Evolution of pollen, stigmas and ovule numbers at the caesalpinioid–mimosoid interface (Fabaceae) HANNAH BANKS*, ILARI HIMANEN and GWILYM P. LEWIS Royal Botanic Gardens, Kew, Richmond, Surrey, TW9 3AB, UK Received 5 August 2009; accepted for publication 22 October 2009 In this study we examine the pollen, stigmas and ovaries from 62 collections of herbarium material representing 16 genera, using light and scanning electron microscopy. The caesalpinioid Dimorphandra group (Burkea, Dimorphan- dra, Erythrophleum, Mora, Pachyelasma, Stachyothyrsus and Sympetalandra) pollen grains are small, tricolporate monads, with perforate or psilate ornamentation. Dinizia, Pentaclethra and Aubrevillea have morphological characters that have suggested either a mimosoid or caesalpinioid placement. Dinizia pollen is in permanent tetrads with clavate ornamentation. Pentaclethra pollen grains are monads, two species have tricolporate pollen and the third is porate. Aubrevillea has tricolporate, finely reticulate monads. All ten genera have variable, non-predictable stigma type and ovule number. The mimosoid Adenanthera group (Adenanthera, Tetrapleura, Amblygonocarpus, Pseudoprosopis, Calpocalyx and Xylia) pollen grains are in 8- to 16-grain polyads. In all Adenanthera group species, the stigmatic cavity is only large enough to accommodate one polyad. In addition, the number of ovules present matches the number of pollen units in one polyad. Polyads have porate, operculate apertures that differ in layout, aperture morphology and development when compared with caesalpinioid and other eudicot pollen. © 2010 The Linnean Society of London, Botanical Journal of the Linnean Society, 2010, 162, 594–615. ADDITIONAL KEYWORDS: apertures – Caesalpinioideae – Leguminosae – Mimosoideae – monad – phylogeny – pollen development – polyad – reproductive syndrome. INTRODUCTION In Fabaceae, at the caesalpinioid–mimosoid boundary, relationships that include subfamily Mimosoideae and most Cassieae and Caesalpinieae subgroups are not fully resolved in the molecular phylogenetic analyses published to date (Bruneau et al., 2008). Phylogenetic studies so far indicate that some members of the Dimorphandra group (based on Dimorphandra Schott) of Caesalpinieae (e.g. Pachyelasma Harms, Eryth- rophleum Afzel. ex G.Don; Bruneau et al., 2008) com- prise the sister group to Mimosoideae, although relationships of lineages near the ‘base’ of the mimosoid clade are still poorly resolved and the Dimor- phandra group resolves into two clades in the molecu- lar phylogeny of Bruneau et al. (2008). Pollen is of great interest in this group, as it is mostly released in monads (or rarely tetrads, Ferguson & Banks, 1994) in caesalpinioids (Graham & Barker, 1981; Banks & Gasson, 2000; Banks & Klitgaard, 2000; Banks et al., 2003), whereas mostly polyads are found in mimosoid taxa (Guinet, 1981; Guinet & Ferguson, 1989). This study was carried out to investigate the pollen, stigmas and number of ovules per ovary of taxa in the Dimor- phandra group and first branching members of Mimosoideae, both to provide characters for phyloge- netic analyses and to investigate the putative evolu- tion of compound pollen from monads. MATERIAL AND METHODS Sixty-two samples from 42 collections of the 99 species in 16 genera (Table 1) were examined using light microscopy (LM) and scanning electron micros- copy (SEM). The taxonomy used is that of Lewis (2005) based on the earlier studies of Polhill & Vidal (1981) and Polhill (1994). Although there is a more *Corresponding author. E-mail: h.banks@rbgkew.org.uk GPL and HB usually publish under the family name Legumi- nosae, but are here following journal style in following APG III (2009) family names. Botanical Journal of the Linnean Society, 2010, 162, 594–615. With 39 figures © 2010 The Linnean Society of London, Botanical Journal of the Linnean Society, 2010, 162, 594–615 594 Downloaded from https://academic.oup.com/botlinnean/article-abstract/162/4/594/2418470 by guest on 31 May 2020