zyxwvutsrqp zyxwvutsrqpo zyxwvu zyxwv zyx Botanical journal of the Linnean Socieo (1988), 97: 63-71. With 4 figures The endotheciurn in Senecio (Asteraceae) P. LESZEK D. VINCENT, F.L.S Department of Plant Sciences, Rhodes University, P . O . Box 94, Grahamstown, 6140, Republic of South Africa AND FIONA M. GETLIFFE, F.L.S. Department of Botany, University of Natal, P. 0 . Box 375, Pietermaritzburg, 3200, Republic of South Africa zyxwvutsr Received July 1987, accepted for publication September 1987 VINCENT, P. L. D. & GETLIFFE, F. M., 1988. The endothecium in Senccio (Asteraceae). The configuration of the endothecium was examined in a large number of senecios, predominantly from Natal, South Africa, together with a few representatives of other genera in the Senecioneae. The term ‘inner anticlinal’ is recommended as being more accurate than ‘radial’ for the description of the configuration of the endothecium in Senecio. All but two of the taxa studied had the inner anticlincal configuration of the endothecium. ADDITIONAL KEY WORDS:-Compositae - Endothecium configuration. CONTENTS Introduction . . . Material and methods . Observations . . . Discussion. . . . Conclusion . . . References. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 63 66 66 69 71 71 INTRODUCTION Attention has been drawn to the value of the endothecium in taxonomy by Dormer (1962) and Noel (1983), and by Nordenstam (1978) with reference to the Asteraceae, by Arora & Tiagi (1977) in the Apiaceae and by Eyde (1977) in the Onagraceae. Noel (1983) mentions that “there are indications of constancy at the generic level, or even through larger groups such as the Asteraceae”. The endothecium or fibrous layer is the subepidermal cellular layer of the anther wall in angiosperms (Esau, 1977). The fibrous layer forming the cell + 0024-4074/88/050063 09 $03.00/0 zyxwvut 63 0 1988 The Linnean Society of London zyxwvutsr zyxwvut zyxwv zyxw zyxwvutsrqponmlkjih zyxwvutsrqponmlk TABLE 1 . Species and varieties of Senecio and related genera included in this study (110 taxa) zyxwvutsrqponml zyxwvutsrqponm zyx S. achilleifolius DC. S. afinis DC. S. albanenris DC. var. doronicijoms (DC.) Harvey S. unomalochrous Hilliard S. urubidifolius 0.Hoffmann S. nrperulus DC. S. burbutus DC. S. barbertonicus Klatt S. brachypodus DC. S. brevidentatus M.D. Henderson S. brevilom Hilliard S. bupleuroides DC. S. cathcartenris 0. Hoffmann S. cuudatus DC. S. chrysocoma Meerburgh S. cissampelinus (DC.) Schultz Bip. ( = Mikaniopsis cissampclina (DC.) C. Jeffrey,fide Jeffrey, 1986) S. consanguineus DC. S. coronatus (Thunberg) Harvey S. dcltoideus Lessing S. discodregeunus Hilliard & Burtt S. dregeanus DC. S. erubescens Aiton var. erubescens var. crepid$olius DC. var. incisus DC. var. dichotomus DC. S. fulgens (Hook. fil.) Nicholson (=Kleiniu fulgens Hook. fil.fide Jeffrey, 1986) S. gerrurdii Harvey S. glubem'mus DC. S. glunduloso-lanosus Thellung NATAL SENECIOS S. glanduloso-pilosus Volkens & Muschler S. humcianus MacOwan s. hastnfus L. S. huygarthii Hilliard S. heliopsis Hilliard & Burtt S. helminfhioides (Schultz Bip.) Hilliard S.hieracioides DC. S. hirsutilobuc Hilliard S.Iypochoeridcur DC. S. inaequidens DC. S. ingeliensis Hilliard S. inornafus DC. S. juniperinus L.f. S. latifolius DC. S. &denburg& Hutchinson & Burtt Davy S. macrocephulus DC. S. manospermus DC. S. madagascariensis Poiret S. mauricei Hilliard & Burtt S. medley-woodii Hutchinson S. microglossus DC. S. mikanioides Otto ex Harvey ( =Delairea odorata Lem. Jide Jeffrey, 1986) S. mooreanus Hutchinson S. nafuluola Hilliard S. ngyanus Hilliard S. othonnijoms DC. S. ox~~iifolius DC. S. puludafinis Hilliard S. panduriiormis Hilliard S. pbisfocephulus Spencer Moore S.polyanthemoides Schultz Bip. S. polyodon DC. var. pohodon var. subgluber (0.Kuntze) Hilliard & Burtt S. poseidconis Hilliard & Burtt radiate form discoid form S.sp. aff. S. posdeonis S.praetm'tus Kllick S.pterophorus DC. s.purpureus L. S. radkuns (L.f.) Schultz Bip. S. refrorsus DC. S. rhomboideus Harvey S. rhyncholamus DC. S. sandersonii Harvey S.sanienris HiIJiard & Burtt S. scitlcr Hutchinson & Burtt Davy S. seminiveus Wood & Evans S. smatuloides DC. S. skirrhodon DC. S.speciosus Willdenow S.sp. aK S. speciosus S. subcoriaceus Schlechter S. subrubnJloms 0. Hoffmann S. tumoides DC. S. tanacetopsis Hilliard s. transvanlensis Bolus (= Emilia trunruaalensis (Bolus) C. Jeffrey, j d c Jeffrey, 1986) S. umgeniensis Thellung S. urophyllus Conrath S. variabilis Schultz Bip. S. viminalis Bremekamp zyxwv zyxwvutsrqponmlk zyxwvutsrqpon zyxwvutsrq zy CAPE HETEROCHROMOUS NON-YELLOW (PURPLE) SENECIOS S.arenarius Thunb. S. cakilefolius DC. S. multibracteatus Ham. S. elegans L. S. grand$orus Berg. NON-SOUTHERN AFRICAN SENECIOS S.califmicus DC. S. hockii De Wild. & Muschl. S. desjontainei Druce S. erechtitoides Bak. S . gallicus Chaix (=Emilia hockii (De Wild. & Muschl.) C. Jeffrey,jde Jeffrey, 1986). S. lautus Willd. S. syluaticus L. S. syrzngtJolius 0. Hoffm. S. vernalis Waldst. & Kit. S. uiscosus L. S . vulgaris L. 4 OTHER GENERA IN THE TRIBE SENECIONEAE Cineraria geiyolia L. Crassocephalum cemuum (LX) Moench nom. illeg. ( = C . rubens (Jacq.) S . Moore) Emilia flammea Cass. nom. illeg. ( = E . jauanica (Burm. fil.) Merr.) Gynura diuaricata (L.) DC. Notonia grandgora DC. ( = Kleinia grandgora (DC.) N. Rani,@ Jeffrey, 1986: 935) Kleinia nerizfilia Haw. 5im 3 sE G 5 i 2 3 2 zzzy 66 zyxwvutsr zyxwvutsrqp P. L. D. VINCENT AND F. M. GETLIFFE walls often differentiates on the anticlinal, periclinal and transverse walls of the cells forming distinct ribs or bars (Esau, 1977). Dormer (1962), in his study of the ‘fibrous layer’ or endothecium of some members of the Asteraceae, described the anticlinal walls (or sides) of an endothecial cell as possessing “in most cases prominent internal ribs of thickening”. These ribs are perpendicular to the anther surface and span the full depth of the cell between the periclinal walls. Usually one or more ribs continued round the corners and on to the periclinal walls, but the periclinal walls of some species lacked these ribs of localized thickening. Dormer (1962), Nordenstam (1976, 1978) and Wetter (1983) described three configurations of these ribs, according to differences in their alignment with respect to the vertical or long axis of the pollen sac or anther. When the ribs are restricted to the transverse or horizontal walls the configuration of the endothecial tissue is said by these authors to be ‘polarized’, and when the cells are ribbed all around, the configuration is said to be ‘radial’. Robinson & Brettell (1973) restricted the definition of the ‘radial’ configuration to include only those cells with ribs on the ‘vertical’ (‘radial’) walls. When the endothecial cells are more or less uniformly thickened and without distinct ribs, the configuration of the endothecial tissue is called ‘transitional’ (Dormer, 1962; Nordenstam, 1978; Wetter, 1983). In many members of the Asteraceae, except in the tribe Lactuceae (Nordenstam, 1978), the ‘transitional’ form of configuration of the endothecial tissue is restricted to a narrow zone near the connective. zy MATERIAL AND METHODS A large number of senecios, predominantly from Natal and a few representatives of other genera in the Senecioneae, were included in the study (Table 1). A minimum of three representatives of each taxon was studied in detail. In the selection of the representatives an attempt was made to include specimens from widely different localities or habitats, to enable the effect of any environmentally induced variation to be encountered. Anthers that were partially exserted from the disc corolla were sampled, to avoid studying immature endothecial tissue. De Vaal (1978) mentions that the wall thickenings attain their final form only late in the development of the anther. At least six to eight sets of syngenesious anthers from each representative were placed in Pyrex glass beakers and covered with lactic acid (c. 85%), and heated on an electric hotplate at c. 120°C until the tissue was cleared. The cleared anthers were then dissected and mounted in lactic acid (c. 85%). The determination of the type of configuration was made from cells of the abaxial surface of the anther, three or four cells away from the connective and midway between the ends of the anther. zyx OBSERVATIONS In all but two of the species studied, the structure of the endothecium is placed in one category. The endothecial cells are tabular, rectangular in periclinal view, and the thickenings are principally restricted, in each cell, to the longitudinal wall zyxwvu zyxwv THE ENDOTHECIUM IN SENECIO 67 zyxw zyxwvu zyxwvu Figure I . Inner anticlinal configuration of endothecium; view of adaxial surface of anther; longitudinal axis of anther vertical; connective down right hand side. Sample from Senecio speciosus Willdenow (Hilliurd 1061 N U ) . Scale bar= 10 pm. zyxwvuts nearest the connective, here referred to as the inner anticlinal (radial) wall. Frequently the transverse (horizontal) walls are also thickened. In periclinal view these ribs appear as thickenings down the edge of the inner anticlinal wall (Fig. 1). When viewed in a periclinal-anticlinal orientation the ribs appear slightly convex and span the width of the cell between the periclinal walls (Figs 2 & 3). Some of these ribs possessed a median transverse bar (Fig. 3 ) . This inner anticlinal pattern of thickening was found on the abaxial (outer) surfaces of the endothecium of the anther, excluding the first two or three cells nearest the connective. Beyond the almost imperceptible region where adjacent anthers fuse, the adaxial (inner) surfaces of the anther, the endothecial pattern is of the ‘polarized’ form, sensu Dormer ( 1962). Dormer (1962) noted a distinct sequence in the progression of the endothecial patterns within an anther. This is as follows: starting from either edge of the connective and moving round the anther to the adaxial surface, the patterns, 68 P. L. D. VINCENT AND F. M. GETLIFFE zyxwvutsrq zyxwvu zyx zy zyx zy Figure 2. Three isolated cells with the inner anticlinal configuration; view of adaxial surface; longitudinal axis of anther vertical; periclinal-anticlinal orientation; connective opposite right hand side of cells. Sample from Senecio sandersonit’ Harvey (Hilliard B Burtt 5887 NU). Scale bar = 10 pm. insofar as they are present at all, occur consistently in the order ‘transitional’, ‘radial’, ‘polarized’. In our study the ‘transitional’ pattern of configuration was seldom found, while the order of occurrence of ‘radial’ and ‘polarized’ patterns is the same as that described by Dormer (1962). The two exceptions to the patterns described so far occur in specimens of Senecio cissampelinus (DC.) Sch. Bip. and Gynura diuaricata (L.) DC. In S. cissumpelinus, the endothecial pattern is predominantly ‘polarized’, but irregularly placed ribs are also found along both anticlinal walls, spanning the width between the two periclinal walls. In G. auriculata, each cell has a distinct imperforate base plate with a number of rib-like extensions from both anticlinal edges of the base plate (Fig. 4). This base plate is adjacent to the abaxial surface of the anther. In some instances these rib-like extensions continue round the corner of each anticlinal wall and span the width of the anticlinal wall. This configuration is similar to that described by Noel (1983) in Valerianu capensis Thunb. It should be noted that since the completion of this study Senecio cissumpelinus has been re-classified as Mikaniopsis cissampelina (DC.) C. Jeffrey (Jeffrey, 1986). zy zyxwvu THE ENDOTHECIUM IN SENECZO 69 zyxwvutsrq zyxwvutsrq Figure 3. Diagram of single endothecial cell illustrating convex ribs spanning the width of the inner anticlinal wall of the cell. Some ribs have a median transverse bar (arrows). Drawing from Senecio spaciosus Willdenow (Hilliard 1061 N U ) . Scale bar= 10 pm. DISCUSSION zyxw Dormer (1962), Nordenstam (1978) and Wetter (1983) describe the endothecial pattern in Senecio as ‘radial’, i.e. cells which are ribbed all round (Dormer, 1962). However, the endothecial pattern observed during this study is quite distinct in having ribs restricted to the inner anticlinal walls, and not all round the cells or ‘radial’ as described by Dormer (1962). Furthermore the illustrations provided by Wetter (1983: Figs 30 & 31) of ‘radial’ endothecia show a pattern which is identical to that reported here. We suggest that the form of endothecial pattern described during this study could best be described as ‘inner anticlinal thickening’. It is interesting to note that while Dormer (1962) described ‘radial’ thickening as comprising cells ribbed all round, Fig. 1 in Dormer’s article illustrated the pattern that we observed and regard as being distinct from the ‘radial’ pattern. Dormer (1962) reported the occurrence of ‘radial’ endothecial thickening in a number of representatives of other tribes in the Asteraceae (Astereae, Eupatorieae and Anthemideae). Whether these too, could be referred to the configuration ‘inner anticlinal’ must be determined before the significance of endothecial characters in the Asteraceae can be fully appreciated. Wetter (1983) found considerable intraspecific variation in the extent and placement of the ribs (moniliform thickenings) in the endothecial cells of some cacalioid and senecioid genera. However, in the present study, intraspecific 70 zyxwvutsrqp zyxwvutsr P. L. D. VINCENT AND F. M. GETLIFFE zyxwvuts zyxwvutsr zyxwvu Figure 4. Endothecial cells of Cynura dzuaricata (L.) DC.; view of adaxial surface of anther; longitudinal axis of anther vertical; connective down right hand side. Note the rib-like extensions from both anticlinal walls. Sample from Hu, S.H. 11678 K. Scale bar= 10 pm. variation of the endothecial pattern was not a distinct feature, the pattern being strikingly almost invariable. Dormer (1962), suggested that further investigation of the endothecium of the Asteraceae may lead to the recognition of the taxonomic significance of some of the finer details of the appearance of the endothecium. This is perhaps especially true in the Senecioneae where at least three types of endothecial configuration have been reported (Dormer, 1962). In recent evaluations of the generic concept of Senecio, Vincent ( 1984) regarded the configuration of the endothecial thickening to be one of six taxonomically important characters. Species with widely divergent endothecial patterns were recommended for exclusion from the genus, and further studies of the genus and its relatives are underway to ascertain whether the inner anticlinal configuration is constant within the genus in its narrowest sense. zy zyxwvu zyxwv T H E ENDOTHECIUM IN SENECIO 71 CONCLUSION The occurrence of more than one form of endothecial pattern in the tribe Senecioneae is anomalous and suggests that the predictions of Dormer and others of the value of endothecial patterns, may be correct. In the Senecioneae, the inner anticlinal configuration appears to be a notable characteristic of the genus Senecio, although not peculiar to the genus. A similar approach to the study of other tribes may reveal similar anomalies, with similar taxonomic implications. The full significance of these features cannot, however, be assessed until a complete survey has been carried out. Nevertheless these preliminary results support the statement by Noel ( 1983), that “there is constancy at the genus level or even through larger groups such as the Asteraceae” in the pattern of endothecial thickening. Our contention that endothecial pattern is one of six generic characters in Senecio is being tested by further studies. zy zyxwvutsrqp zyxwvu REFERENCES ARORA, K. & TIAGI, B., 1977. The role of the endothecium in the identification of Umbellifers Current Science, 46: 53 I . DE VAAL, J., 1978. Studies in the cell wall development in the endothecium of Bulbine fructescens (L.) Willd. Unpublished MSc. thesis, University of Natal, Pietermaritzburg. DORMER, K. J., 1962. The fibrous layer in the anthers of Compositae. New Phytologist, 61: 150-153. ESAU, K., 1977. Anatomy of Seed Plants. New York: John Wiley & Sons. EYDE, R. H., 1977. Reproductive structures and evolution in Ludwigia (Onagraceae). 1. Androecium, placentation, merism. Annals of the Missouri Botanical Garden, 64: 644-655. JEFFREY, C., 1986. The Senecioneae in East Tropical Africa. Notes on Compositae: IV. Kew Bulletin, 41(4): 873-943. NOEL, A. R. A,, 1983. The endothecium-a neglected criterion in taxonomy and phylogeny?. Bothalia, 14: 833-838. NORDENSTAM, B., 1976. Re-classification of Chrysanthemum L. in South Africa. Botaniska Notiser, 129: 137-165. NORDENSTAM, B., 1978. Taxonomic studies in the tribe Senecioneae (Compositae). Opera Botanica, 44: 1-84. ROBINSON, H. & BRETTELL, R. D., 1973. Studies in the Senecioneae (Asteraceae). IV. The genera Mtsadenia, Syneilesis, Miracacalia, Koyamacalia and Sinacalia. Phytologia, 27: 265-276. VINCENT, L. P. D., 1984. A study of the interrelationships of some Natal species of Senecio (Asteraceae/Compositae).Unpublished Ph.D. thesis, University of Natal, Pietermaritzburg. WETTER, M. A., 1983. Micromorphological characters and generic delimitation of some new world Senecioneae (Asteraceae). Brittonia, 35: 1-22.