Molecular phylogenetics of Paphiopedilum (Cypripedioideae; Orchidaceae) based on nuclear ribosomal ITS and plastid sequences ARAYA CHOCHAI 1,2 *, ILIA J. LEITCH FLS 1 , MARTIN J. INGROUILLE 2 and MICHAEL F. FAY FLS 1 1 Jodrell Laboratory, Royal Botanic Gardens, Kew, Richmond, Surrey TW9 3DS, UK 2 Department of Biological Sciences, Birkbeck, University of London, Malet Street, London WC1E 7HX, UK Received 24 February 2012; revised 30 May 2012; accepted for publication 24 June 2012 Phylogenetic relationships in the genus Paphiopedilum were studied using nuclear ribosomal internal transcribed spacer (ITS) and plastid sequence data. The results confirm that the genus Paphiopedilum is monophyletic, and the division of the genus into three subgenera Parvisepalum, Brachypetalum and Paphiopedilum is well supported. Four sections of subgenus Paphiopedilum (Pardalopetalum, Cochlopetalum, Paphiopedilum and Barbata) are recovered as in a recent infrageneric treatment, with strong support. Section Coryopedilum is also recovered, with low bootstrap but high posterior probability values for support of monophyly. Relationships in section Barbata remain unresolved, and short branch lengths and the narrow geographical distribution of many species in the section suggest that it possibly underwent rapid radiation. Mapping chromosome and genome size data (including some new genome size measurements) onto the phylogenetic framework shows that there is no clear trend in increase in chromosome number in the genus. However, the diploid chromosome number of 2n = 26 in subgenera Parvisepalum and Brachypetalum suggests that this is the ancestral condition, and higher chromosome numbers in sections Cochlopetalum and Barbata suggest that centric fission has possibly occurred in parallel in these sections. The trend for genome size evolution is also unclear, although species in section Barbata have larger genome sizes than those in other sections. © 2012 The Linnean Society of London, Botanical Journal of the Linnean Society, 2012, 170, 176–196. ADDITIONAL KEYWORDS: centric fission – chromosome number – evolution – genome size – infrageneric classification. INTRODUCTION The genus Paphiopedilum Pfitzer comprises c. 72 species (Averyanov et al., 2003), distributed from India and southern China through south-east Asia and the Malesian islands to the Solomon Islands (Cribb, 1998). Most species are terrestrial, but some are epiphytic or lithophytic (Cribb, 1998). This genus is the largest of the five genera of slipper orchids in subfamily Cypripedioideae (Orchidaceae). The other genera are Phragmipedium Rolfe, Selenipedium Rchb.f., Cypripedium L. and Mexipedium V.A.Albert & M.W.Chase. Floral characteristics of the slipper orchids are a slipper-shaped lip, two fertile stamens, a shield-like staminode and united lateral sepals or a synsepal (Cox et al., 1997). There is no unique mor- phological character to distinguish the slipper orchid genera from each other, but they can be distinguished by a combination of morphological characters, includ- ing leaf type, number of locules, type of placentation and geographical distribution (Cox et al., 1997). The characteristics of Paphiopedilum are conduplicate leaves, imbricate sepal aestivation and a unilocular ovary with parietal placentation. Paphiopedilum can be distinguished from the Northern Hemisphere Cypripedium and the tropical American Selenipedium by those genera having plicate leaves and perfor- ate sepal aestivation. In addition, Selenipedium is distinguished by a trilocular ovary with axile pla- centation. Among the conduplicate leaved genera, *Corresponding author. E-mail: a.chochai@kew.org Botanical Journal of the Linnean Society, 2012, 170, 176–196. With 5 figures © 2012 The Linnean Society of London, Botanical Journal of the Linnean Society, 2012, 170, 176–196 176 Downloaded from https://academic.oup.com/botlinnean/article/170/2/176/2416252 by guest on 05 December 2023