–44
25 ± 1.0
16–42
16 ± 1.0
9–28
47 ± 2.5
22–78
26 ± 2.3
8–61
21 ± 1.2
12–36
145
119–165
73
60–91
44
23–63
75
49–102
792
706–877
658
486–788
228
110–411
411
199–575
418
308–610
390
240–637
503
226–706
247
192–329
143
121–170
1615
1322–2144
470
384–555
280
158–356
545
412–688
358
265–574
433
229–593
7156–84
2.0
7
22.0
11
12.5
1.8
10
29.8
1.8
5
31.0
160.5
461
0
476
0
81.2
407
0.1
14.2
40
0
29.6
84
0.1
44.8
122
0.2
118.8
496
0.1
61.6
287
0.5
4.6
18
5.0
a
a
a
504 ± 19.7
290–740
601 ± 21.5
279–807
577 ± 17.3
396–828
453 ± 18.5
269–760
63 ± 15.3
448–817
53216.4
329–673
601 ± 19.8
262–814
709 ± 24.1
422–1019
537 ± 22.9
226–801
751 ± 34.2
424–1064
654 ± 32.7
300–1181
602 ± 15.8
442–810
719 ± 22.8
557–866
542 ± 17.8
346–714
744 ± 21.1
512–983
495 ± 14.3
367–611
411 ± 37.3
135–767
605 ± 17.5
456–821
757 ± 17.4
625–952
602 ± 17.4
381–783
841 ± 23.3
654–1085
511 ± 16.0343–678
18 ± 0.8
12–31
27 ± 1.4
14–43
24 ± 1.3
14–41
22 ± 0.9
11–32
56 ± 2.2
138.2
128 ± 4.3
79–178
191 ± 8.0
102–287
151 ± 4.5
95–214
150 ± 4.5
106–204
228 ± 6.1
164–323
172 ± 7.0
87–245
227 ± 8.5
132–347
322 ± 13.2
165–483
245 ± 11.6
148–393
278 ± 12.7
158–405
174 ± 8.5
97–298
207 ± 9.0
12–5324
167 ± 6.6
109–232
161 ± 5.5
102–232
249 ± 11.3
154–425
217 ± 7.1
159–313
191 ± 6.5
115–266
224 ± 7.5
131–323
198 ± 6.8
125–269
216 ± 9.3
94–306
271 ± 11.1
177–404
161 ± 7.6
80–257
3.9
2.5
3.9
2.8–5.8
3.9
2.7–5.3
5.7
4.4–6.7
4.9
3.8–5.9
5.4
4.0–7.8
4.5
3.6–5.7
5.1
4.0–7.3
5.4
4.0–7.8
4.9
3.6–6.5
5.0
3.7–6.6
4.5
3.4–5.8
5.0
4.0–7.2
5.1
4.1–8.2
4.2
3.2–5.6
5.1
3.1–6.8
6.0
4.6–11.6
4.0
2.7–4.9
5.6
4.1–7.1
6.7
4.8–8.9
5.2
4.2–6.3
5.4
4.2–7.2
5.1
3.8–6.8
135 ± 6.7
83–244
217 ± 12.9
105–396
216 ± 14.7
107–476
225 ± 30.8
88–875
798 ± 67.3
238–v
377 ± 27.9
141–879
282 ± 25.0
121–635
605 ± 77.7
137–1421
331 ± 18.7
145–577
729 ± 76.2
267–1887
453 ± 37.2
178–923
418 ± 22.8
239–765
311 ± 27.7
116–759
227 ± 18.2
73–429
375 ± 27.6
173–771
233 ± 15.7
128–456
456 ± 51.602
160–13
304 ± 26.9
146–656
475 ± 38.6
106–1182
259 ± 19.6
84–687
257 ± 15.5
123–415
314 ± 29.4
158–515
3.7
2.1–6.3
8.7
6.3–11.6
7.8
5.3–11.6
5.8
3.2–8.4
2.9
1.1–5.3
4.6
3.2–7.4
3.7
0–6.3
1.6
0.0–4.2
2.6
1.1–4.2
6.5
5.3–7.4
7.3
5.3–12.6
4.7
3.2–7.4
4.5
4.2–5.3
4.8
3.2–6.3
4.5
3.2–6.3
4.9
3.2–7.4
4.5
3.2–6.3
5.4 ± 0.4
3.2–7.4
4.0 ± 0.2
1.9–5.6
4.9
3.2–6.3
5.1
3.2–6.3
4.83.2–6.3
5.2
3.2–7.4
2.4
1.1–4.2
1.9
0.0–3.2
3.4
0.0–8.4
4.2
2.1–6.3
2.7
1.1–5.3
4.4
2.1–6.3
7.2
4.2–9.5
4.2
3.2–6.3
1.2
0–3.2
3.3
2.1–5.3
3.3
1.1–5.3
3.2
2.1–6.3
6.5
4.2–9.5
3.8
1.1–6.3
3.1
1.1–5.3
2.6
1.1–5.3
1.5 ± 0.3
0.0–3.2
7.2 ± 0.3
4.6–10.2
3.4
1.1–5.3
1.7
0.0–4.2
2.51.1–6.3
8.9
5.3–12.6
11.2
9.5–12.6
9.7
7.4–12.6
9.2
5.3–12.6
7.1
5.3–9.5
7.4
6.3–8.4
8.1
5.3–10.5
8.8
5.3–11.6
6.8
5.3–10.5
7.7
6.3–8.4
10.5
8.4–14.7
8.0
6.3–9.5
7.7
6.3–10.5
11.4
9.5–13.7
8.3
6.3–10.5
8.0
6.3–9.5
7.1
5.3–8.4
6.9
5.3–9.5
11.2
9.3–13.9
8.3
5.3–10.5
6.7
5.3–8.4
7.45.3–9.5
199
164–235
2250
200–26
–
–
–
102.4
277
0.04
5.4
29
7.4
15.7
84
1.0
18.9
78
1.0
8.0
44
4.0
2.1
7
20.0
11.7
54
16.7
3.0
26
13.0
3.2
3.8
3.0
2.8
39–80
3.1
2.6
2.2
2.2
2.7
3.8
2.9
4.3
3.4
3.0
2.2
2.7
3.8
2.8
3.1
3.2
51 ± 2.2
29–73
24 ± 0.7
16–31
36 ± 1.2
29–52
88 ± 10.6
38–320
42 ± 1.6
27–59
44 ± 1.3
33–59
40 ± 3.0
19–90
34 ± 1.5
2–48
46 ± 2.2
27–86
34 ± 1.2
24–49
44 ± 1.7
18–62
34 ± 1.7
19–58
52 ± 2.6
29–87
36 ± 1.6
22–71
44 ± 1.6
26–60
32 ± 1.1
22–45
25 ± 0.8
15–31
A.V. Stepanova et al. / South African Journal of Botany 89 (2013) 244–256
Species and voucher specimens (all in JRAU)
(continued on next page)
245
246
Table 1 (continued)
I
II
III
IV
V
VI
VII
VIII
IX
X
XI
XII
XIII
XIV
Podalyria rotundifolia (P.J. Bergius) A.L. Schutte
ALS s.n.
Stirtonanthus insignis (Compton) B.-E.van
Wyk & A.L. Schutte
BEVW 3331
Stirtonanthus taylorianus (L. Bolus) B.–E.van
Wyk & A.L. Schutte
BEVW 3169
Virgilia divaricata Adamson
AO 16-09
Virgilia divaricata
KK 02-10
Virgilia oroboides subsp. oroboides (P.J. Bergius)
T.M. Salter
BEVW 5722
Virgilia oroboides subsp. ferruginea B.-E.van Wyk
KK 44-11
Amphithalea ericifolia (L.) Eckl. & Zeyh.
ALS 617
Amphithalea rostrata A.L. Schutte & B.-E.van Wyk
ALS 629
Amphitalea vlokii (A.L. Schutte & B.–E.van Wyk)
A.L. Schutte
ALS 743
Xiphotheca canescens (Thunb.) A.L. Schutte &
B.-E.van Wyk
ALS 595a
Xiphotheca elliptica (DC.) A.L. Schutte &
B.-E.van Wyk
ALS 600
Xiphotheca phylicoides A.L. Schutte &
B.–E.van Wyk
ALS 648
Xiphotheca tecta A.L. Schutte & B.–E.van Wyk
ALS 597
25 ± 2.1
10–48
18 ± 1.3
40
13–59
159
3.9
10
16.0
44
6.2
189 ± 7.3
108–273
169 ± 8.1
660 ± 21.0
414–846
438 ± 17.7
3.5
4.5
5.4
3.5–8.5
4.2
2.6
30 ± 1.2
16–42
24 ± 1.0
286 ± 20.6
107–607
342 ± 34.9
6.7
3.2–9.5
3.6
3.1
1.1–5.3
3.4
9.8
6.3–13.7
6.9
6–36
16 ± 1.7
97–207
317
17.7
89
1.0
3.6–5
5.8
85–267
350 ± 13.5
254–663
701 ± 27.1
2.0
14–33
25 ± 1.2
102–658
181 ± 9.2
2.1–6.3
4.6
2.1–5.3
3.4
5.3–8.4
8.0
4–47
74 ± 3.1
39–108
69 ± 3.2
35–98
85 ± 3.9
286–367
18
15–20
17
4–19
18
1.5
5
40.2
1.5
5
44.7
1.5
5
39.5
4.4–7.8
5.8
4.4–8.2
6.4
5.0–8.1
7.3
228–512
291 ± 10.3
194–410
321 ± 9.8
229–484
288 ± 11.5
457–1025
636 ± 35.2
306–1016
615 ± 39.4
375–1088
995 ± 40.8
16–39
28 ± 0.7
20–35
27 ± 0.9
16–36
31 ± 0.9
87–325
244 ± 13.6
130–404
275 ± 22.4
136–572
386 ± 36.6
1.1–6.3
4.8
3.2–7.4
2.3
1.1–4.2
4.7
2.1–5.3
2.2
0–4.2
2.4
0.0–4.2
2.3
5.3–10.5
7.1
5.3–10.5
4.7
3.2–6.3
7.1
49–130
80 ± 3.6
37–121
14 ± 0.9
6–26
10 ± 0.7
5–18
13 ± 1.3
13–21
18
15–21
294
240–333
295
263–374
104
1.5
6
38.4
2.3
18
23.0
3
19
16.0
2.8
17
23.0
5.2–10.4
6.2
4.6–8.7
3.8
2.9–5.1
5.0
3.2–7.7
2.5
153–406
274 ± 13.3
120–424
176 ± 7.6
118–265
175 ± 7.5
84–258
135 ± 5.3
586–1314
813 ± 30.9
367–1114
430 ± 13.8
258–586
546 ± 20.9
256–815
572 ± 13.7
4.2
22–44
30 ± 0.9
20–38
29 ± 1.0
16–40
20 ± 1.0
12–32
22 ± 0.8
198–1060
310 ± 19.8
121–537
237 ± 20.8
78–602
242 ± 24.5
98–616
276 ± 20.5
2.1–6.3
2.8
1.1–5.3
4.9
3.7–6.5
4.4
2.1–8.4
6.2
1.1–3.2
2.3
0 – 4.2
5.6
3.7–8.4
8.6
4.2–13.7
5.2
5.3–9.5
5.2
4.2–6.3
10.6
8.4–13.0
13.1
11.6–15.8
11.4
4–34
16 ± 1.1
67–163
281
15.9
174
13.8
1.4–4.1
4.8
74–187
193 ± 8.6
458–704
517 ± 15.4
2.7
16–37
27 ± 0.9
117–511
33 ± 21.5
3.2–8.4
3.6
2.1–9.5
3.4
9.5–12.6
7.1
6–27
17 ± 1.7
254.5–334.6
134
14.6
38
2.3
3.9–6.1
5.3
121–300
205 ± 9.0
348–678
576 ± 20.6
2.8
16–40
32 ± 1.5
162–564
336 ± 19.2
1.1–6.3
4.7
0.0–10.5
3.8
5.3–1.6
8.6
8–40
13 ± 1.0
124–154
275
16.1
51
20.0
4.0–7.0
5.0
111–345
160 ± 10.5
335–813
421 ± 11.0
2.6
21–52
31 ± 1.1
157–650
230 ± 15.9
2.8–6.5
2.6
1.9–6.5
8.6
7.4–10.2
11.2
4–16
18 ± 1.6
6–35
259–303
415
314–581
16.4
120
2.0
3.6–6.3
6.7
5.3–8.1
112–445
158 ± 6.1
93–229
344–571
590 ± 16.1
394–764
20–44
29 ± 0.7
22–38
103–513
336 ± 26.2
39–670
0.9–3.7
3.8
2.1–6.3
6.5–10.2
5.1
3.2–7.4
8.4–13.0
8.9
6.3–10.5
Legend:
I — Tangential diameter of vessels, μm.
II — Number of vessel lumina per mm2.
III — Mean number of vessel lumina per group.
IV — Max number of vessel lumina per group.
V — Percent of solitary vessels.
VI —Intervessel pit diameter, μm.
VII — Length of vessel elements, μm.
VIII — Length of fibres, μm.
IX — F/V ratio (Fibre length/Vessel element length ratio).
X — Width of multiseriate rays, μm.
XI — Height of multiseriate rays, μm.
XII — Number of multiseriate rays per mm.
XIII — Number of uniseriate rays per mm.
XIV — Total number of rays per mm.
a
In Сyclopia plicata all vessels are united in one group.
2.2
1.9
3.5
3
2.4
3.1
3.7
A.V. Stepanova et al. / South African Journal of Botany 89 (2013) 244–256
Species and voucher specimens (all in JRAU)
A.V. Stepanova et al. / South African Journal of Botany 89 (2013) 244–256
2. Material and methods
We studied the wood anatomy of all nine genera of Podalyrieae, with
a representative sample between one and nine species of each genus.
The source of material was the collection of FAA-fixed samples, housed
in the herbarium of the Department of Botany and Plant Biotechnology
at the University of Johannesburg. As shown in Table 1, each sample
has a voucher specimen (in the UJ Herbarium, acronym JRAU), collected
by A.-L. Schutte (ALS), A.A. Oskolski (AO), A.V. Stepanova (AS), B.-E. van
Wyk (BEVW), JSB (J.S. Boatwright) and E.L. Kotina (KK). The taxa studied, collection numbers, and stem diameters are shown in the Results
section (in the generic descriptions of the wood anatomy and also in
the summary of the results in Table 1). The age of the woody stems or
shoots was no less than three years, with diameters ranging from 4 to
55 mm. Transverse, radial, and tangential sections were made on freezing (shoots with a small diameter) or rotary microtomes (Ernst Leitz
247
GMBH, Wetzlar, Germany and Jung AG Heidelberg, Germany), and
then stained with a 1:1 alcian blue/safranin mixture (Jansen et al.,
2004). Macerations were made using Jeffrey's solution (Johansen,
1940). Where necessary, the wood was softened in ethylenediamine
(Carlquist, 1982) followed by soaking in 15% glycerol in ethanol or boiling in 10% glycerol solution (Jansen et al., 1998). The ethylenediamine
method for softening very hard woods was first used by Kukachka
(1977) and also by Maclachlan and Gasson (2010) but we followed
the protocol of Carlquist (1982). The descriptive terminology used is
in accordance with that of the IAWA Committee (1989).
A special method was used for counting the number of vessels in
wood with a dendritic pattern of vessel arrangement. Since the groups
are often very large whilst the vessels are very small, it is difficult to
count the number of vessels per group. For every sample, we chose
five groups of vessels, measured their size and then counted the number
of vessels in each group. The mean ratio of vessel number per unit area
Fig. 1. Wood porosity and vessel arrangement, LM, TS. (A) diffuse-porous wood, vessels solitary and in radial multiples, Calpurnia sericea; (B) diffuse-porous wood, vessels in clusters,
Cyclopia maculata; (C) diffuse-porous wood, tangential multiples at the beginning of growth ring, Podalyria myrtifolia; (D) semi-ring-porous wood (weakly so), vessels in a dendritic pattern, Cyclopia plicata; (E) diffuse-porous wood, vessels in a dendritic pattern, Liparia racemosa. Scale bars: 200 μm.
248
A.V. Stepanova et al. / South African Journal of Botany 89 (2013) 244–256
of the group was then calculated. Using this ratio, we determined the
vessel number of 30 groups for each of the samples. Standard methods
were used (IAWA Committee, 1989) for all other parameters.
Measurements and photographs were made, respectively, with
an Olympus ColorView Soft Imaging System (Olympus Soft Imaging Solutions, Stream Essentials version 1.8). Crystals were studied under
polarised light. Scanning electron microscope (SEM) observations and
photographs were made on a Tescan Vega TC SEM. Samples for SEM
study were first preserved in 96% ethanol and then dried in an Edward
Tissue Dryer (ETD 4).
Evolutionary pathways for wood anatomical features were reconstructed by mapping their character states on a subsample of one of
the 140 equally most parsimonious trees from the combined molecular
analysis of ITS and rbcL data for Podalyrieae taken from Boatwright et al.
(2008). Character optimisation along tree branches was visualised
using the parsimony reconstruction method with the “Character History
Tracing” option in the computer package Mesquite 2.0 (Maddison and
Maddison, 2007).
3. Results
3.1. General wood description
Wood mainly diffuse-porous (Fig. 1A–C, F). Semi-ring porosity
was observed in some species of Cyclopia (Fig. 1D). Growth rings commonly distinct to faint or absent in two species of Podalyria, some species of Cyclopia, and some specimens of Virgilia, Liparia splendens and
Amphithalea ericifolia. Width of growth rings commonly 0.4–1 mm in
Fig. 2. Vessels characters. (A) Vessels with simple perforation plates and spiral thickening, Cyclopia plicata, LM, RS; (B) spiral thickening, Amphithalea rostrata, SEM; (C) vestured intervessel
pits with scanty vestures located at edge of inner aperture viewed from the outside, appearing as simple rounded and weakly branched warts, Cyclopia buxifolia, SEM; (D) vestured
intervessel pits with numerous vestures varying from simple and unforked warts to strongly branched fine protuberances viewing from the outside, Calpurnia sericea, SEM; (E) vestured
intervessel pits with numerous seemingly unbranched vestures near inner pit apertures viewed from the outside, Virgilia oroboides subsp. oroboides, SEM; (F) deposits inside vessels,
Xiphotheca canescens, LM, TS; (G) deposit inside vessels, Virgilia oroboides subsp. oroboides, LM, RS. Scale bars: 100 μm (A, F), 20 μm (B), 5 μm (C, D), 10 μm (E), 200 μm (G).
A.V. Stepanova et al. / South African Journal of Botany 89 (2013) 244–256
249
Fig. 3. Fibre wall thickness and axial parenchyma distribution, LM, TS. (A) Thin- to thick-walled fibres, Stirtonanthus taylorianus; (B) very thick-walled fibres, Stirtonanthus insignis;
(C) gelatinous fibres, Podalyria rotundifolia; (D) axial parenchyma scanty paratracheal, Cadia purpurea; (E), axial parenchyma scanty paratracheal and marginal, (also vasicentric and in
narrow bands), Amphithalea rostrata; (F) axial parenchyma confluent, Calpurnia intrusa. Scale bars: 50 μm (A–C), 100 μm (D), 200 μm (E, F).
shrubs and 1.4–2.5 mm in trees. Boundaries of growth rings may be
marked by rows of flattened fibres or flattened vascular tracheids and/
or narrow vessels (in species with very thick-walled fibres) and/or by
marginal parenchyma. Vessels narrow, round to angular in outline, relatively rare (Fig. 1A) to very numerous (Fig. 1D, F), commonly in dendritic pattern (Fig. 1D, F), less often in radial and oblique multiples
and clusters (Fig. 1A, B), or in tangential multiples in Podalyria, Virgilia
and Xiphotheca (Fig. 1C). Perforation plates simple (Fig. 2A), intervessel pits alternate, vestured, 3–8 μm in diameter (up to 10 in Virgilia
spp.), round and oval to polygonal with narrow oval to slit-like
apertures (Fig. 2C–E). Vessel-ray pits similar to intervessel ones in size
and shape. Helical thickenings in vessels absent in large trees (Cadia,
Calpurnia and Virgilia) and in two shrubby species (Amphithalea rostrata
and Liparia splendens), but present in almost all species of shrubby genera (Fig. 2A, B), occurring throughout the bodies of the vessel elements
of all diameters (and not only in the tails). Brown to yellowish-brown
deposit (Figs. 1C, 2F, J) in vessels, vascular tracheids and adjacent parenchyma cells in all genera examined except Stirtonanthus. Vascular
tracheids commonly present, more or less numerous in woods with
dendritic pattern of vessel arrangement and rare in woods with isolated
vessel groups. Fibres nonseptate, thin- to thick-walled (Fig. 3A) or very
thick-walled (Fig. 3B, E), with small simple pits, more common on the
radial walls; thin- to thick-walled fibres often gelatinous (Fig. 3C).
Axial parenchyma scanty paratracheal to vasicentric, rarely confluent
(Fig. 3D–F), often also in narrow bands of 1–6 cells wide (Fig. 3E), sometimes marginal, fusiform (Fig. 4C), and in 2, sometimes up to 4 cells per
strand (Fig. 4A). Rays commonly 1 or 2- or 1–3-seriate (Fig. 4B–E), rarely broader (up to 6), 1–6 times higher than axial parenchyma strands,
composed of procumbent, square and upright cells, perforated ray
cells often present (Fig. 4F). Prismatic crystals occur in ray cells in
some species of Calpurnia and Amphithalea (Fig. 5A, B); navicular crystals, often aggregated (Fig. 5C) and crystal sand common for two species
250
A.V. Stepanova et al. / South African Journal of Botany 89 (2013) 244–256
Fig. 4. Axial parenchyma strands and rays. (A) Axial parenchyma strand of 4 cells, Podalyria lanceolata, LM, TLS; (B) axial parenchyma in 2 or 3 cells per strand and 2 or 3-seriate rays,
Calpurnia intrusa, LM, TLS; (C) fusiform axial parenchyma cells, Xiphotheca canescens, LM, TLS; (D) 1 or 2-seriate rays, Virgilia oroboides subsp. ferruginea, LM, TLS; (E) 1 or 2-seriate
rays, Cyclopia buxifolia, LM, TLS; (F) perforated ray cell, Stirtonanthus taylorianus, LM, RLS. Scale bars: 50 μm (A, C, F), 100 μm (B), 200 μm (D, E).
of Amphithalea; acicular crystals in sheaf-like aggregates present in
almost all species of Cyclopia and Virgilia (Fig. 5D, E), and also in one species of Calpurnia. Silica bodies commonly occur in rays and axial parenchyma cells (Fig. 5F) in almost all genera, but their presence often varies
within genera. They are small (up to 3 μm in diameter), spheroidal and
yellowish, and usually solitary. Storied structures were not found.
thickenings not found. Vascular tracheids rarely occur. Fibres very
thick-walled. Axial parenchyma fusiform and in strands of 2 cells, scanty
paratracheal, in solitary strands near vessels, and sometimes diffuse.
Rays 1- or 2-seriate, formed mostly by procumbent and square cells;
sometimes with 1 or 2 marginal rows of upright cells. Crystals not observed. Silica bodies in ray and axial parenchyma cells. Brown deposits
in a few vessels.
3.2. Generic wood descriptions
3.2.1. Cadia
Material studied: C. purpurea Ait. (KK 33–10, 15 mm).
Wood diffuse-porous. Growth rings indistinct, marked by 1–3 layers
of radially flattened fibres. Vessels narrow, very thick-walled, rounded
in outline, solitary and in short radial multiples of 2–7. Intervessel pits
alternate, vestured, with abundant seemingly unbranched vestures filling the pit chambers. Vessel-ray pits with distinct borders. Helical
3.2.2. Calpurnia
Material studied: C. aurea Baker (KK 39–11, 22 mm), C. intrusa
E. Mey. (BEVW 3249 C, 22 mm), C. sericea Harv. (KK 35–11, 16 mm).
Wood diffuse-porous. Growth rings absent in C. intrusa, or distinct,
marked by flattened latewood fibres and commonly also by marginal
axial parenchyma. Vessels narrow, rounded and angular in outline,
solitary and in radial multiples of 2–6. Intervessel pits alternate, vestured, in C. sericea with rather numerous vestures, adjacent to the
A.V. Stepanova et al. / South African Journal of Botany 89 (2013) 244–256
251
Fig. 5. Inclusions, SEM. (A) Prismatic crystals in ray cells, Calpurnia aurea; (B), starch grains and very small prismatic crystals in ray cell, Amphithalea rostrata; (C) navicular crystals in aggregates in ray cell, Amphithalea rostrata; (D) acicular crystals in sheaf-like aggregates in ray cell, Cyclopia aurescens; (E) acicular crystals in sheaf-like aggregates in vessel, Virgilia oroboides
subsp. oroboides; (F) silica body in ray cell, Cyclopia aurescens. Scale bars: 10 μm (A, B, D, F), 2 μm (C), 50 μm (E).
inner pit apertures, varying from simple and unforked warts to strongly
branched fine protuberances (vestures in C. aurea and C. intrusa were
not examined by SEM). Vessel-ray pits with distinct borders. Helical
thickenings not found. Vascular tracheids rare. Fibres very thickwalled (C. intrusa) or thin- to thick-walled. Axial parenchyma fusiform
or in strands of 2 or 3 cells (C. sericea), or of (2–)3–4(−5) cells (C.
aurea and C. intrusa). Axial parenchyma scanty paratracheal, in incomplete uniseriate sheaths near vessels (C. aurea and C. sericea), or
vasicentric, sometimes aliform to confluent (C. intrusa), and also banded
in 2–8-seriate tangential bands (in C. aurea and C. introsa also in marginal bands). Rays are 1–2(3)-seriate (C. sericea) or 1–3(4)–seriate.
Multiseriate rays mostly of square and upright cells with few procumbent cells scattered throughout (C. aurea and C. sericea), or mostly of
procumbent cells with 1 or 2 marginal rows and incomplete sheaths
of square and upright cells (C. intrusa). Prismatic crystals in ray cells of
C. aurea and C. sericea. Аcicular crystals in sheaf-like aggregates in vessels and parenchyma cells of C. intrusa. Silica bodies in ray and axial
parenchyma cells of C. intrusa. Brown deposits in vessels rarely in C.
intrusa and C. sericea.
3.2.3. Cyclopia
Material studied: C. aurescens Kies. (ALS + BEVW 771, 9 mm),
C. burtonii Hofmeyr & E. Phillips (ALS 641, 10 mm), C. buxifolia
(Burm.f.) Kies (ALS 544, 10 mm), C. genistoides (L.) Sieber ex C. Presl
(ALS 615, 7 mm; ALS 624, 10 mm), C. intermedia E. Mey. (ALS 646,
6 mm; ALS 647, 10 mm), C. maculata (Andrews) Kies (ALS 636,
9 mm; ALS 528, 14 mm), C. plicata Kies (ALS 670, 14 mm), C. subternata
Vogel (KK 43–11, 22 mm).
Wood semi-ring-porous (at least weakly so) in C. plicata, C. aurescens
and C. buxifolia, or diffuse-porous. Growth rings absent (C. maculata
and C. subternata), distinct (C. aurescens, C. burtonii, C. buxifolia and
C. plicata) or inistinct, marked by 1 or 2 rows of flattened latewood
fibres, narrow vessels and vascular tracheids, tangentially extended
groups of vessels and vascular tracheids in some species (C. aurescens,
252
A.V. Stepanova et al. / South African Journal of Botany 89 (2013) 244–256
C. buxifolia and C. plicata) form more or less distinct rings of wider earlywood vessels; commonly growth ring boundaries also marked by
marginal axial parenchyma. Vessels narrow (5–50 μm in diameter)
and numerous (N125 per mm2), in clusters and radial multiples arranged in diagonal rows (C. maculata [AL 528]), or mostly in large
groups (N10 vessels) arranged in diagonal to dendritic pattern, or
in continuous dendritic aggregations (C. plicata) or diagonal bands
(C. subternata) with co-occurrence of a few solitary vessels (no solitary
vessels found in C. aurescens, C. genistoides [AL 615], and C. plicata) and
groups of 2–8 vessels. Intervessel pits alternate, vestured, with scanty
vestures located at edge of inner aperture, appearing as simple rounded
(C. burtoni, C. intermedia and C. subternata) and also weakly branched
(C. buxifolia and C. genistoides) warts (vestures in C. aurescens, C. maculata
and C. plicata not examined by SEM). Vessel-ray pits with distinct
(C. burtonii) or reduced borders. Helical thickenings present. Vascular
tracheids common. Fibres thin- to thick-walled in C. maculata, very
thick-walled in other species. Axial parenchyma fusiform (C. plicata)
or also in strands of 2 cells (up to 3 cells in C. aurescens and C. maculata
[AL 636]), vasicentric (C. intermedia, C. plicata and C. subternata) or
scanty paratracheal (mostly as incomplete sheaths near vessel groups),
also in 1–3-seriate tangential (sometimes marginal) bands (up to 5seriate in C. burtonii, up to 7-seriate in C. aurescens and C. gentionoides,
up to 12-seriate in C. plicata). Rays 1–2(3)-seriate (C. buxifolia and
C. genistoides) or 1–3 (4)-seriate (up to 5-seriate in C. burtonii and
C. maculata [AL 636]), composed mostly of procumbent cells (C. burtonii,
C. maculata, C. plicata and C. subternata) with square and upright cells in
few (up to 5 in C. maculata) marginal rows and in incomplete sheaths
(C. maculata and C. plicata), or mostly of square cells with procumbent
and upright cells mixed throughout. Acicular crystals in sheaf-like aggregates in vessels and ray cells in all species examined except C. plicata.
Small bands of acicular crystals in intervessel pits in C. intermedia. Silica
bodies in ray and axial parenchyma cells. Yellowish-brown deposits
common in vessels of C. intermedia, rare in C. maculata and C. subternata.
3.2.4. Liparia
Material studied: L. hirsuta Moench (JSB 595, 13 mm), L. myrtifolia
Thunb. (ALS 727, 12 mm), L. racemosa A.L. Schutte (ALS 642, 19 mm),
L. splendens (Burm.f.) Bos & de Wit (BEVW 3147, 11 mm).
Wood diffuse-porous. Growth rings absent (L. splendens), indistinct
(L. myrtifolia) to distinct (L. hirsuta and L. racemosa), marked by flattened latewood fibres, and also by tangentially extended groups of vessels and vascular tracheids in earlywood, and by difference in vessel
diameter between late- and earlywood (L. hirsuta and L. racemosa).
Vessels narrow, rounded and angular in outline, mostly in radial multiples and clusters (L. splendens), or in nearly continuous diagonal bands
and dendritic patterns, rarely solitary and in small clusters. Intervessel
pits alternate, vestured, in L. splendens with scanty vestures at edge
of inner aperture, appearing as simple warts (vestures in L. hirsuta,
L. myrtifolia and L. racemosa not examined by SEM). Vessel-ray pits
with reduced borders. Helical thickenings absent (L. splendens) or
present. Vascular tracheids common. Fibres thin- to thick-walled.
Axial parenchyma commonly fusiform, rarely in strands of 2 cells, scanty paratracheal, in incomplete sheaths near vessel groups, and also in
2–6-seriate tangential bands (L. splendens). Rays 1 or 2-seriate, of square
and upright cells with few procumbent cells (L. splendens), or 1–3(4)seriate (up to 5-seriate in L. racemosa), with predominance of procumbent cells in both multi- and uniseriate rays; square and upright cells
in 1 or 2 marginal rows and occasionally as solitary sheath cells. Crystals
not observed. Silica bodies in ray cells. Brown deposits in a few vessels of
L. myrtifolia.
3.2.5. Podalyria
Material studied: P. calyptrata (Retz.) Willd. (KK 03–10, 22 mm),
P. lanceolata Benth. (ALS s.n., 23 mm), P. myrtifolia D. Dietr. (AS + BEVW
166, 7 mm), P. rotundifolia (P.J. Bergius) A.L. Schutte (ALS s.n., 24 mm).
Wood diffuse-porous. Growth rings absent (P. calyptrata and
P. rotundifolia), or distinct, marked by flattened latewood fibres, 2–4seriate bands of marginal axial parenchyma, and by difference in vessel
diameter between late- and earlywood. Vessels narrow to moderately
wide, rounded in outline, solitary and in clusters and radial multiples
of 2–10, tending to form diagonal to dendritic arrangement most
distinctive in P. lanceolata and P. myrtifolia. Intervessel pits alternate,
vestured, in P. rotundifolia with scanty vestures located at edge of
inner aperture, appearing as flattened weakly branched protuberances
(vestures in P. calyptrata, P. lanceolata and P. myrtifolia not examined
by SEM). Vessel-ray pits with distinct borders. Helical thickening
present. Vascular tracheids common. Fibres thin- to thick-walled. Axial
parenchyma in strands of 2–4 cells, scanty paratracheal to vasicentric,
in incomplete to complete 1–3-seriate sheaths near vessel groups,
sometimes aliform and confluent, and also marginal in 1–4-seriate
bands (P. lanceolata and P. myrtifolia). Rays are 1 or 2(3)-seriate (up to
4-seriate in P. rotundifolia), composed mostly of square and upright
cells (P. myrtifolia), or mostly of procumbent cells, with 1–4 marginal
rows of square and upright cells. Crystals not observed. Silica bodies in
ray cells of P. lanceolata and P. myrtifolia. Yellowish-brown deposits in
a few vessels of P. myrtifolia.
3.2.6. Stirtonanthus
Material studied: S. insignis (Compton) B.-E.van Wyk & A.L. Schutte
(BEVW 3331, 14 mm), S. taylorianus (L. Bolus) B.-E.van Wyk & A.L.
Schutte (BEVW 3169, 28 mm).
Wood diffuse-porous. Growth rings distinct, marked by flattened
latewood fibres, and also by marginal axial parenchyma (S. insignis)
or by difference in vessel diameter between late- and earlywood
(S. taylorianus). Vessels narrow, rounded to angular in outline, in dendritic pattern. Intervessel pits alternate, vestured, with scanty vestures
located at edge of inner aperture, appearing as simple rounded warts.
Vessel-ray pits with reduced borders. Helical thickenings present. Vascular tracheids common. Fibres thin- to thick-walled in S. taylorianus
and very thick-walled in S. insignis. Axial parenchyma in strands of
2(3) cells, sometimes fusiform, scanty paratracheal to vasicentric and
confluent, in incomplete to complete uniseriate (sometimes up to 3seriate) sheaths near vessel groups, and also banded, in interrupted tangential (sometimes marginal) 1–3-seriate bands (S. insignis). Rays 1–3seriate, mostly of procumbent cells, sometimes with 1–3 marginal rows
of square and upright cells (S. taylorianus), or mostly of square cells
mixed with procumbent and upright cells throughout ray (S. insignis).
Crystals not observed. Silica bodies in ray cells. Deposits in vessels not
observed.
3.2.7. Virgilia
Material studied: V. divaricata Adamson (AO 16-09, 43 mm; KK 0210, 28 mm), V. oroboides subsp. oroboides (P.J. Bergius) T.M. Salter
(BEVW 5722, 55 mm), V. oroboides subsp. ferruginea B.-E. van Wyk
(KK 44-11, 23 mm).
Wood diffuse-porous. Growth rings absent or indistinct, marked by
tangential rows of larger vessel groups (V. divaricata [AO 16-09]). Vessels narrow to relatively wide, angular to rounded in outline, solitary,
in clusters and radial multiples of 2–4(6). Intervessel pits alternate, vestured, in V. oroboides subsp. oroboides with rather numerous seemingly
unbranched vestures near inner apertures (vestures not examined by
SEM in V. divaricata and V. oroboides subsp. ferruginea). Vessel-ray pits
with distinct borders. Helical thickenings absent. Vascular tracheids
rare. Fibres thin- to thick-walled. Axial parenchyma in strands of 2–5
cells, scanty paratracheal to vasicentric, sometimes aliform, in complete
or incomplete 1–3-seriate sheaths near vessels and vessel groups. Rays
1–3-seriate. Bi- and triseriate rays of procumbent cells, sometimes with
1–2(4) marginal rows of upright and square cells. Uniseriate rays consist mostly of square and upright cells, with few procumbent cells. Acicular crystals in sheaf-like aggregates in ray and axial parenchyma cells.
A.V. Stepanova et al. / South African Journal of Botany 89 (2013) 244–256
253
Silica bodies in ray cells of V. divaricata (AO 16-09). Yellowish-brown
deposits in a few vessels.
a predominance of procumbent cells in the rays, whereas the sprouters
share rays that consist mostly of square and upright cells.
3.2.8. Amphithalea
Material studied: A. ericifolia (L.) Eckl. & Zeyh. (ALS 617, 4 mm),
A. rostrata A.L. Schutte & B.-E. van Wyk (ALS 629, 5 mm), A. vlokii
(A.L. Schutte & B.-E.van Wyk) A.L. Schutte (ALS 743, 5 mm).
Wood diffuse-porous. Growth rings absent (A. ericifolia) or distinct
to faint marked by marginal parenchyma. Vessels very narrow
(5–18 μm in tangential diameter), mostly rounded in outline, in radial
multiples and clusters of 2–10 vessels, rarely solitary, with tendency
to dendritic arrangement. Intervessel pits alternate, vestured (vestures
not examined by SEM). Helical thickenings on vessel walls common
(A. vlokii), rare (A. ericifolia) or absent (A. rostrata). Vessel-ray pits
with distinct borders. Vascular tracheids common. Fibres very thickwalled. Axial parenchyma fusiform and in strands of 2 cells (A. vlokii)
or 2–4 cells (A. rostrata), scanty paratracheal (A. vlokii) to vasicentric
(A. rostrata), and marginal, in 1 or 2-seriate tangential rows (A. vlokii)
or 2–4-seriate bands (A. rostrata). Rays 1 or 2(3)-seriate, mostly of
square cells mixed with procumbent cells throughout ray. Small prismatic crystals, solitary or aggregated small navicular crystals, and crystal sand in ray cells of A. rostrata and A. vlokii. Silica bodies common in
ray and axial parenchyma cells of A. rostrata. Brown deposits in vessels
in all studied species.
3.4. Character evolution within the Podalyrieae
3.2.9. Xiphotheca
Material studied: X. canescens (Thunb.) A.L. Schutte & B.-E.van Wyk
(ALS 595a, 9 mm), X. elliptica (DC.) A.L. Schutte & B.-E.van Wyk. (ALS
600, 8 mm), X. phylicoides A.L. Schutte & B.-E.van Wyk (ALS 648,
5 mm), X. tecta (Thunb.) A.L. Schutte & B.-E.van Wyk (ALS 597, 11 mm).
Wood diffuse-porous. Growth rings absent (X. tecta) or distinct,
marked by marginal parenchyma, flattened latewood fibres, and sometimes also by tangential band of vessels and vascular tracheids in earlywood (X. canescens). Vessels narrow, rounded to angular in outline,
mostly in clusters of 3–6 and large radial multiples (X. tecta), or in dendritic pattern (X. canescens). Intervessel pits alternate, vestured in
X. tecta with scanty vestures located at edge of inner aperture, appearing
as weakly branched coarse protuberances (vestures not examined by
SEM in X. canescens, X. elliptica and X. phylicoides). Vessel-ray pits
with reduced to distinct borders. Helical thickenings present. Vascular
tracheids common. Fibres very thick-walled. Axial parenchyma fusiform and in 2-celled strands, scanty paratracheal (X. tecta) to mostly
vasicentric (X. canescens), and also in uniseriate marginal rows
(X. canescens) or in 1–4 seriate tangential bands (X. tecta). Rays 1 or
2(3)-seriate, up to 4-seriate in X. elliptica. Multiseriate rays mostly of
square and upright cells mixed with few (X. tecta) or quite numerous
(X. canescens) procumbent cells throughout ray. Crystals not observed.
Silica bodies in ray and axial parenchyma cells. Yellowish-brown deposits in a few vessels of X. canescens and X. tecta.
3.3. Numerical analysis
The effects of fire-survival strategies on wood structure were assessed
by one-way analysis of variance (ANOVA) using the F-test for quantitative wood characters (Table 1), and the Chi-square test for two types of
rays (with a predominance of procumbent cells vs square and upright
cells). The variability of wood characters was compared amongst and
within two groups of samples representing seeders (reseeders) and
sprouters (resprouters). As these groups differ greatly in the average
size of the wood samples (mean sample radius 10.8 mm for seeders
and 5.0 mm for sprouters), the 12 largest samples of both groups (with
a radius N9 mm) were excluded from the data matrix to avoid the potential influence of sample size on the results.
A comparison of the wood anatomical data between the two groups
revealed a statistically significant effect (p b 0.0001) of fire-survival
strategy on the ray composition. All the seeder samples included show
Character states of the quantitative wood features listed in Table 1 as
well as some qualitative ones were plotted on the tree topology based
on the combined simultaneous parsimony analysis of ITS and rbcL
data for Podalyrieae (Boatwright et al., 2008). Patterns of variation for
a few wood features [the occurrence of a dendritic vessel arrangement
(Fig. 6A), helical thickenings (Fig. 6B), fibre wall thickness (Fig. 6C)
and acicular crystals in sheaf-like aggregates (Fig. 6D)], are apparently
consistent with the topology of the phylogenetic tree and support the
four main clades in Fig. 6.
4. Discussion
The wood diversity within the tribe Podalyrieae is due mainly to
variations in the grouping and arrangement of vessels, as well as in
the occurrence of helical thickenings on the vessel walls. Most members
of the genera Amphithalea, Cyclopia, Liparia, Podalyria, Stirtonanthus, and
Xiphotheca share large vessel grouping, commonly arranged in dendritic
or diagonal patterns, and the presence of helical thickenings. In Cadia,
Calpurnia and Virgilia as well as in the single species of Liparia
(L. splendens), however, smaller vessel groups (up to 7 vessels), without
a distinct arrangement, co-occur with the absence of helical thickenings.
An apparent loss of helical thickenings in combination with large vessel
grouping is found only in Amphithalea rostrata, whereas Cyclopia
maculata shows relatively small vessel grouping and very prominent
helical thickenings.
An increasing degree of vessel grouping — a transition from solitary
vessels and small isolated groups to large groups and a dendritic pattern, has been noted in genistoid tribes closely related to Podalyrieae,
i.e. in Genisteae, Thermopsideae and Crotalarieae (Metcalfe and Chalk,
1950; Yatsenko-Khmelevsky, 1954; Grosser, 1977; Baretta-Kuipers,
1981; Fahn et al., 1986; Schweingruber, 1990; Van Wyk and Schutte,
1995; InsideWood, 2004–onwards; Schweingruber et al., 2011; and
our unpublished observations) as well as in some members of the
tribes Sophoreae (Gasson, 1994), Hedysareae (Benkova and
Schweingruber, 2004); Galegeae (Fahn et al., 1986), Loteae
(Schweingruber et al., 2011) and the subfamily Caesalpinioideae
(Cozzo, 1951; Schweingruber et al., 2011). This trend can be postulated
to be an adaptation to water stress, because the vessel groups provide
the bypass water conduits in the case of an embolism of some vessels
(Zimmermann, 1983; Carlquist, 1987; Sperry, 2003). This hypothesis
on the adaptive value of vessel grouping was recently demonstrated
in experiments (Lens et al., 2011). Helical thickenings are mostly
present in shrubs growing in Mediterranean climates. High percentages
of species with spiral thickening were noted in Californian chaparral as
well as in maquis and batha biomes in Israel (Baas and Carlquist, 1985;
Carlquist, 1987). Batha is a secondary vegetation type comprising
Mediterranean semi-shrubs that colonise abandoned cultivated lands
in Israel.
The shifts in fire-survival strategy between seeders and sprouters
are considered by Schnitzler et al. (2011) to be one of the most important factors for the evolutionary diversification of the Podalyrieae. Recently, Pratt et al. (2012) found that sprouters show lower water
stress resistance but higher efficiency of xylem transport than seeders.
Within Podalyrieae, no significant differences were found in the wood
characters related to the safety and efficiency of water transport (vessel
diameter, frequency and grouping) between the species with these two
strategies. Nevertheless, we found that the rays in seeders consist of numerous procumbent cells whilst those of sprouters have mainly square
and upright cells. This difference in ray composition is unlikely to be related to the safety or efficiency of xylem transport. Rather, this character
reflects a difference in the rate of radial growth (especially during the
254
A.V. Stepanova et al. / South African Journal of Botany 89 (2013) 244–256
Fig. 6. Distribution of the wood character states reconstructed onto a subsample of the tree based on the combined simultaneous parsimony analysis of ITS and rbcL data for Podalyrieae
(modified from Boatwright et al., 2008). (A) Occurrence of dendritic vessel arrangement: white — no arrangement, black — diagonal or dendritic arrangement; (B) occurrence of helical
thickenings: white — absent, black — present; (C) fibre wall thickness: white — thin or thin to thick, black — very thick; (D) occurrence of acicular crystals in sheaf-like aggregates: white —
absent, black — present.
early stages of stem development) that seems to be faster in seeders
than in sprouters. This explanation agrees with the difference in habit
between these fire-survival strategies. Commonly, seeders form a single, tall and relatively thick stem, whereas sprouters produce numerous
thin stems from an underground lignotuber (Schutte et al., 1995).
The wood anatomy of all tree genera is very similar, and also strongly supports the inclusion of Cadia in the Podalyrieae (Boatwright et al.,
2008). It was shown that Cadia should be excluded from the Cadia
group of Sophoreae s.l. because it has very narrow rays and no crystals
(Gasson, 1994). Our study shows that most of the Podalyrieae have 1
or 2- or 1–3-seriate rays. In four genera (Liparia, Podalyria, Stirtonanthus
and Xiphotheca), crystals were not observed. The similarity in wood
anatomy is especially close between Cadia and Calpurnia, the main difference being the presence of crystals in the latter.
As molecular phylogenetic analysis (Boatwright et al., 2008) suggested, Cadia belongs to the basal-most lineage of Podalyrieae. Thereafter the Cyclopia clade diverges. Then Calpurnia and Virgilia form a
weakly supported clade that is sister to the rest of Podalyrieae. The
members of these basally diverged clades show some common wood
features. Cadia, Calpurnia and Virgilia have pits with numerous vestures,
vessel-ray pits with distinct borders as well as the absence of helical
thickenings and relatively small vessel groups. On the other hand,
Calpurnia Cyclopia and Virgilia, share the very distinctive feature of the
occurrence of acicular crystals in sheaf-like aggregates. Although the
A.V. Stepanova et al. / South African Journal of Botany 89 (2013) 244–256
patterns of variation in these wood characters (Fig. 6A, B and D) are consistent with the topology of the phylogenetic tree (including the monophyly of the Virgilia/Calpurnia clade) proposed by Boatwright et al.
(2008), the wood anatomical data do not contribute to the clarification
of relationships between the early diverged lineages of Podalyrieae
which remain poorly resolved.
As for the rest of the Podalyrieae, the members of the Liparia/
Podalyria/Stirtonanthus subclade have mostly thin- to thick-walled fibres whereas all species of its sister subclade, comprising Amphithalea
and Xiphotheca, show the presence of very thick-walled fibres. As the
character mapping suggests, modifications from very thick-walled fibres in Podalyrieae to thinner fibre walls occurred at least three times
in the course of its evolution (i.e. in the Cyclopia, Virgilia/Calpurnea,
and Liparia/Podalyria/Stirtonanthus clades).
The Podalyrieae show a remarkable diversity of crystals in the
axial and radial parenchyma. Amongst its related genistoid tribes
Thermopsideae, Genisteae and Crotalarieae, the presence of crystals
has thus far been reported only in a single species of Calobota belonging to the Crotalarieae (Metcalfe and Chalk, 1950; YatsenkoKhmelevsky, 1954; Grosser, 1977; Fahn et al., 1986; Schweingruber,
1990; Schweingruber et al., 2011; InsideWood, 2004–onwards;
Oskolski et al., in prep.). Prismatic crystals are commonly found in
Fabaceae wood (Gasson, 1994), whilst in Podalyrieae we also observed acicular crystals in sheaf-like aggregates, solitary and aggregated
navicular crystals, as well as crystal sand. Different types of crystals may
be present in the same genus as, for example, in Calpurnia. Acicular crystals in sheaf-like aggregates have been described in the bark of Virgilia
(Kotina et al., 2013-in this issue). It is also noteworthy that in Fabaceae,
crystals occur mainly in axial parenchyma cells, commonly in chambered parenchyma and less often in ray cells. In a few well-studied
tribes of Papilionoideae, prismatic crystals in ray cells were not found
in Dipterygeae, whilst they do occur in Millettieae, Sophoreae, and
Swartzieae (Fujii et al., 1994; Gasson, 1994, 2000; Gasson et al., 2004).
However, in all these tribes, species with crystals in the rays are much
less numerous than those with crystals in chambered axial parenchyma
cells. In the species of Podalyrieae, crystals are localised in ray cells but
acicular crystals in sheaf-like aggregates are also often found inside
vessels. The occurrence of acicular crystals in the intervessel pits of
Cyclopia intermedia is especially noteworthy. Such crystals are very
rare within angiosperms and have been described in detail only in the
fern genus Botrichium Sw. (Morrow and Dute, 2002).
The common occurrence of silica bodies in the ray and axial parenchyma cells in most species of Podalyrieae (this trait is absent or lost
only in particular species of Amphithalea, Calpurnia, Podalyria and
Virgilia) is rather surprising. Silica bodies occur in several genera of
Caesalpinioideae, namely Apuleia Gaertn., Dialium L., Dicorynia Benth.,
Distemonanthus Benth., Loesenera Harms., Sclerolobium Vogel and
Tachigali Aubl. but are not found in any Mimosoideae (InsideWood,
2004). They are also absent in all but one species of Papilionoideae investigated (Gasson, 1994; Fujii et al., 1994; Gasson et al., 2004; et al.).
The occurrence of silica bodies in ray cells was reported in Calobota
saharae (Coss. and Dur.) Boatwr. & B.-E.van Wyk (InsideWood, 2004,
as Genista saharae Coss. & Dur.). This species belongs to the tribe
Crotalarieae that is closely related to the Podalyrieae. Thus the occurrence of silica bodies seems to be a shared character state of these two
tribes. However, further wood anatomical studies of other genistoid
groups are necessary to clarify the distribution and evolutionary trends
for this character.
5. Conclusions
Our wood anatomical study of several members of all genera belonging to the tribe Podalyrieae has led to the following new insights:
(1) wood anatomical characters allow for the distinction between
some genera, especially if unique combinations of characters are taken
into account; (2) variation in some wood characters (vessel grouping
255
and arrangement, and occurrence of helical thickenings) is consistent
with the idea that their evolution occurred independently in different
lineages of Podalyrieae in the course of adaptation to seasonally arid
environments; (3) unlike the related genistoid tribes, the Podalyrieae
show a remarkable diversity of crystals in the axial and radial parenchyma; (4) the placement of Cadia in the Podalyrieae is confirmed by
wood anatomical data; (5) the occurrence of sheaf-like crystals and
the thickness of fibres are apomorphic features for some subclades of
Podalyrieae; and (6) within the Podalyrieae, seeders can be distinguished from sprouters by some ray features related to their habits,
but they show no differences in the wood characters related to the safety and efficiency of water transport. Therefore, the observed range of
wood diversity related both to habit and habitat, and to the phylogenetic relations within Podalyrieae, provides us with a better understanding
of the trends and conditions of plant diversification that have occurred
in the Cape region.
Acknowledgements
The authors thank the National Research Foundation (South Africa),
the University of Johannesburg (UJ) and the Russian Foundation of Basic
Research (grant # 12-04-01684) for funding. We also thank the personnel of the SEM unit at UJ for their help.
References
Baas, P., Carlquist, S., 1985. A comparision of the ecological wood anatomy of the floras of
Southern California and Israel. IAWA Bulletin 6, 349–353 (n.s.).
Baretta-Kuipers, T., 1981. Wood anatomy of Leguminosae: its relevance to taxonomy. In:
Polhill, R.M., Raven, P.H. (Eds.), Advances in Legume Systematics 1. Royal Botanical
Gardens, Kew, pp. 677–705.
Beaumont, A.J., Beckett, R.P., Edwards, T.J., Stirton, C.H., 1999. Revision of the genus
Calpurnia (Sophoreae: Leguminosae). Bothalia 29, 5–23.
Benkova, V.R., Schweingruber, F.H., 2004. Anatomy of Russian woods. An atlas for the
identification of trees, shrubs, dwarf shrubs and woody lianas from Russia. Swiss Federal Institutes for Forest, Snow and Landscape Research.Bern, Stuttgart, Birmensdorf.
Boatwright, J.S., Savolainen, V., Van Wyk, B.-E., Schutte-Vlok, A.L., Forest, F., Van der Bank,
M., 2008. Systematic placement of the anomalous genus Cadia and the phylogeny of
the tribe Podalyrieae. Systematic Botany 33, 133–147.
Carlquist, S., 1982. The use of ethylenediamine in softening hard plant structures for paraffin sectioning. Stain Technology 57, 311–317.
Carlquist, S., 1987. Diagonal and tangential vessel aggregations in wood: function and relationship to vasicentric tracheids. Aliso 11, 451–462.
Cozzo, D., 1951. Anatomia del leno secundario de las Leguminosas Mimosoideas y
Caesalpinoides Argentinas silvestres y cultivadas. Revista del Museo Argentino de
cienicas Naturales “Bernardino Rivadavia” e Instituto Nacional de Investigacion de
las Ciencias Naturales (Argentina). Botanica 2, 63–146.
Fahn, A., Werker, E., Baas, P., 1986. Wood anatomy and identification of trees and shrubs
from Israel and adjacent regions. Israel Academy of Sciences and Humanities, Jerusalem.
Fujii, T., Baas, P., Gasson, P., Ridder Numan, J.W.A., 1994. Wood anatomy of the Sophora
group (Leguminosae). In: Ferguson, I.K., Tucker, S. (Eds.), Advances in Legume Systematics 6. Royal Botanic Gardens, Kew, pp. 205–249.
Gasson, P., 1994. Wood anatomy of the tribe Sophoreae and related Caesalpinioideae and
Papilionoideae. In: Ferguston, I.K., Tucker, S. (Eds.), Advances in Legume systematics
6. Royal Botanical Gardens, Kew, pp. 165–203.
Gasson, P., 2000. Does wood anatomy support tribal and generic classification in
papilionoid Leguminosae? In: Herendeen, P.S., Bruneau, A. (Eds.), Advances in Legumes Systematics 9. Royal Botanical Gardens, Kew, pp. 201–215.
Gasson, P., Wray, E., Schrire, B.D., 2004. Wood anatomy of the tribe Millettieae with comments on related papilionoid Leguminosae. IAWA Journal 25 (4), 485–545.
Grosser, D., 1977. Die Hölzer Mitteleuropas. Ein mikrophotographischer Lehratlas,
Springer, Berlin.
IAWA Committee, 1989. IAWA list of microscopic features for hardwood identification.
IAWA Bulletin 10, 221–331.
InsideWood, 2004. Onwards, Published on the Internet http://insidewood.lib.ncsu.edu/
search (date of accession: 29.03.2013).
Jansen, S., Kitin, P., Pauw, H. De, Idris, M., Beeckman, H., Smets, E., 1998. Preparation of
wood samples for transmission light microscopy and scanning electron microscopy.
Belgian Journal of Botany 131, 41–49.
Jansen, S., Choat, B., Vinckier, S., Lens, F., Schols, P., Smets, E., 2004. Intervascular pit membranes with a torus in the wood of Ulmus (Ulmaceae) and related genera. New
Phytologist 163, 51–59.
Johansen, D.A., 1940. Plant Microtechnique. McGraw-Hill, New York.
Kotina, E.L., Oskolski, A.A., Stepanova, A.V., Van Wyk, B.-E., 2013. Notes on the taxonomic
and ecological significance of bark structure in the genus Virgilia (Fabaceae,
Podalyrieae). South African Journal of Botany 89, 240–243 (in this issue).
Kukachka, B.F., 1977. Sectioning Refractory Woods for Anatomical Studies. USDA Forest
Research Note FPL-0236. USDA Forest Service Forest Products Laboratory, Madison,
Wisconsin.
256
A.V. Stepanova et al. / South African Journal of Botany 89 (2013) 244–256
Lens, F., Sperry, J.S., Christman, M.A., Choat, B., Rabaey, D., Jansen, S., 2011. Testing hypotheses that link wood anatomy to cavitation resistance and hydraulic conductivity in
the genus Acer. New Phytologist 190, 709–723.
MacLachlan, I., Gasson, P., 2010. Quantitative wood anatomy using multivariate principal components analysis for identification of the CITES listed Pterocarpus
santalinus (Dalbergioideae, Papilionoideae, Leguminosae). IAWA Journal 31,
121–138.
Maddison, W.P., Maddison, D.R., 2007. Mesquite: a modular system for evolutionary
analysis. Version 2.00. Published on the Internet http://mesquiteproject.org (date of
accession: 29.03.2013).
Metcalfe, C.R., Chalk, L., 1950. Anatomy of the dicotyledons, 1. Oxford University Press,
Oxford.
Morrow, A.C., Dute, R.R., 2002. Crystals associated with the intertracheid pit membrane of
the woody fern Botrychium multifidum. American Fern Journal 92, 10–19.
Pratt, R.B., Jacobsen, A.L., Jacobs, S.M., Esler, K.J., 2012. Xylem transport safety and efficiency differ among fynbos shrub life history types and between two sites differing in
mean rainfall. International Journal of Plant Sciences 173, 474–483.
Schnitzler, J., Barraclough, T.G., Boatwright, J.S., Goldblatt, P., Manning, J.C., Powell, M.P.,
Rebelo, T., Savolainen, V., 2011. Causes of plant diversification in the Cape biodiversity
hotspot of South Africa. Systematic Biology 60, 343–357.
Schutte, A.L., Van Wyk, B.-E., 1998. Evolutionary relationships in the Podalyrieae and
Liparieae (Fabaceae) based on morphological, cytological, and chemical evidence.
Plant Systematics and Evolution 209, 1–31.
Schutte, A.L., Vlok, J.H.J., Van Wyk, B.-E., 1995. Fire-survival strategy — a character of taxonomic, ecological and evolutionary importance in fynbos legumes. Plant Systematics
and Evolution 195, 243–259.
Schutte-Vlok, A.L., Van Wyk, B.-E., 2011. A taxonomic revision of Podalyria (Fabaceae).
Systematic Botany 36, 631–660.
Schweingruber, F.H., 1990. Anatomy of European Woods. Verlag Paul Haupt, Bern and
Stuttgart.
Schweingruber, F.H., Börner, A., Schulze, E.-D., 2011. Atlas of stem anatomy in herbs,
shrubs and trees, vol. 1. Springer, Heidelberg.
Sperry, J.S., 2003. Evolution of water transport and xylem structure. International Journal
of Plant Sciences 164, S115–S127.
Van der Bank, M., Chase, M.W., Van Wyk, B.-E., Fay, M.F., Van der Bank, F.H., Reeves, G.,
Hulme, A., 2002. Systematics of the tribe Podalyrieae (Fabaceae) based on DNA,
morphological and chemical data. Botanical Journal of the Linnean Society 139,
159–170.
Van Wyk, B.-E., 2005. Tribe Podalyrieae. In: Lewis, L., Schrire, B., Mackinder, B., Lock, M.
(Eds.), Legumes of the World. Royal Botanic Gardens, Kew, pp. 267–271.
Van Wyk, B.-E., Schutte, A.L., 1995. Phylogenetic relationships in the tribes Podalyrieae,
Liparieae and Crotalarieae. In: Crisp, M., Doyle, J.J. (Eds.), Advances in Legume Systematics 7: Phylogeny. Royal Botanic Gardens, Kew, pp. 283–308.
Yatsenko-Khmelevsky, A.A., 1954. Caucasian woods, 1. Academy of Sciences of the
Armenian Soviet Socialist Republic, Yerevan (in Russian).
Zimmermann, M.H., 1983. Xylem Structure and the Ascent of Sap. Springer, Berlin.
Anna Stepanova