RESEARCH PAPER Floral diversity and pollination strategies of three rheophytic Schismatoglottideae (Araceae) S. L. Low 1 , S. Y. Wong 1 , I. H. Ooi 1 , M. Hesse 2 , Y. St€ adler 2 , J. Sch € onenberger 2 & P. C. Boyce 3 1 Department of Plant Science and Environmental Ecology, Faculty of Resource Science and Technology, Universiti Malaysia Sarawak, Sarawak, Malaysia 2 Department of Structural and Functional Botany, University of Vienna, Vienna, Austria 3 Institute of Biodiversity and Environmental Conservation, Universiti Malaysia Sarawak, Sarawak, Malaysia Keywords Aridarum nicolsonii; Colocasiomyia; flowering mechanism; Phymatarum borneense; Schottarum sarikeense. Correspondence S. Y. Wong, Department of Plant Science and Environmental Ecology, Faculty of Resource Science and Technology, Universiti Malaysia Sarawak, 94300 Sarawak, Malaysia. E-mail: sywong@frst.unimas.my Editor N. Vereecken Received: 11 December 2014; Accepted: 12 February 2015 doi:10.1111/plb.12320 ABSTRACT Homoplastic evolution of ‘unique’ morphological characteristics in the Schismat- oglottideae – many previously used to define genera – prompted this study to compare morphology and function in connection with pollination biology for Aridarum ni- colsonii, Phymatarum borneense and Schottarum sarikeense. Aridarum nicolsonii and P. borneense extrude pollen through a pair of horned thecae while S. sarikeense sheds pollen through a pair of pores on the thecae. Floral traits of spathe constriction, pres- ence and movement of sterile structures on the spadix, the comparable role of horned thecae and thecae pores, the presence of stamen-associated calcium oxalate packages, and the timing of odour emission are discussed in the context of their roles in pollina- tor management. Pollinators for all investigated species were determined to be species of Colocasiomyia (Diptera: Drosophilidae). INTRODUCTION Homoplastic character evolution is increasingly being detected within angiosperm clades (Givnish et al. 1999; Scharaschkin & Doyle 2006; Garc  ıa et al. 2009; among others). Saether (1977) noted homoplasy within closely related clades as ‘underlying synapomorphies’ and described it as ‘canalized evolutionary potential repeatedly producing the same apomorphic condi- tions.’ On Borneo, rapid species diversification in tribe Schismat- oglottideae has been shown to involve homoplastic evolution within the smaller almost exclusively rheophytic genera (Wong et al. 2010; Wong 2013). Among homoplastic characters inves- tigated, horned thecae are of particular interest not only because they are a taxonomically localised characteristic in the aroids, but also because horned thecae are used for generic delimitation, and ‘pre-cladistics’ delimitated ‘related taxa’. Within Araceae, horned thecae are confined to two related tribes: Cryptocoryneae (Cryptocoryne Fisch. ex Wydler and Lagenandra Dalzell) and Schismatoglottideae (Aridarum M.Hotta, Bucephalandra Schott, Phymatarum M.Hotta and Schottariella P.C.Boyce & S.Y.Wong). The prevalence of this particular homoplastic trait in these four genera of Schismat- oglottideae prompted further investigation, along with attempts to understand the biological processes these mecha- nisms favour. Investigation of the flowering mechanisms and pollination strategies in Schismatoglottideae is so far limited to a few recent studies (Ulrich et al. 2012; Wong & Boyce 2013; Low et al. 2014). Boyce & Wong (2013) and Low et al. (2014) reported the pollinators for several Aridarum and Schottarum P.C.Boyce & S.Y.Wong species investigated were various Colocasiomyia de Meijere (Diptera: Drosophilidae), although they noted numer- ous incidental observations of inflorescence visitation by Sphaeridiinae and Staphylinidae (Coleoptera) to Aridarum (J. Bogner, personal communication; P. C. Boyce, personal observation; K. Nakamoto, personal communication) and Chrysomelidae (Coleoptera) to Bucephalandra, Ooia S.Y.Wong & P.C.Boyce and Schismatoglottis Zoll. & Moritzi (P. C. Boyce, personal observation; I. H. Ooi, personal observation). Chry- somelids are highly predatory and usually cause extensive physical damage to parts of the spadix, notably the appendix (Low et al. 2014). Several mechanisms have been observed that seem to provide protection for the inflorescence during anthe- sis. Among microstructures in the taxa under investigation, extracellular calcium oxalate crystals have a biotic role in inhib- iting herbivory (Franceschi & Horner 1980), but this is not nec- essarily true for all species investigated (Cot  e & Gibernau 2012) or in enhancing pollination (D’Arcy et al. 1996). The abundance and structural diversity of calcium oxalate crystal types in the Araceae have been investigated sporadi- cally in taxa across the family. Most of the investigations, however, have focused on the presence of crystals in vegeta- tive tissues (Keating 2004). D’Arcy et al. (1996) reported the presence of calcium oxalate crystals mixed with pollen in some Anthurium Schott, Calla L. and Zantedeschia Spreng. Studies have also revealed that extracellular calcium oxalate crystals are visible on the surface of the apical portion of Plant Biology © 2015 German Botanical Society and The Royal Botanical Society of the Netherlands 1 Plant Biology ISSN 1435-8603