Palynological Contribution to the Systematics and Taxonomy of Bauhinia S.L

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SAJB-01002; No of Pages 8 South African Journal of Botany xxx (2013) xxx–xxx

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South African Journal of Botany

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Palynological contribution to the systematics and taxonomy of Bauhinia s.l. (Leguminosae: Cercideae)

Hannah Banks a,⁎,FélixForesta, Gwilym Lewis b a Jodrell Laboratory, Royal Botanic Gardens, Kew, Richmond, Surry, TW9 3DS, UK b Herbarium, Library, Arts and Archives, Royal Botanic Gardens, Kew, Richmond, Surry, TW9 3AB, UK article info abstract

Available online xxxx Pollen grains of 250 samples of taxa in the Cercideae clade have been studied using light microscopy, scanning electron microscopy and transmission electron microscopy. This study examines how pollen morphological Edited by BE Van Wyk structures can be used as taxonomic characters in systematic studies. Pollen grains of the first branching taxa in the Cercideae phylogeny, such as Cercis and Adenolobus, are unspecialised; they are isopolar, tectate, Keywords: tricolporate, and released in monads. Surface ornamentation may be micro-reticulate or perforate, and psilate Bauhinia to rugulate. Aperture membranes are granular to coarsely granular. More specialised pollen grain structures Cercideae are found in Schnella, Lasiobema, Phanera, Piliostigma and most of Bauhinia s.s. Pollen morphology is presented Pollen Systematics in a table for comparative purposes and illustrated, discussed and compared. Six specialised pollen structures described and identified are diagnostic for groups of related species in the Cercideae. These include a granular infratectum, syncolporate apertures, pororate apertures, spiny opercula, tetrads, and non-supratectal spines. Porate apertures occur in Phanera, Piliostigma and Bauhinia picta. Five pollen structures have been identified within the Cercideae clade that is restricted to Bauhinia s.s. These include striate ornamentation, having more than three apertures per grain, apertures that are indistinct, and colpate apertures. Supratectal ornamentation, structures such as gemmae, verrucae and striae, occur in many species in the Cercideae, as well as throughout subfamily Caesalpinioideae, and the functional implications of this are discussed. Pollen morphological structures are discussed with regard to systematic significance, taxonomic utility, and in relation to functional and develop- mental considerations. © 2013 SAAB. Published by Elsevier B.V. All rights reserved.

1. Introduction phylogeny (Sinou et al., 2009), we are now able to better interpret the significance of the distribution of pollen structures within tribe Tribe Cercideae, which contains Bauhinia sensu lato, forms one of Cercideae, and to assess morphological variation in a systematic the first branching lineages in the Leguminosae. Many analyses, based context. The aims of this study are to identify pollen characters that on both morphological (Wunderlin et al., 1987; Zhang, 1995)and are putative synapomorphies for segregates of Bauhinia s.l.,aswellas molecular characters (Bruneau et al., 2001, 2008; Hao et al., 2003; to examine the evolution of pollen structures within the group. Lewis and Forest, 2005), show different relationships between taxa in the Cercideae. The taxonomic history of Bauhinia s.l. is especially com- 2. Materials and methods plex. It has been the subject of a large number of taxonomic studies in which it has been recognized either as a single large genus comprising About 250 pollen samples (Table 1) were examined using light 300 to 350 species (e.g. Wunderlin et al., 1987), or as several distinct microscopy (LM), scanning electron microscopy (SEM) and transmis- genera (e.g. Lewis and Forest, 2005; Sinou et al., 2009). Recent molecular sion electron microscopy (TEM). The taxonomy follows that of Lewis phylogenetic studies (Sinou et al., 2009; Tu et al., 2013) are adding and Forest (2005) and Sinou et al. (2009). Pollen material was obtained support to the paraphyly of Bauhinia s.l. from specimens housed in the Herbarium of the Royal Botanic Gardens, The pollen of the Cercideae has long been known to be diverse and Kew (K); a list of all specimens studied is available upon request. variable. Until recently, it has been difficult to unravel the taxonomic Mature unopened buds from herbarium specimens were dissected significance of these diverse pollen structures due to the unresolved in a 1% solution of Libsorb wetting agent. Pollen was acetolysed species level taxonomy. With the recent publication of a molecular according to Erdtman (1960) and prepared for LM by mounting in glycerol jelly. Light micrographs were taken using a Leica DMLB micro- scope with an Axiocam digital camera. For SEM, acetolysed pollen ⁎ Corresponding author. Tel.: +44 20 8332 5363. E-mail addresses: [email protected] (H. Banks), [email protected] (F. Forest), exines in 95% ethanol were pipetted onto specimen stubs and allowed [email protected] (G. Lewis). to air dry. Specimens were sputter coated with platinum and examined

Please cite this article as: Banks, H., et al., Palynological contribution to the systematics and taxonomy of Bauhinia s.l. (Leguminosae: Cercideae), South African Journal of Botany (2013), http://dx.doi.org/10.1016/j.sajb.2013.07.028 2 laect hsatcea:Bns . ta. ayooia otiuint h ytmtc n aooyo ahnasl Lgmnse Cercideae (Leguminosae: s.l. Bauhinia of taxonomy and systematics (2013), the Botany to contribution of Palynological Journal al., African et South H., Banks, as: article this cite Please http://dx.doi.org/10.1016/j.sajb.2013.07.028 .Bnse l ot fia ora fBtn x 21)xxx (2013) xxx Botany of Journal African South / al. et Banks H.

Table 1 Table of pollen aperture, ornamentation and wall structure morphology in the Cercideae.

Group Apertures Ornamentation Wall structure Species included Figs.

Unspecialised type for Tricolporate, granular aperture membranes Microreticulate Foot layer, columellae and tectum present Figs. 1A, comparison B, C Cercis Tricolporate, granular aperture membranes Microreticulate Foot layer, columellae and tectum present C. canadensis, C. chinensis Adenolobus Tricolporate, granular aperture membranes Microreticulate Foot layer, columellae and tectum present A. garipensis, A. pechuellii Fig. 1B, C Griffonia Tricolporate, granular aperture membranes Microreticulate Foot layer, columellae and tectum present G. physocarpa Fig. 1A Gigasiphon macrosiphon Tricolporate Microreticulate Foot layer, columellae and tectum present Gigasiphon macrosiphon Fig. 1D Gigasiphon gossweileri Gemmate Supratectal gemmae Gigasiphon gossweileri Tylosema Tricolporate, annulus present around Microreticulate Thick foot layer, complex infratectum T. esculentum, T. fassoglensis –

endoaperture xxx Barklya Tricolporate Microreticulate, rugulate B. syringifolia Lysiphyllum Tricolporate Microreticulate, rugulate with variations Foot layer, columellae and tectum present L. cunninghamii, L. binata, between species, some have smoother L. hookeri, L. winitii areas around poles Schnella type 1 Tricolporate, granular aperture membrane Microperforate, psilate or finely rugulate Thick foot layer, thick tectum S. outimouta, S. hymenaeifolia, Fig. 1E and granular infratectum S. guianensis, S. angulosa, S. coronata, S. erythrantha, S. platycalyx, S. rutilans Schnella type 2 Tricolporate Gemmate Thick endexine, complex infratectum, S. microstachya, B. (S.) raddiana, S. Fig. 1F supratectal gemmae smilacina Lasiobema and Tricolporate, granular aperture membranes Microreticulate-rugulate, smoother Lasiobema pencilliloba, Phanera Asian Phanera type 1 areas around poles yunnanensis Lasiobema and Tricolporate, granular aperture membranes Microreticulate with larger lumina at Phanera vahlii, P. ornata Asian Phanera type 2 poles Lasiobema and Tripororate, finely granular aperture membranes Microperforate-psilate Foot layer, columellae and tectum present, Phanera bidentata,B.(Phanera) endertii, Fig. 1H, I Asian Phanera type 3 narrow infratectum P. foraminifera P. fulva, P. kockiana Lasiobema and Tricolporate, syncolporate Rugulate-verrucate, with larger verrucae Phanera glauca ssp. tenuiflora Fig. 1G Asian Phanera type 4 along aperture margins and over P. corymbosa aperture membranes B. damioshanensis P. touranensis ), B. (Phanera) clemensiorum Group

Apertures Ornamentation Wall structure Species included Figs.

laect hsatcea:Bns . ta. ayooia otiuint h ytmtc n aooyo ahnasl Lgmnse Cercideae (Leguminosae: s.l. Bauhinia of taxonomy and systematics (2013), the Botany to contribution of Palynological Journal al., African et South H., Banks, as: article this cite Please Lasiobema and Triporate Microperforate spinose-microspinose Phanera involucellata and P. bracteata Fig. 2A Asian Phanera type 5 Lasiobema and Tricolporate Spinose Bauhinia (Lasiobema?) harmsiana var. Asian Phanera type 6 harmsiana Piliostigma Triporate, operculate Microreticulate-spinose P. thonningii, P. malabarica Figs. 1J, 2B Brenierea Tricolporate Microreticulate-ﬁnely rugulate Thick foot layer B. insignis Bauhinia s.s. – Tricolporate, granular aperture membrane Microreticulate-microrugulate Foot layer, columellae and tectum present B. petersiana, B. bohniana Pseudobauhinia Bauhinia s.s. – Telestria type Tricolporate, granular aperture membrane Striate Infratectum columellate but with infrequent B. variegata 1 columellae present, supratectal striae Bauhinia s.s. – Telestria type Tricolporate, granular aperture membrane Microreticulate-microrugulate B. galpinii 2 Bauhinia s.s. – Tricolporate, granular aperture membrane Microperforate, perforate Foot layer, narrow infratectum and thick tectum present. B. phoenicia, B. potsii Fig. 1K Pseudophanera in B. pottsii, parasyncolporate in B. phoenicea or perforate-verrucate Calymate tetrahedral tetrads in B. phoenicea; common walls TETRADS between grains have greatly reduced ektexine which is perforated in places. Acalymate tetrahedral tetrads in http://dx.doi.org/10.1016/j.sajb.2013.07.028 B. pottsii. Bauhinia s.s. – Afrobauhinia Tricolporate, granular aperture membrane Striate A foot layer is present in the wall structure, columellae B. grandidieri, Fig. 2C

aresparse,thestriaearesupratectal B. hildebrandti, xxx (2013) xxx Botany of Journal African South / al. et Banks H. B. monandra, B. porosa Bauhinia s.s. – Alvesia Cryptoaperturate, four to six colpate Reticulate, gemmate or clavate B. taitensis, B. tomentosa Fig. 2F Bauhinia s.s. – Micralvesia No data No data No data Bauhinia s.s. – Pauletia 1 Colpate Gemmate or clavate Thick foot layer, and large supratectal gemmae or clavae B. pinheiroi, B. rufa Bauhinia s.s. – Bauhinia type Tricolporate Microreticulate, sparsely gemmate No foot layer. Thin tectum. B. pringlei 1 Large supratectal gemmae or clavae. Thick intine Bauhinia s.s. – Bauhinia type Tricolporate, with granular aperture membranes Striate Supratectal striae B. lunarioides, Figs. 2D, 2 B. macranthera, E B. ramosissima, B. jenningsii, B. subrotundifolia. B. dipetala Bauhinia s.s. – Pauletia 2Colpate,morethanthreeapertures, Microreticulate, gemmate-clavate Foot layer present, columellate infratectum, B. aculeata, B. bauhinioides, Figs. 2G, usually ﬁve or six supratectal gemmae or clavae. B. corniculata, B. pauletia, H B. pentrandra Bauhinia s.s. – Amaria Triporate (B. picta) or colpate/cryptoaperturate Microreticulate, spinose The infratectum is formed from three different sizes of B. picta, B. seminarioi Figs. 1L, (B. seminarioi) columellae, 2I the largest columellae form the spines which hold up, and project through, the reticulate tectum – xxx ), 3 4 H. Banks et al. / South African Journal of Botany xxx (2013) xxx–xxx

Fig. 1. A. Griffonia physocarpa, whole grain polar view SEM. Scale bar = 20 μm. B. Adenolobus pechuellii, SEM showing detail of aperture. Scale bar = 5 μm. C. Adenolobus pechuellii,TEM showing detail of wall structure. Scale bar = 1 μm. D. Gigasiphon macrosiphon, SEM of whole grain, equatorial view. Scale bar = 10 μm. E. Schnella coronata, TEM showing detail of wall structure; note granular infratectum. Scale bar = 1 μm. F. Bauhinia smilacina, TEM showing detail of wall structure and supratectal gemma. Scale bar = 1 μm. G. Bauhinia corymbosa, SEM showing syncolporate apertures. Scale bar = 10 μm. H. Bauhinia bidentata, SEM showing whole grain. Scale bar = 10 μm. I. Bauhinia endertii, SEM showing detail of aperture. Scale bar = 5 μm. J. Piliostigma thonningii, SEM showing whole grain, note porate aperture with operculum. Scale bar = 10 μm. K. Bauhinia phoenicea,SEMshowingpermanenttetrads. Scale bar = 25 μm. L. Bauhinia seminaroi, SEM showing a broken area of wall with columellae visible. Scale bar = 1 μm.

using a Hitachi S-2400 SEM at 18 kV, or a Hitachi FESEM S-4700 SEM structures onto the molecular phylogeny of Cercideae redrawn from at 2 kV. For TEM, acetolysed material was ﬁxed with a 2% solution of Sinou et al. (2009). osmium tetroxide (OsO4) in cacodylate buffer and pre-stained with 0.5% uranyl acetate, before embedding in Epon-araldite resin following the method of Skvarla (1966). The pollen was then thin-sectioned using 3.1. Overview of pollen types revealed in this study a Reichert Ultracut with a diamond knife, post-stained with uranyl acetate and lead citrate in an LKB Ultrostainer, and subsequently exam- Unspecialised pollen of Cercis, Adenolobus, Griffonia, Gigasiphon ined in a Hitachi H-300 TEM, Hitachi H-7650 TEM, or a Jeol JEM 1210 macrosiphon, Barklya, Brenieria, Lysiphyllum and some species of Bauhinia TEM at 80 kV. s.s. (Bauhinia petersiana, Bauhinia bohniana,andBauhinia galpinii)have Pollen samples have been databased and LM slides are available tricolporate, prolate to spheroidal, microreticulate or perforate-rugulate for consultation at the Jodrell Laboratory, Royal Botanic Gardens, Kew. pollen (Fig. 1A–D). In the Schnella (Wunderlin, 2010)cladethereare Palynological terminology follows Punt et al. (2007). two pollen types. In the ﬁrst type, pollen is small, tricolporate, and micro-rugulate, and the wall structure has a well developed granular 3. Results infratectum (Fig. 1E). This group includes Schnella outimouta, Schnella hymenaeifolia, Schnella guianensis, Schnella angulosa, Schnella oronate, Our results are presented in Table 1, which summarises the pollen Schnella erythrantha, Schnella platycalyx,andSchnella rutilans. The second morphology of specimens studied and facilitates the comparison of type has tricolporate pollen with supratectal gemmate ornamentation pollen structures. The accompanying images (Figs. 1A–2I) further (Fig. 1F) and includes Schnella microstachya, Schnella smilacina,and facilitate comparison. Fig. 3 shows the distribution of various pollen Bauhinia (Schnella) raddiana.

Fig. 2. A. Phanera bracteata SEM of whole grains showing porate apertures. Scale bar = 50 μm. B. Piliostigma thonningii SEM of whole grain showing porate apertures. Scale bar = 10 μm. C. Bauhinia hildebrandtii (Afrobauhinia group), SEM of whole grain showing striate surface ornamentation. Scale bar = 25 μm. D. Bauhinia dipetala (Bauhinia group), SEM of whole grain showing striate surface ornamentation with variation in the size of the individual striae. Scale bar = 10 μm. E. Bauhinia macranthera (Bauhinia group), whole grain showing striate surface ornamentation. Scale bar = 10 μm. F. Bauhinia tomentosa (Alvesia group), SEM close up of equatorial region showing colpi that are difﬁcult to distinguish because the ectoaperture is not visible (cryptoaperturate) (four to six colpi present per pollen grain). Scale bar = 5 μm. G. Bauhinia aculeata (Pauletia II group), SEM of whole grain showing four of seven apertures. Scale bar = 10 μm. H. Bauhinia bauhinioides (Pauletia II group, SEM of whole grain showing six apertures. Scale bar = 10 μm. I. Bauhinia picta (Amaria group), SEM close up of porate aperture. Scale bar = 5 μm.

Fig. 3. The distribution of pollen structures discussed in the text mapped onto the molecular phylogenetic tree of tribe Cercideae (redrawn from Sinou et al., 2009).

From the Phanera/Lasiobema clade, only six species were sampled apertures in the Pauletia IandPauletia II groups, and triporate or in the molecular phylogeny of Sinou et al. (2009). Our pollen analysis cryptoaperturate in the Amaria group. shows six very different pollen types in the species so far sampled from this group. Of these, the pororate pollen present in Phanera 4.2. Surface ornamentation and wall structure bidentata (Fig. 1H), Bauhinia (Phanera) endertii (Fig. 1I), (and also Phanera foraminifera, Phanera fulva,andPhanera kockiana), is not The presence of verrucate, gemmate, spinose, striate and clavate present anywhere else in the Leguminosae (Graham and Barker, 1981; ornamentation types is common in Bauhinia s.l. A reticulate exine Banks and Klitgaard, 2000; Banks et al., 2003). The Phanera corymbosa supporting supratectal ornamentation has been recorded by authors type, with syncolporate apertures and supratectal verrucae (Fig. 1G), who have studied the pollen grains of Bauhinia s.l. taxa (Melhem is similar in all five taxa studied so far (Phanera glauca ssp. tenuiflora, and Salgado-Labouriau, 1963; Schmitz, 1973; Ferguson, 1987; Gamerro Phanera corymbosa, Bauhinia damioshanensis, Phanera touranensis,and and Fortunato, 2001). These types of surface ornamentation may Bauhinia (Phanera) clemensiorum), and supports research currently be useful for taxonomy at the species level, but the same patterns being carried out by B. Mackinder and colleagues (Personal Communi- appear repeatedly in Bauhinia s.s., Phanera, Schnella and Lasiobema, cation), which places these taxa into a new, as yet undescribed, genus. and throughout caesalpinioid legumes (Graham and Barker, 1981; There are two spinose pollen types in this clade, one with porate pollen Banks and Klitgaard, 2000; Banks et al., 2003). According to Ferguson (Phanera oronate and Phanera bracteata), and one with colporate pollen (1987), the variation and specialisation of features of the pollen [Bauhinia (Lasiobema) harmsiana var. Harmsiana]. Of the two remaining exine of Bauhinia s.l., together with the aperture patterns, place the pollen types, one is tricolporate-rugulate with smoother polar areas genus as one of the most specialised within subfamily Caesalpinioideae. (Lasiobema pencilliloba and Phanera yunnanensis)andtheotheris However, most phylogenetic studies of the Leguminosae support tricolporate-reticulate (Phanera vahlii and Phanera orona). More exten- tribe Cercideae as the first diverging clade within the family sive sampling for molecular phylogenetic analyses is needed in this very (e.g. Wojciechowski et al., 2004; Bruneau et al., 2008; Sinou interesting group. et al., 2009). The generalised pollen types of the first branching In the Bauhinia s.s. clade, there are unspecialised pollen types in genera in the Cercideae clade may be regarded as a plesiomorphic B. petersiana, B. bohniana,andB. galpinii. In section Pseudobauhinia,pol- pollen type for legumes, while other specialised features of the exine len tetrads occur in Bauhinina phoenicea and Bauhinia pottsii. Striate, found in Lasiobema, Phanera, Schnella and Bauhinia s.s. could be tricolporate pollen occurs in one of the two Telestria pollen types in regarded as more specialised evolutionary acquisitions. Wall and aper- Bauhinia variegata, Bauhinia grandidieri, Bauhinia hildebrandtii, Bauhinia ture structure are developed earlier during the ontogeny (Blackmore monandra and Bauhinia porosa in section Afrobauhinia,andoneofthe and Crane, 1998), and this is possibly why they appear to be more twopollengroupsinsectionBauhinia comprising Bauhinia lunarioides, fixed developmentally than surface ornamentation, which is the last Bauhinia macranthera, Bauhinia ramosissima, Bauhinia jenningsii, structure to be laid down during development. Because of this, it is Bauhinia subrotundifolia and Bauhinia dipetala. Gemmate tricolporate possible that wall and aperture structure are less open to rapid change, pollen occurs in one of the two pollen groups in section Bauhinia and are therefore more indicative of phylogenetic relationships, than (Bauhinia pringlei). Densely gemmate, four to six cryptoaperturate, surface ornamentation. colpate pollen occurs in section Alvesia,comprisingBauhinia taitensis Some species of Bauhinia have large flowers with white petals, and Bauhinia tomentosa. Gemmate, six to seven colpate pollen, occurs nocturnal anthesis, and nectar produced inside a cylindrical-tubular hy- in the Pauletia IandPauletia II groups, comprising Bauhinia pinheiroi, panthium (Queiroz, 2009). These features match the criteria defined Bauhinia rufa, Bauhinia aculeata, Bauhinia bauhinioides, Bauhinia by Faegri and van der Pijl (1971) for chiropterophily (bat pollination). corniculata, Bauhinia pauletia,andBauhinia pentandra. Ornamenta- Arroyo (1981) has reported that species of Bauhinia with such features tion of spines formed from columellae occurs in the Amaria group, are largely pollinated by bats. This has been subsequently confirmed by which has apertures that are either cryptoaperturate (Bauhinia other pollination studies (Heithaus et al., 1982; Muchhala and Jarrín, seminarioi)orporate(Bauhinia picta). 2005). Species of Phanera have much smaller flowers with matutinal anthesis and a wider, campanulate hypanthium (Queiroz, 2009), and are probably pollinated by bees. Large supratectal processes 4. Discussion in caesalpinioid legumes have been reported for the Amazonian genera Dicymbe Spruce ex Benth., Eperua Aubl., and Paloue Aubl. (tribe 4.1. Apertures Detarieae; Graham and Barker, 1981; Banks and Rico, 1999)plus Paloveopsis, Elizabetha, Browneopsis and Ecuadendron (Banks and Variation in the number of apertures in different species of Bauhinia Klitgaard, 2000). Species of these genera are largely pollinated by bats and Phanera was first recorded by Vishnu and Sharma (1962),who (Arroyo, 1981), which may suggest an association between this kind described pollen types in Indian Bauhinia s.l. species ranging from of ornamentation and adaptation to bat pollination. Some other types inaperturate to 3-aperturate. Larsen (1975) described pollen grains of supratectal ornamentation, such as that present in Schnella,maybe of Thai species ranging from inaperturate to 3–5-aperturate, and associated with butterfly pollination. Ferguson and Pearce (1986) found 3–7-zonoaperturate pollen grains The wall structure of legume pollen has been documented as an in neotropical species. Heteromorphism in aperture number has also important character in subfamilies Caesalpinioideae (Ferguson, 1987; been recorded in Bauhinia s.l. species by Schmitz (1973) and Gamerro Banks and Klitgaard, 2000) and Mimosoideae (Guinet, 1981) where it and Fortunato (2001).InBauhinia s.s. (sensu Wunderlin et al., 1987), is also suggested to be associated with different aperture structures the species possess 3–7-colpate, colporoidate, or 5–7-porate pollen (colpori and pores). The importance of understanding the wall structure grains. According to Wunderlin et al. (1987), pollen grains are 3–7- in relation to pollen biology has previously been demonstrated in colpate with supratectal elements in the series Cansenia and subfamily Papilionoideae (Ferguson and Skvarla, 1981, 1983) and has Perlebia (belonging to Bauhinia sect. Pauletia). In Bauhinia cheilantha been discussed in subfamily Caesalpinioideae (Banks and Klitgaard, and Bauhinia subclavata, the pollen grains are porate. This study 2000). shows aperture variation (porate, pororate, and syncolporate) in three pollen types of the Asian Phanera/Lasiobema clade, plus porate pollen 4.3. Structures of systematic importance in Piliostigma,andfive Bauhinia s.s. groups, parasyncolorate in the Pseudophanera group, cryptoaperturate and colpate with more than Pollen grains of the first branching lineages in the Cercideae are three apertures in the Alvesia group, colpate with more than three unspecialised; they are isopolar, spheroidal to prolate, tectate, tricolporate

Please cite this article as: Banks, H., et al., Palynological contribution to the systematics and taxonomy of Bauhinia s.l. (Leguminosae: Cercideae), South African Journal of Botany (2013), http://dx.doi.org/10.1016/j.sajb.2013.07.028 H. Banks et al. / South African Journal of Botany xxx (2013) xxx–xxx 7 and released in monads. Surface ornamentation may be micro-reticulate 4.3.3. Repeatedly occurring pollen structures (Fig. 3) or perforate, and psilate to oronate. Aperture membranes are granular Supratectal ornamentation, structures such as gemmae, verrucae, to coarsely granular. Taxa that have an unspecialised pollen class spines and striae, occur in many species within Cercideae, as well as include Cercis, Adenolobus, Griffonia, G. macrosiphon, Tylosema, Barklya, throughout the Caesalpinioideae. Lysiphyllum, B. petersiana,andB. bohniana (Fig. 1A–D). More specialised Surface ornamentation types may be useful for taxonomy at the types of pollen grains are found in Schnella, Lasiobema and Phanera, species level, but the same patterns of surface ornamentation appear Piliostigma and most of Bauhinia s.s. (Fig. 1E–L). repeatedly in Bauhinia, Phanera and Lasiobema, and throughout As a result of this study, we are able to discuss pollen structures that caesalpinioid legumes (Graham and Barker, 1981; Banks and Klitgaard, are of systematic and taxonomic importance both within the Cercideae 2000; Banks et al., 2003). While useful for taxonomy at the species as a clade, and in Caesalpinioideae, building on previous studies of this level, surface ornamentation is discounted as a potential diagnostic subfamily (Graham and Barker, 1981; Ferguson, 1987; Banks and character at higher taxonomic levels, and is thought to be associated Klitgaard, 2000). In tribe Cercideae there are distinct pollen structures with pollination syndromes. that occur nowhere else in subfamily Caesalpinioideae, and distinct pollen structures that identify and define groups of taxa. There are also pollen types that occur repeatedly in the Caesalpinioideae, as well 4.4. Pollen, systematics and taxonomy as pollen structures that are homoplastic within the subfamily. Molecular analyses show that genus Bauhinia s.l. is not monophyletic, fi 4.3.1. Distinct pollen structures, diagnostic for groups of related due to the nested position of the monospeci cgenusBrenierea within it. species (Fig. 3) The pollen morphology of Brenierea is very similar to pollen of Cercis, Six specialised pollen structures have been identified as occurring Adenolobus, Griffonia, Gigasiphon, Barklya, Lysiphyllum and Bauhinia s.s. only in small groups of related species: species (B. petersiana, B. bohniana,andB. galpinii). The pollen morphology found in Schnella, Lasiobema, Phanera, Piliostigma and most species 4.3.1.1 Within Cercideae, a granular infratectum occurs only in the of Bauhinia s.s. shows a high level of specialisation, and has pollen wall structure of some species of Schnella (Table 1, Fig. 1E). types that are quite distinct if supratectal surface ornamentation is The pollen grains are otherwise small and unspecialised, in discounted, as discussed above. This supports recent suggestions by contrast to a second type of gemmate pollen in Schnella that has Lewis and Forest (2005) and Sinou et al. (2009) based on molecular anal- a different type of wall structure (Fig. 1F). yses, that Bauhinia s.l. is not monophyletic. Earlier taxonomic and palyno- 4.3.1.2 Within Cercideae, syncolporate apertures occur only in a group of logical studies (e.g., de Wit 1956; Wunderlin 1979; Wunderlin et al., five related species in Lasiobema/Phanera (Table 1, Fig. 1G). The 1981, 1987; Schmitz, 1977; Zhang, 1995), also demonstrated that verrucate ornamentation covering the pollen surface and aperture Bauhinia s.l. has distinct groups of taxa within it. The pollen of Piliostigma membranes is also distinctive. These species have been identified is also very distinct, having pores with spiny opercula and spinose as belonging to an undescribed new genus (Mackinder et al., ornamentation. The pollen of Gigasiphon gossweileri is notably distinct 2013). from that of G. macrosiphon, suggesting that the species within that 4.3.1.3 Pororate apertures are present only in four Lasiobema/Phanera genus are not a homogeneous assemblage. species (Table 1, Fig. 1H,I).Thisisanaperturetypenotseen in any other caesalpinioid legume. 4.3.1.4 A distinctive spiny operculum covers the pores of Piliostigma References

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