Acta Botanica Brasilica - 34(1): 94-106. January-March 2020.
doi: 10.1590/0102-33062019abb0234
Morphological characterization of pollen grains of Brazilian species of
Bombacoideae (Malvaceae s.l.)
Marileide Dias Saba1* , Gerleni Lopes Esteves2 , Valdira de Jesus Santos1
and Francisco de Assis Ribeiro dos Santos3
Received: July 4, 2019
Accepted: September 18, 2019
.
ABSTRACT
The pollen grains of 15 species belonging to five genera (Ceiba Mill., Eriotheca Schott & Endl., Pachira Aubl., Pseudobombax
Dugand, and Rhodognaphalopsis A. Robyns) of the subfamily Bombacoideae (Malvaceae s.l.) were acetolysed, measured,
described and photomicrographed under light microscopy and scanning and transmission electron microscopy, in order
to characterize the pollen morphology of species of the subfamily occurring in Brazil. The pollen characters studied
were size, shape, exine constitution, and apertural type. Pollen grains were medium to large-sized and isopolar with
a (sub)circular and (sub)triangular amb with flat, convex or concave sides; oblate to suboblate; 3(-4)-colp(or)ate or
4-5(-6)-colporate, planaperturate, sinuaperturate; equatorial calottes different or not; exine tectate or semitectate,
perforate and microreticulate with or without supratectal spines. The results confirm the eurypalynous nature of
the group with variation among the studied genera being mainly in the exine pattern.
Keywords: Ceiba, Pachira, palynology, Pseudobombax, SEM, TEM
Introduction
Bombacoideae is one of nine recognized subfamilies
of Malvaceae s.l. (Bayer et al. 1999). It comprises genera
traditionally placed in the family Bombacaceae and, with
the subfamily Malvoideae, forms a clade called Malvatheca
(Alverson et al. 1999). Malvatheca is well-supported by
mixed analyses, and includes representatives characterized
by modified anthers with two or multiple sporangiate thecae.
However, the compositions of Bombacoideae and Malvoideae
are not easily determined by morphology, while molecular
studies have presented conflicting results (Baum et al. 2004;
Nyffeler et al. 2005). Traditional works (Kunth 1821; Candolle
1824; Cronquist 1981) have always considered the taxa included
in Malvoideae and Bombacoideae as being very closely related.
Bombacoideae includes about 17 genera and 160 species
with a predominantly Neotropical distribution (CarvalhoSobrinho et al. 2016). According to Stevens (2005), the
subfamily is characterized by an often robust trunk with water
storage in the parenchyma, fine bark, robust aculeus, usually
fasciculate fillets, pollen grains with a triangular amb with
more or less flat sides, staminode generally absent, pubescent
endocarp and palmately compound leaves, the latter being
considered a probable synapomorphy for the group (Alverson
et al. 1999; Baum et al. 2004).
Several representatives of Bombacoideae have numerous
uses and are of great economic importance. The light wood
of species of Cavanillesia, Ceiba, Eriotheca and Pseudobombax
is used in the manufacture of packaging, furniture structure,
door, linings, toys, and model aircrafts. The kapok is used
for filling mattresses, pillows, and furniture upholstery.
1 Departamento de Educação, Universidade do Estado da Bahia, 48970-000, Senhor do Bonfim, BA, Brazil
2 Instituto de Botânica, 01061-970, São Paulo, SP, Brazil
3 Departamento de Ciências Biológicas, Universidade Estadual de Feira de Santana, 44036-900, Feira de Santana, BA, Brazil
* Corresponding author: marileide.saba@gmail.com
Morphological characterization of pollen grains of Brazilian species of Bombacoideae (Malvaceae s.l.)
Among other species, representatives of Bombax, Ceiba,
and Pachira stand out as ornamental plants used in parks
and gardens (Braga 1960; Lorenzi 2002a; b; Maia 2004).
Bombacoideae is considered a eurypalynous subfamily
whose pollen grains vary mainly in apertural type and pattern
of exine ornamentation. The use of pollen morphology for
taxonomic differentiation is of particular importance for
eurypalynous groups. Fuchs (1967) emphasized the value of
pollen characters for differentiating taxa of Bombacoideae.
This is evidenced in the taxonomic study of Bombax s.l.
(Robyns 1963), which used pollen morphology along with
macromorphological characters to delimit infrageneric taxa,
and the classification of Cronquist (1981), which used pollen
type as one of the characters to separate representatives
included in Malvoideae and Bombacoideae.
One of the most significant contributions to the pollen
morphology of representatives of Bombacoideae is that of
Nilson & Robyns (1986), who analyzed pollen grains of 29
genera of the subfamily using light and electron microscopy.
These authors recognized eleven pollen types based mainly
on exine ornamentation patterns and apertural types.
Other important works on the pollen morphology of
species of the subfamily include Erdtman (1952), who
analyzed 90 species of 20 genera, including species of the
Brazilian flora. Robyns (1963), as previously mentioned,
used pollen characters in the taxonomic study of the
genus Bombax, including species of Eriotheca, Pachira,
Pseudobombax, Bombacopsis and Rhodognaphalopsis. Using
scanning electron microscopy, Robyns (1971) recognized
pollen types that differed with regard to apertures, amb
and sexine stratification. Tsukada (1964) highlighted
the importance of representatives of Bombacoideae in
stratigraphic studies when analyzing the pollen morphology
of fossil and extant species. Sowunmi (1973), Lozano-García
& Hernández (1990) and Palacios-Chávez et al. (1991)
included morphological descriptions of the pollen of species
of Bombacoideae in their works. Moncada & Sotolongo
(1994) described four pollen types for the genera that occur
in Cuba.
Brazilian works of significance include that of SalgadoLabouriau (1973), who recognized four pollen types for
Cerrado species; Melhem & Bissa (1985), who analyzed
the pollen morphology of Pseudobombax grandiflorum; Bove
(1993) who described the pollen grains of Pseudobombax,
Bombacopsis, Pachira and Spirotheca, which occur in the state
of Santa Catarina, grouping them into two pollen types and
three pollen subtypes; Carreira et al. (1995), who analyzed
the pollen grains of species of Bombacoideae growing in the
park of the Goeldi Museum and presented a pollen key based
on apertural type and exine ornamentation; and Abreu et al.
(2014), who analyzed eleven species, separating them by a
pollen key that considers the presence or absence of callote.
It should be noted that most descriptions were made using
light microscopy (LM), with scanning electron microscopy
(SEM) being used only in the last three cited works.
The present work aimed to describe the pollen
morphology of Brazilian species of Bombacoideae with
the aim of expanding palynological knowledge of species
of this subfamily.
Materials and methods
Pollen grains of 15 species belonging to five genera
representative of Brazilian Bombacoideae were examined
using light and electron microscopy. Anthers were removed
from specimens deposited in the herbaria ALCB, EAC,
HST, HUEFS, IPA, PEUFR, SP, SPF and TEPB, all acronyms
according to Thiers (2017, continuously updated) (Tab. 1).
For light microscopy (LM), pollen material was
acetolyzed (Erdtman 1960), mounted on slides with
glycerinated gelatin, sealed with paraffin and analyzed and
photomicrographed using a Zeiss Axiostar microscope. The
slides were deposited in the pollen collection of Laboratório
de Micromorfologia Vegetal (LAMIV) of Universidade
Estadual de Feira de Santana. Measurements of the main
morphometric parameters (equatorial and polar diameters)
were made on 25 pollen grains, whenever possible. Other
parameters (diameter of apertures and thickness of exine,
sexine and nexine) were measured for 10 randomly-chosen
pollen grains. All exine measurements were taken in the
mesocolpium region. Quantitative data were submitted
statistical analyses adequate for the sample size. The
arithmetic mean (x̄), standard deviation of the mean (Sx̄ ),
95 % confidence interval (CI) and coefficient of variation
(CV) were calculated for all of the diameter measurements
with a sample size of 25, while only the arithmetic mean was
calculated for parameters with a sample size less than 25.
Principal component analysis (PCA) using PC-ORD 5.0
software (McCune & Mefford 2011) was used to identify
the palynological variables that best contribute to the
distinction of the studied species. This analysis used ten
metric variables: polar diameter in equatorial view (P),
equatorial diameter in polar view (E), equatorial diameter
in equatorial view (Epv), shape (P/E), polar area index
(AI), ectoaperture length (EcL), ectoaperture width (EcW),
endoaperture height (Eh) and thickness of exine (Ex), nexine
(Nex) and sexine (Sex). The results were observed in a biplot
graph built from the two first principal components (PC1
and PC2) derived from the PCA.
For scanning electron microscopy (SEM), acetolyzed
pollen grains were washed in distilled water, dehydrated
in an ascending hydroethanolic series (50, 70, 80, 90 and
100 %), mounted on a SEM specimen holder, metallized
with gold, and electron micrographed using a LEO 1430
VP Electron Microscope of the Departamento de Ciências
Biológicas of the Universidade Estadual de Feira de
Santana.
Ceiba erianthos (Cav.) K. Schum. was selected, because of
the availability of material, for analysis using transmission
electron microscopy (TEM). Closed anthers were fixed
Acta Botanica Brasilica - 34(1): 94-106. January-March 2020
95
Marileide Dias Saba, Gerleni Lopes Esteves, Valdira de Jesus Santos and Francisco de Assis Ribeiro dos Santos
Table 1. Species used in the morphological analysis of pollen grains of Bombacoideae. *Material used in photomicrographs and
electromicrographs.
Species
Voucher
Andrade-Lima 8145, Harley & Giulietti 54045,
Ceiba erianthos K. Schum
Guedes & Eudes 4839
Queiroz et al. 997, Oliveira 258, Lyra-Lemos et
C. glaziovii (Kuntze) K. Schum.
al. 7030
Eriotheca candolleana (K. Schum.) A. Robyns
Monteiro 23510, Pirani et al. 4356
E. gracilipes (K. Schum.) A. Robyns
Andrade-Lima 5491
E. macrophylla (K. Schum.) A. Robyns
Lima 12632, Ducke & Lima 65
E. obcordata A. Robyns
Silva et al. 107
Miranda 72, Fróes 26.629, Alunos de Taxonomia
Pachira aquatica Aubl.
da FUFPI s.n.
P. nervosa (Uitt.) A. Robyns
Esteves et al. 02
Freire-Fierro et al. s.n., Queiroz et al. 9634,
P. retusa (Mart. & Zucc.) Fern Alonso
Junqueira et al. 142
P. tocantina (Ducke) Fern. Alonso
Fróes 23378
Pseudobombax calcicola Carv.-Sobr. & L.P.Queiroz
Carvalho-Sobrinho & Queiroz 573
Ps. marginatum (A. St.-Hil., A. Juss. & Cambess.)
Castro s.n., Figueiredo et al. 175, Du Bocage 267
A Robyns
Ps. minimum Carv.-Sobr. & L.P.Queiroz
Forzza et al. 1591
Queiroz & Nascimento 4628, Queiroz et al. 7361,
Ps. simplicifolium A. Robyns
Du Bocage 274
Rhodognaphalopsis faroensis (Ducke) A. Robyns Ribeiro & Pereira 1704, Esteves & Assunção 07
in glutaraldehyde (2.5 %) with 0.1 M sodium phosphate
solution at pH 7.4, post-fixed in 1 % osmium tetroxide
(OsO4), dehydrated in an ascending acetone series (30, 50,
70, 90 and three baths at 100 % for 30 min each bath) and
included in EPON resin. Sections made using an Ultracut
E ultramicrotome equipped with a diamond razor were
contrasted with 7 % aqueous uranyl acetate and lead citrate
for observation using a Zeiss M 109 microscope of the
Electron Microscopy Laboratory of the Gonçalo Moniz
Research Center - Oswaldo Cruz Foundation.
The terminology adopted is in accordance with Punt
et al. (2007). The denomination ‘equatorial calotte’ is in
agreement with the definition of Robyns (1963).
Results
Pollen grains of the studied species of Bombacoideae
are characterized as medium to large in size, isopolar,
oblate to suboblate with a (sub)circular and (sub)triangular
amb (planaperturate) and a small to large polar area;
3-4-5(-6)-zonoaperturate, colpate, colporate, equatorial
calottes different or not, exine tectate-perforate to
microreticulate, reticulate with or without supratectal
processes and sexine thicker than nexine.
Table 2 summarizes the quantitative pollen characters
of the investigated specimens. Figures 1-5 illustrate
morphopalynous characteristics.
Ceiba erianthos (Cav.) K. Schum. (Fig. 1A-E); C. glaziovii
(Kuntze) K. Schum. (Fig. 1F-K)
Pollen grains large; oblate to suboblate; isopolar; amb
circular; 4-5(-6)-zonocolporate. Ectoapertures long with
sharp ends; endoapertures lalongate, circular or less frequent
lalongate; membrane psilate-aperturate. Exine semitectate,
96
Herbarium
IPA*, HUEFS, ALCB
HUEFS, HUEFS, HUEFS*
PEUFR*, SPF
IPA*
HST*, IPA
HUEFS
HUEFS, SP*, TEPB 450
SP*
SPF 106500*, HUEFS, HUEFS
SP*
HUEFS
EAC 32129, EAC, IPA*
HUEFS
HUEFS, HUEFS*, IPA
SP*, SP
reticulate, heterobrochate. Muri high, sinuous, simple to
dupli-columellate. Sexine thicker than nexine.
In addition to the 4-5-aperturate pollen grains,
6-aperturate pollen grains (Fig. 1A) were recorded in the
specimen Andrade-Lima 8145 of C. erianthos (ca. 6 %) and
in the specimen Oliveira 258 of C. glaziovii (ca. 11 %). The
endoaperture is difficult to visualize in C. erianthos; it was
lolongate in most specimens analyzed but specimens with
circular (Fig. 1H) or lalongate endapertures could also be
found.
The lumina of the reticulum are irregular, gradually
decreasing in size from the apocolpium to the mesocolpium;
free bacula and granules could be identified using SEM
(Fig. 1D; 1J). Branched muri of the reticulum supported
by oblique columellae could also be observed using SEM
(Fig. 1D, 1I, 1J).
The TEM analysis (Fig. 1E) of C. erianthos, which is the
first for the species, revealed stratification of the exine
consisting of a semitectum, which is as thick as the nexine
(referring to the basal layer plus endexine, layers which
were not discernible by the methodology used), supported
by short columellae, and the intine, which is thicker and
stratified under the apertures.
Eriotheca candolleana (K. Schum.) A. Robyns (Fig. 2A-E);
E. macrophylla (K. Schum.) A. Robyns (Fig. 2F-H); E. gracilipes
(K. Schum.) A. Robyns (Fig. 2I-J); E. obcordata A. Robyns
(Fig 2K-L)
Pollen grains medium to large in size; oblate; isopolar;
amb (sub)triangular with flat to convex sides; equatorial
calottes undifferentiated; 3(-4)-colporate; planaperturate.
Ectoapertures short and narrow with sharp ends;
endoapertures lolongate and lalongate; membrane psilateaperturate. Exine semitectate, reticulate, heterobrochate,
Acta Botanica Brasilica - 34(1): 94-106. January-March 2020
Morphological characterization of pollen grains of Brazilian species of Bombacoideae (Malvaceae s.l.)
Table 2. Pollen morphometric characteristics and measurements (μm) for species of Bombacoideae (Malvaceae s.l.): polar axis (P),
equatorial axis (E), equatorial axis in polar view (Epv), polar axis/equatorial axis (P/E), range (R), apocolpium index (AI), ectoaperture
length x ectoaperture width (Ec), endoaberture height (Eh), sexine (Sex), nexine (Nex), * n < 25.
Species / specimens
Ceiba erianthos
Guedes & Eudes 4839 (ALCB)
Harley & Giulietti 54045 (HUEFS)
Andrade-Lima 8145 (IPA)
C. glaziovii
Queiroz et al. 997 (HUEFS)
Lyra-Lemos et al. 7030 (HUEFS)
Oliveira 258 (HUEFS)
Eriotheca candolleana
Monteiro 23510 (PEUFR)
Pirani et al .4356 (SPF)
E. gracilipes
Andrade-Lima 5491 (IPA)
E. macrophylla
Lima 12632 (HST) (3-apert)
Lima 12632(HST) (4-apert)
Ducke & Lima 65 (IPA)
E. obcordata
Silva et al. 107 (HUEFS)
Pachira aquatica
Fróes 26629 (SP)
Alunos Taxonomia da FUFPI s.n.
(TEPB450)
Miranda 72 (HUEFS)
P. nervosa
Esteves et al. 02 (SP)
P. retusa
Freire-Fierro et al. s.n. (SPF106500)
Junqueira et al. 142 (HUEFS)
Queiroz et al. 9634 (HUEFS)
P. tocantina
Fróes 23378 (SP)
Pseudobombax calcicola
Carvalho-Sobrinho & Queiroz 573
(HUEFS)
Ps. marginatum
Castro s.n. (EAC32129)
Du Bocage 267 (IPA)
Figueiredo et al. 175 (EAC)
Ps. minimum
Forzza et al. 1591 (HUEFS)
Ps. simplicifolium
Queiroz & Nascimento 4628 (HUEFS)
Du Bocage 274 (IPA)
Queiroz et al. 7361 (HUEFS)
Rhodognaphalopsis faroensis
Ribeiro & Pereira 1704 (SP)
Esteves & Assunção 07 (SP)
P
E
Epv
R
AI
Ec
Eh
Sex Nex
R
X±SX
46.1*
42.1*
38.6*
43.5-52.5
39.0-45.0
36.0-43.5
55.5*
60.5*
52.9*
46.5-63.0 57.6±1.1 46.5-67.5 0.83 0.44 23.6x1.0 ─ 2.1 1.7
55.5-64.5
57.8*
52.5-64.5 0.70 0.46 21.9x4.1 7.8 2.0 1.2
51.0-54.0
64.4*
52.5-70.5 0.73 0.42 15.5x4.8 ─ 1.7 0.7
47.8*
44.8*
46.5*
42.5-51.3
42.0-49.5
43.5-48.0
58.8*
57.8*
57.5*
53.8-63.8
56.0*
50.0-66.3 0.81 0.47 14.9x2.7 5.0 2.7 0.8
54.0-63.8
56.9*
52.5-61.5 0.77 0.53 16.9x4.2 5.3 2.5 0.9
55.5-60.0 58.6±0.5 52.5-63.0 0.81 0.47 16.7x3.6 7.1 3.2 1.0
X±SX
R
P/E
X±SX
28.8±0.4 25.0-32.5 43.7±0.6 40.0-50.0 41.5±0.6 37.5-47.5 0.66 0.65 10.9x2.3 4.0 1.7 0.6
24.0* 20.0-27.5
34.5*
32.5-36.2 33.1±0.5 32.1-34.0 0.69 0.59 7.2x1.0 2.5 1.7 0.7
27.8±0.3 25.5-30.0 38.0±0.4 31.5-42.0 36.7±0.4 31.5-40.5 0.73 0.55 12.3x1.5 4.7 1.6 0.9
22.0±1.0 18.0-27.0 41.3±1.8 39.0-46.5 42.7±0.5 39.0-49.5 0.53 0.57
42.1±0.4 39.0-45.0 ─ 0.55
─
─
─
─
28.6* 25.0-33.8
41.5*
33.8-45.0 36.8±1.6 33.8-45.0 0.69 0.64
9.8x2.4
─
9.0x2.4
4.3 1.5 0.6
─ 1.4 0.6
4.5 1.1 0.6
30.1±0.5 27.0-33.0 44.2±0.6 40.5-52.5 42.7±0.6 37.5-48.0 0.68 0.60 11.9x2.0 5.4 1.4 0.7
56.3±0.4 52.5-60.0 69.1±0.5 63.0-73.5 66.0±0.8 57.0-70.5 0.81 0.62 17.9x3.5 7.9 1.8 1.2
─
─
─
49.0*
40.5-55.5
60.6*
52.5-67.5 59.1±0.7 52.5-67.5 0.81 0.65 20.9x5.4 10.5 1.2 1.1
38.2*
33.0-43.5
62.2*
60.0-66.0 57.8±0.5 52.5-63.0 0.61 0.54 13.9x3.1 5.3 1.8 0.6
46.6*
48.3*
46.0*
42.0-51.0
45.0-52.5
45.0-46.5
64.0*
66.3*
64.5*
60.0-70.5
58.2*
48.0-63.0 0.73 0.56 14.7x4.1 7.8 1.5 0.6
60.0-72.0 61.4±1.0 49.5-75.0 0.73 0.56 13.2x3.4 ─ 1.1 0.6
63.0-67.5
60.2*
54.0-64.5 0.71 0.60 17.4x2.4 ─ 1.1 0.6
45.3*
39.0-52.5
64.6*
57.0-70.5 60.7±0.8 49.5-69.0 0.70 0.56 12.6x2.2
─
2.3 0.6
52.9±0.9 45.0-65.0 90.8±0.7 82.5-100.0 79.9±0.8 70.0-87.5 0.58 0.51 23.3x4.7
─
1.7 1.2
─
41.0*
39.0*
─
37.5-45.0
37.5-40.5
─
64.0*
73.5*
─
─
63.0-64.5
67.5-79.5
61.2*
62.4*
62.5*
63.4*
58.5-63.0
─
0.61 14.2x3.3 6.2 1.4 1.0
58.5-66.0 ─ 0.57 17.8x2.0 7.0 1.7 0.8
55.5-70.5 0.64 0.54 24.0x6.0 15.6 1.6 0.9
54.0-76.5 0.53 0.53 18.5x3.4 ─ 1.6 0.7
42.4±0.8 32.5-50.0 61.3±0.5 57.5-67.5 57.2±0.7 52.5-67.5 0.69 0.53 20.1x3.1
─
1.5 0.7
38.8* 34.5-45.0
62.5*
58.5-67.5 61.2±1.1 48.0-69.0 0.62 0.42 20.6x5.4
42.1* 30.0-50.0
65.4*
56.3-78.8 61.8±1.1 50.0-71.3 0.64 0.40 22.4x2.4
39.0±0.5 33.0-43.5 61.0±0.9 49.5-70.5 57.0±0.8 48.0-63.0 0.64 0.47 22.1x5.3
─
─
─
1.9 0.6
1.9 0.6
1.7 0.6
42.1±0.4 39.0-45.0 58.9±0.6 48.0-63.0 53.8±0.6 46.5-60.0 0.71 0.62 13.0x2.2 4.7 1.3 0.9
38.6±0.8 33.0-48.0 ─ 0.60
─
─
─
─
─
─ 1.4 0.6
lumina polyhedral with free granules in the interior; muri high,
smooth and simplicolumellate. Sexine thicker than nexine.
The pollen grains of species of Eriotheca are uniform
in size (Tab. 2). The largest pollen grains (52.5 μm) were
observed for E. obcordata; however, the average size class
was predominant among the analyzed specimens. The amb
varied between subtriangular and triangular, with the latter
predominating. The 4-aperturate pollen grains (Fig. 2F) had
a subcircular amb. 4-aperturate pollen grains were recorded
in one specimen of E. candolleana (Monteiro 23510) and for
Acta Botanica Brasilica - 34(1): 94-106. January-March 2020
97
Marileide Dias Saba, Gerleni Lopes Esteves, Valdira de Jesus Santos and Francisco de Assis Ribeiro dos Santos
Figure 1. Pollen grains of species of Ceiba Mill. A-E. C. erianthos K. Schum. A. Optical section in polar view. B. LO-analysis. C. Optical
section in equatorial view. D. Surface detail (SEM). E. Detail of murus structure in cross-section (SEM). F-L. C. glaziovii (Kuntze) K.
Schum. F. Optical section in polar view. G. LO-analysis. H. Detail of aperture and surface. I. Polar view (SEM). J. Surface detail (SEM).
K. Aperture detail (SEM). (t = tectum, c = columella, b = basal layer, i = intine)
98
Acta Botanica Brasilica - 34(1): 94-106. January-March 2020
Morphological characterization of pollen grains of Brazilian species of Bombacoideae (Malvaceae s.l.)
Figure 2. Pollen grains of species of Eriotheca Schott & Endl. A-E. E. candolleana (K. Schum.) A. Robyns- A. Optical section in polar
view. B. LO-analysis. C. Aperture and surface in equatorial view. D. Polar view (SEM). E. Surface detail (SEM). F-H. E. macrophylla
(K. Schum.) A. Robyns- F. Optical section in polar view. G. LO-analysis. H. Detail of aperture (SEM). I-J. E. gracilipes (K. Schum.) A.
Robyns- I. Polar view (SEM). J. Surface detail (SEM). K-L. E. obcordata A. Robyns. K. Optical section in polar view. L. LO-analysis.
Acta Botanica Brasilica - 34(1): 94-106. January-March 2020
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Marileide Dias Saba, Gerleni Lopes Esteves, Valdira de Jesus Santos and Francisco de Assis Ribeiro dos Santos
specimens of E. macrophylla; however, the specimen Lima
12632 had the most significant percentage of 4-aperturate
pollen grains with 12.7 %, while other specimens had 2 % or
less. All specimens analyzed of E. gracilipes had 3-aperturate
pollen. The ectoapertures were short and narrow, sometimes
hindering visualization of endoapertures under LM, which
was characterized as lolongate in E. candolleana, E. gracilipes
and E. macrophylla, and lalongate with straight to concave
upper and inferior margins in E. obcordata. Using SEM, it
was possible to detect the presence of heterogeneouslysized granules in the reticulum lumina of the specimens
analyzed (Fig. 2J). The smooth surface of muri was also
observed with SEM.
Pachira aquatica Aubl. (Fig. 3A-D); P. nervosa (Uitt.)
Fernández-Alonso (Fig. 3E-F); P. retusa (Mart. &Zucc.)
Fernández-Alonso (Fig. 3G-J); P. tocantina (Ducke)
Fernández-Alonso (Fig. 3K-L)
Pollen grains large; oblate to suboblate; isopolar; amb
triangular, less frequently quadrangular, with flat to slightly
convex sides; equatorial calottes separate, protrusions
with rounded angles; planaperturate; 3-colp(or)ate,
sometimes 4-colporate; costate and with differentiated
margin. Ectoapertures short with sharp ends; endoapertures
lolongate, sometimes difficult to visualize. Exine reticulate
and heterobrochate in the polar and apertural regions,
psilate-perforate, microreticulate in the equatorial calottes.
Muri thin to wide, simplicolumellate to duplicolumellate,
with simple and digitate columellae, anastomosed, with
supratectal protrusions. Sexine thicker than nexine.
Morphologically, the pollen grains of the studied
species of Pachira are similar. There was a predominance
of 3-aperturate pollen grains; 4-colporate (7 %) pollen
grains were found only in the examined specimen of
P. nervosa. The aperture was well defined in P. aquatica,
with a margin devoid of ornamentation (Fig. 3D); the
aperture was difficult to visualize in the other species
using LM, with continuous ornamentation up to the
apertural region, without a differentiated margin. The
endoapertures were lolongate with an irregular outline,
and were difficult to visualize in some of the analyzed
specimens. It was not possible to measure the endoaperture
of all of the analyzed specimens of P. retusa, since most
pollen grains were kneaded making it difficult to visualize
the endoaperture (Fig. 3H). The surface of pollen grains had
reticulate ornamentation in polar and apertural regions,
with irregular lumina and ornate muri, but differing in the
equatorial calottes where it was psilate-perforate (SEM).
There were concentrated perforations towards the reticulate
regions (Fig. 3C-D) in P. aquatica, and microreticulate in
the other species (Fig. 3E).
The SEM examination revealed longitudinally-elongated
supratectate protrusions, with predominantly rounded
apices, starting from the point of intersection of the
reticulate muri in P. aquatica (Fig. 3C, 3D), characterizing
100
a “cristate reticulum” sensu Hesse et al. (2009). In the other
species, the branched columellae (Fig. 3J, L) fuse distally,
forming supratectate structures of varied shapes (Fig. 3F, I).
Granules were observed by SEM inside the lumina of P.
nervosa (Fig. 3F). The sexine was thicker than the nexine in
all specimens (Tab. 2), with the largest difference being for
a specimen of P. tocantina, for which the sexine measured
2.3 μm and the nexine measured 0.6 μm.
Pseudobombax calcicola Carv.-Sobr. & Queiroz LP (Fig.
4A-E); Ps. marginatum (A. St.-Hil., A. Juss. & Cambess.) A.
Robyns (Fig. 4F-I); Ps. minimum Carv.-Sobr. & LP Queiroz
(Fig. 4J-N); Ps. simplicifolium A. Robyns (Fig. 4O-Q)
Pollen grains large, oblate, isopolar; amb triangular
with flat to slightly concave sides; equatorial calottes
slightly to very evident, with rounded angles; 3-colp(or)ate;
planaperturate; costate. Ectoapertures short and long with
rounded ends; endoapertures lolongate when present. Exine
reticulate, heterobrochate, with circular to elongated lumina
in the polar region and around the apertures with granules
in the interior, psilate, granulate and microreticulate in
the mesocolpium region and colpus margin. Muri wide,
smooth and perforated, single-, dupli- or less frequent
pluricolumellate, with distinct columellae using optical
(LM), and short and wide columellae using SEM. Sexine
thicker than nexine.
The pollen grains of most of the analyzed species
were homogeneous in shape, size and amb, with the
exception of Ps. calcicola, which reached a size of up to
100 μm (Tab. 2).
As for apertures, colporate pollen grains were observed
in Ps. marginatum, Ps. simplicifolium and Ps. minimum, but
it was not possible to measure the endoapertures in any
of the analyzed specimens of the latter two species. The
endoaperture was characterized as circular or lolongate in
most of the analyzed specimens, but difficult to visualize
using light microscopy (Fig. 4H, 4O). A differentiated margin
was noted using SEM (Fig. 4I). The pollen grains of specimen
Figueiredo et al. 175 of Ps. marginatum and the analyzed
specimen of Ps. calcicola were characterized as colpate.
The ornamentation of the exine is reticulate with circular
to elongated lumina in the polar region and around the
apertures. Using SEM, the exine was observed to be psilate
in the equatorial calotte in Ps. Calcicola and Ps. Simplicifolium,
finely granulate and irregularly perforate in Ps. Marginatum,
and microreticulate in Ps. Minimum. The reticulum of Ps.
minimum had comparatively smaller lumina, uniform up to
the apertural region, without a differentiated margin (Fig. 4L).
With SEM it was possible to observe few and spaced
perforations in the reticulum muri (Fig. 4L, M, Q). Figures
4E and 4N show how the tectum is supported by large and
short columellae that form single rows, double rows or more
rarely several rows (Fig. 4G) under the muri.
The sexine was much thicker than nexine in all the
studied species. Using SEM, short columellae and the
Acta Botanica Brasilica - 34(1): 94-106. January-March 2020
Morphological characterization of pollen grains of Brazilian species of Bombacoideae (Malvaceae s.l.)
Figure 3. Pollen grains of Pachira Aubl. A-D. P. aquatica Aubl.- A. Optical section in polar view. B. Optical section in equatorial view.
C. Polar view (SEM). D. Detail of surface and aperture (SEM). E-F. P. nervosa (Uitt.) Fernández-Alonso- E. Polar view (SEM). F. Detail
of aperture (SEM). G-J. P. retusa (Mart & Zucc.) Fernández-Alonso- G. Optical section in polar view. H. Optical section in equatorial
view. I. Surface detail (SEM). J. Structure of exine with forked columella (arrow) (SEM). K-L. P. tocantina (Ducke) Fernández-AlonsoK. Polar view (SEM). L. Structure of exine with forked columellae (arrows) (SEM).
Acta Botanica Brasilica - 34(1): 94-106. January-March 2020
101
Marileide Dias Saba, Gerleni Lopes Esteves, Valdira de Jesus Santos and Francisco de Assis Ribeiro dos Santos
Figure 4. Pollen grains of species of Pseudobombax Dugand. A-E. Ps. calcicola Carv.-Sobr. & L.P. Queiroz - A. Optical section in polar
view. B. LO-analysis C. Optical section in equatorial view. D. Polar view (SEM). E. Structure of exine (SEM). F-I. Ps. marginatum (A.
St.-Hil., A. Juss. & Cambess.) A. Robyns- F. Optical section in polar view. G. Analysis of L.O. H. Aperture and surface in equatorial
view. I. Detail of aperture (SEM). J-N. Ps. minimum Carv.-Sobr. & L.P. Queiroz - J. Optical section in polar view. K. LO-analysis
L. Detail of aperture (SEM). M. Surface detail (SEM). N. Structure of exine (SEM). O-Q. Ps. simplicifolium A. Robyns- O. Optical section
in equatorial view, detail of the aperture in the upper right corner (SEM). P. Polar view (SEM). Q. Surface detail (SEM).
inner surface of the rough nexine could be observed for Ps.
minimum (Fig. 4N) and an undulate nexine for Ps. calcicolate
(Fig. 4E).
Rhodognaphalopsis faroensis (Ducke) A. Robyns
(Fig. 5A-G)
Pollen grains large; oblate; isopolar; amb triangular
with concave sides; 3-colporate; costate. Ectoapertures
short with rounded ends; endoapertures lalongate with
concave upper and lower margins. Exine microreticulate-
102
echinate using LM, tectate-perforate with supratectate
protrusions with cylindrical and conical shapes and
heterogeneous sizes and diameters using SEM. Sexine
thicker than nexine.
The ectoapertures were observed to be short, narrow,
with a regular outline and rounded ends, and without a
differentiated margin using LM and SEM (Fig. 5C, G). The
endoaperture was lalongate with concave upper and lower
margins while the extremeties were difficult to view. Figure 5D
shows the costae of the pollen grains of the studied species.
Acta Botanica Brasilica - 34(1): 94-106. January-March 2020
Morphological characterization of pollen grains of Brazilian species of Bombacoideae (Malvaceae s.l.)
Figure 5. A-G. Pollen grains of Rhodognaphalopsis faroensis (Ducke) A. Robyns- A. Optical section in polar view. B. LO-analysis.
C. Detail of aperture. D. Optical section of aperture. E. Polar view (SEM). F. Surface detail (SEM). G. Equatorial View (SEM).
LO-analysis (Fig. 5B) revealed a tectum with a pattern
similar to that of a microreticulum. Higher amplifications
using SEM, however, revealed the presence of perforations
of varied diameter and shape (spherical and elongated)
concentrated in the polar region. The supratectate
protrusions also varied in shape and diameter, with
cylindrical protrusions with rounded ends and conical
protrusions with a sharp end (Fig. 5E-G).
Principal component analysis
The first two axes of the PCA explained 85.43 % of the
total variance (Fig. 6). The first axis (PC1) explained 75.66 %
of the total variance with ectoaperture length (EcL) and
width (EcW) being the most significant variables, followed
equatorial diameter in polar view (E) (Tab. 3). The species
of Pseudobombax (Ps. calc, Ps. simp, Ps. marg, Ps. mini) and
Paquira aquatica (Pa. aqua) were grouped having the highest
values for these variables of the first axis. In contrast,
species of Eriotheca (Er. macr, Er. obco, Er. cand, Er. grac.)
were grouped on the opposite side with lower values of E,
EcL and EcW. The second axis (PC2) explained 9.77 % of
the total variance, with sexine (Sex) and exine (Ex) being
the most significant variables (Tab. 3). The variables polar
area index (AI) and nexine (Nex) were correlated with the
second axis. The taxa in the bottom left quadrant have
lower values for AI (Fig. 6).
Acta Botanica Brasilica - 34(1): 94-106. January-March 2020
103
Marileide Dias Saba, Gerleni Lopes Esteves, Valdira de Jesus Santos and Francisco de Assis Ribeiro dos Santos
Figure 6. Principal component analysis performed with the
pollen metrical variables of Brazilian species of Bombacoideae.
Ce. eria = Ceiba erianthos, Ce glaz = C. glaziovii, Er. cand = Eriotheca
candolleana, Er. grac = E. gracilipes, Er. macr = E. macrophylla, Er.
obco = E. obcordata, Pa. aqua = Pachira aquatica, Pa. nerv = P. nervosa,
Pa. retu = P. retusa, Pa. toca = P. tocantina, Ps. calc = Pseudobombax
calcicola, Ps. marg = Ps. marginatum, Ps. mini = Ps. minimum, Ps.
simp = Ps. simplicifolium, Rh. faro = Rhodognaphalopsis faroensis.
Table 3. Pearson and Kendall correlation coefficients for pollen
metrical variables of the first and the second axis of PCA ordination
of species of Bombacoideae.
Variables
P
E
Epv
P/E
AI
EcL
EcW
Ex
Sex
Nex
Principal components
Axis 1
Axis 2
-0.4097
-0.0667
-0.4249
0.1661
-0.4106
0.0164
0.0032
-0.0982
0.0400
0.0757
-0.4951
0.0199
-0.4555
0.1916
-0.1122
-0.6455
-0.0712
-0.6666
-0.1054
-0.2328
Discussion
Data reported in the literature for other species of Ceiba
have revealed that, in addition to having a reticulum and
gems and piles, sculptural elements such as the exine may
also be present (Erdtman 1952; Palacios-Chavez et al. 1991).
Using SEM, Nilson & Robyns (1986) described for this
genus the presence of clava or bacula-like processes in the
reticulum lumina, in addition to ramified muri supported by
oblique columellae, as was corroborated by the present study.
Abreu et al. (2014) also recorded elements of ornamentation
in the lumina of C. erianthos.
104
The results obtained in this research regarding aperture
type are in agreement with data found in the literature
for this genus, except for the number of apertures. The
3-aperture condition cited by Erdtman (1952), Tsukada
(1964), Sowunmi 1973), Nilson & Robyns (1986), PalaciosChavez et al. (1991), Moncada & Sotolongo (1994), Carreira
et al. (1995), and Abreu et al. (2014) for other species of the
genus, was not observed in any of the specimens analyzed
here.
There are no data in the literature on the ultrastructure
of pollen grains of other species of Bombacoideae. However,
some of the data presented here for Ceiba erianthos (e.g.,
short columellae and thicker intine at the apertural region)
are in agreement with those reported for other species of
Malvaceae s.l. (Saba & Santos 2015; Silveira-Júnior et al.
2015; 2017).
Robyns (1963) and Salgado-Labouriau (1973) described
the pollen grains of the species of Eriotheca studied here
and reported similar pollen characteristics. However,
these authors referred to duplicolumellate muri, rarely
pluricolumellate, for E. candolleana (Robyns 1963) and
E. gracilipes (Robyns 1963; Salgado-Labouriau 1973).
Furthermore, the colpate pollen grains described by
Robyns (1963) for E. macrophylla (crenulaticalyx) are not
in accordance with the data presented here. Visualization
of the endoaperture is very difficult by LM, but the SEM
analysis of the present work was able to confirm its
presence.
For Nilson & Robyns (1986), species of Eriotheca,
including the species studied here, along with species of
the genera Aguiaria , Pachira (Bombacopsis), Pseudobombax
and Spirotheca, comprise the Bombax pollen type. The data
presented here are in agreement with those presented by
these authors with the exception of the pattern of rugulate
ornamentation of the exine, which was not observed in any
of the species analyzed here. Abreu et al. (2014) recorded
perforations in the reticulum muri of E. pentaphylla,
which were not observed in the present study. The other
characteristics reported by Abreu et al. (2014) are consistent
with the data presented here.
Robyns (1963) and Salgado-Labouriau (1973) described
the pollen grains of Pachira retusa and P. tocantina as colpate
and colporate, respectively. These data differ from those
presented here, which may be explained by the lolongate
type of endoapertures, which was difficult to visualize in
the analyzed species, and by the kneaded condition of the
majority of pollen grains after acetolysis. The authors did
not mention the presence of costae, as evidenced here for
P. nervosa.
Robyns (1963) and Moncada & Sotolongo (1994) using
LM, and Carreira et al. (1995) using SEM, reported the
presence of spines in equatorial calottes. Such elements were
not observed in any of the specimens analyzed here. The
equatorial calottes of the analyzed specimens of P. tocantina
were less prominent than those of the other studied species.
Acta Botanica Brasilica - 34(1): 94-106. January-March 2020
Morphological characterization of pollen grains of Brazilian species of Bombacoideae (Malvaceae s.l.)
Specialized literature includes references of pollen
grains with spinous processes for the species studied here
(Robyns 1963; Tsukada 1964; Nilson & Robyns 1986;
Moncada & Sotolongo 1994) as well as for other species
of Pachira (Salgado-Labouriau 1973; Nilson & Robyns 1986;
Bove 1993). Supratectate protrusions were observed for
the species studied here, but they were not considered
spinous processes. Carreira et al. (1995) did not refer to
such structures.
The species of Pachira studied by Nilson & Robyns
(1986) were included in the Bombax pollen type, which is
characterized as 3(-4)-colp(or)ate, rarely porate, reticulate,
microreticulate to rarely tectate-perforated, equinate, and
rarely rugulate. Most of the pollen traits presented by these
authors were corroborated by the present study, with the
exception of the presence of equinate and rugulate pollen
grains, which was not observed in the specimens analyzed
here.
The occurrence of colpate and colporate pollen grains
in the same species of Pseudobombax was reported in the
literature by Robyns (1963) and Salgado-Labouriau (1973)
using LM. Considering the difficulty of visualizing the
endoaperture using LM, identifications of apertural type
in some of the descriptions presented for species of this
genus may be mistaken.
According to Nilson & Robyns (1986), in addition to
the presence of a reticulum and microreticulum, rugulae
can also be present as sculptural elements of pollen grains
of species of Pseudobombax. Pollen data in the literature
for Ps. simplicifolium and Ps. marginatum (Robyns 1963;
Salgado-Labouriau 1973; Nilson & Robyns 1986; Abreu et
al. 2014), and for other species of the genus (Tsukada 1964;
Melhem & Bissa 1985; Bove 1993; Moncada & Sotolongo
1994), were corroborated by the present study.
Data reported in the literature (Robyns 1963;
Nilson & Robyns 1986) on the pollen morphology of
Rhodognaphalopsis are consistent those of presented
here for most morphopalynous characters. However, the
4-aperturate and colpate type of aperture described by
Nilson & Robyns (1986), and the type of endoaperture
observed by Robyns (1963) and Nilson & Robyns (1986),
were not observed in any of the specimens analyzed here.
The data obtained in the present study confirmed the
heterogeneous nature of the pollen of representatives of
Bombacoideae. Ornamentation type was found to be an
important character for recognizing the studied species
of this subfamily. Rhodognaphalopsis differs by having
perforate to microreticulate pollen grains with cylindrical
and conical supratectate protrusions, while other genera
have a foveolate sexine. Pseudobombax and Pachira both have
pollen grains with differentiated equatorial calottes, as well
as a triangular amb and a planaperture-type of aperture,
however, the reticulum of the analyzed species of these
genera differs. The ordering of species by PCA confirmed
the separation of the studied species of Bombacoideae
using only quantitative variables of the pollen grains. Some
attributes show potential usefulness for characterizing
species, such as equatorial diameter and sexine thickness.
In conclusion, morphological and morphometric pollen data
provided useful information for distinguishing the studied
species, and can contribute substantially to understanding
the diversity and relationships among genera and species
of the subfamily Bombacoideae.
Acknowledgements
The authors would like to thank the curators of herbaria
for authorizing the collection of botanical material;
researchers Marcos André Vannier and Cláudio Pereira
from the Centro de Pesquisa Gonçalo Muniz - Instituto
Oswaldo Cruz (FIOCRUZ), for authorizing and assisting
with SEM analysis; and CNPq for research support to FARS.
References
Abreu VHR, Mendonça CBF, Gonçalves-Esteves V. 2014. Pollen morphology
of selected species of the subfamily Bombacoideae (Malvaceae sensu
lato). Acta Botanica Brasilica 28: 352-360.
Alverson WS, Whitlock BA, Nyffeler R, Bayer C, Baum DA. 1999. Phylogeny
of the core Malvales: evidence from ndhF sequence data. American
Journal of Botany 86: 1474-1486.
Baum DA, Smith SD, Yen A, et al. 2004. Phylogenetic relationships of
Malvatheca (Bombacoideae and Malvoideae; Malvaceae sensu lato)
as inferred from plastid DNA sequences. American Journal of Botany
91: 1863-1871.
Bayer C, Fay MF, Bruijn AY, et al. 1999. Support for an expanded family
concept of Malvaceae within a recircunscribed order Malvales: a
combined analysis of plastid atpB and rbcL DNA sequences. Botanical
Journal of the Linnean Society 129: 267-303.
Bove CP. 1993. Catálogo sistemático do pólen das plantas arbóreas do
Brasil meridional – XXVII – Bombacaceae, Caprifoliaceae e Sytracaceae.
Revista Brasileira de Biologia 53: 87-101.
Braga RP. 1960. Plantas do Nordeste, especialmente do Ceará. 4th. edn.
Natal, Ed. Universitária UFRN.
Candolle AP. 1824. Bombacaceae. Prodromus Systematis Naturalis Regni
Vegetabilis. Vol. 1. Paris, Caprelet.
Carreira LMM, Raposo RCO, Lobato ESP. 1995. Morfologia polínica
de plantas cultivadas no Parque do Museu Goeldi. VII – Família
Bombacaceae. Boletim do Museu Paraense Emílio Goeldi, Série
Botânica 11: 275-293.
Carvalho-Sobrinho JG, Alverson WS, Alcantara S, Queiroz LP, Mota
AC, Baum D A. 2016. Revisiting the phylogeny of Bombacoideae
(Malvaceae): Novel relationships, morphologically cohesive clades, and
a new tribal classification based on multilocus phylogenetic analyses.
Molecular Phylogenetics and Evolution 101: 56-74.
Cronquist A. 1981. An integrated system of classification of flowering
plants. New York, Columbia University Press.
Erdtman G. 1952. Pollen morphology and plant taxonomy – angiosperms.
Stockholm, Almqvist and Wiksell.
Erdtman G. 1960. The acetolysis method. A revised description. Svensk
Botanisk Tidskrift 54: 561-564.
Fuchs HP. 1967. Pollen morphology of the family Bombacaceae. Review
of Palaeobotany and Palynology 3: 119-132.
Hesse M, Halbritter H, Zetter R, et al. 2009. Pollen terminology: an
illustrated handbook. Wien, Springer-Verlag.
Kunth KS. 1821. Bombacaceae. In: Humbold A, Bonpland A, Kunth KS.
(eds.) Nova genera et species plantarum. Vol. 5. Antverpiae, Ex officina
Christophori Plantini. p. 294-308.
Acta Botanica Brasilica - 34(1): 94-106. January-March 2020
105
Marileide Dias Saba, Gerleni Lopes Esteves, Valdira de Jesus Santos and Francisco de Assis Ribeiro dos Santos
Lorenzi H. 2002a. Árvores brasileiras: manual de identificação e cultivo de
plantas arbóreas nativas do Brasil. Vol. 1. Nova Odessa, Ed. Plantarum.
Lorenzi H. 2002b. Árvores brasileiras: manual de identificação e cultivo
de plantas arbóreas nativas do Brasil. Vol. 2. Nova Odessa, Ed.
Plantarum.
Lozano-García MS, Hernández EM. 1990. Palinologia de la Estación de Biología
Tropical Los Tuxtlas: Parte I – especies arbóreas. México, Instituto de
Geologia, UNAM – Universidad Nacional Autónoma de México.
Maia GN. 2004. Caatinga: árvores e arbustos e suas utilidades. São Paulo,
D & Z Computação Gráfica e Editora.
McCune B, Mefford MJ. 2011. PC-ORD. Multivariate analysis of ecological
data. Version 5. Gleneden Beach, MjM Software.
Melhem TS, Bissa WM. 1985. Flora polínica da reserva do parque Estadual
das Fontes do Ipiranga (São Paulo, Brasil). Famílias: 35-Dilleniaceae,
38-Theaceae e 46-Bombacaceae. Hoehnea 12: 5-9.
Moncada M, Sotolongo L. 1994. Morfología de los granos de polen en
géneros de Bombacaceae en Cuba. Acta Botánica Cubana 97: 1-7.
Nilson S, Robyns A. 1986. Bombacaceae Kunth. World Pollen and Spore
Flora 14:1-59.
Nyffeler R, Bayer C, Alverson WS. et al. 2005. Phylogenetic analysis of the
Malvadendrina clade (Malvaceae s.l.) based on plastid DNA sequences.
Organisms, Diversity & Evolution 5: 109-123.
Palacios-Chávez R, Ludlow-Wiechers B, Villanueva RG. 1991. Flora
palinologica de la reserva de la biosfera de Sian Ka’an Quintana Roo,
Mexico. Chetumal, Centro de Investigações de Quintana Roo.
Punt W, Hoen PP, Blackmore S, Nilson S, Thomas A. 2007. Glossary of
pollen and spore terminology. Review of Palaeobotany and Palynology
143: 1-81.
106
Robyns A. 1963. Essai de Monographie du genre Bombax L. s.l.
(Bombacaceae). Bulletin du Jardin Botanique de l’État à Bruxelles
33: 1-311.
Robyns A. 1971. On pollen morphology of Bombacaceae. Bulletin du
Jardin Botanique National de Belgique 41: 451-456.
Saba MD, Santos FAR. 2015. Pollen morphology and exine ultrastructure
of selected species of Waltheria L. (Byttnerioideae-Malvaceae). Review
of Palaeobotany and Palynology 221: 204-210.
Salgado-Labouriau ML. 1973. Contribuição à palinologia dos cerrados.
Rio de Janeiro, Academia Brasileira de Ciências.
Silveira-Júnior CEA, Lima LLC, Saba MD. 2015. Palynological study of
heterostylous species of Melochia L. (Byttinerioideae-Malvaceae)
occurring in Bahia, Brazil. Review of Palaeobotany and Palynology
221: 192-203.
Silveira-Júnior CEA, Lima LLC, Saba MD. 2017. Pollen morphology of
Waltheria L. (Malvaceae-Byttnerioideae) from Bahia, Brazil. Acta
Botanica Brasilica 31: 597-612.
Sowunmi MA. 1973. Pollen grains of Nigerian plants. I. Woody species.
Grana 13: 145-186.
Stevens PF. 2005. Angiosperm Phylogeny Website. Version 6. May 2005.
http://www.mobot.org/MOBOT/research/APweb/. 26 Jul. 2018.
Thiers B. 2017. [continuously updated]. Index Herbariorum: a global directory
of public herbaria and associated staff. New York Botanical Garden’s
Virtual Herbarium. http://sweetgum.nybg.org/ih/. 15 Nov. 2018.
Tsukada M. 1964. Pollen morphology and identification III. Modern
and fossil tropical pollen with emphasis on Bombacaceae. Pollen et
Spores 6: 393-462.
Acta Botanica Brasilica - 34(1): 94-106. January-March 2020