Developmental and Structural Section
Prenner, Gerhard , Rudall, Paula, J. .
Morphology and evolution of the cyathium in Euphorbieae (Euphorbiaceae-Malpighiales).
AN outstanding morphological feature of Euphorbieae is its inflorescence, termed a cyathium, which resembles a bisexual flower and contrasts strongly in organization with inflorescences of the vast majority of other Euphorbiaceae and other angiosperms. The cyathium consists of a cuplike structure of fused bracts, often with distinct extrafloral nectar glands and showy petaloid appendages; within the cup, a single terminal female flower is surrounded by four or five male structures which are normally interpreted as inflorescences. Perianth parts are absent, at least in Euphorbiinae, in which flowers consist solely of a stalked gynoecium (in female flowers) or a single stamen (in male flowers), though a perianth is present in the related subtribe Anthosteminae and in female flowers of subtribe Neoguillauminiinae. In Euphorbiinae, constrictions below the filament or gynoecium have been regarded as clues to the position of a suppressed perianth. The uniqueness of the cyathium makes it a good subject for posing homology questions about the flower–inflorescence boundary. We present detailed ontogenetic studies of cyathia from representatives of all subtribes of Euphorbieae: Euphorbiinae (Euphorbia, Synadenium, Monadenium, Pedilanthus), Anthosteminae (Dichostemma glaucescens), and Neoguillauminiinae (Neoguillauminia cleopatra), together with comparative data on flowers and inflorescences of selected representatives of other Euphorbiaceae. Based on these studies we discuss the evidence for a pseudanthial nature of the cyathium and present hypotheses on the origin and evolution of the cyathium in Euphorbiaceae. We also discuss the morphological evidence for recent molecular results which indicate that Euphorbia is paraphyletic with respect to other currently recognized genera (i.e., Chamaesyce, Cubanthus, Endadenium, Monadenium, Pedilanthus and Synadenium) nested within it.
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1 - Royal Botanic Gardens, Kew, Jodrell Laboratory, Richmond, Surrey, TW9 3AB, United Kindom,
2 - Royal Botanic Gardens, Kew, Jodrell Laboratory, Richmond, Surrey, TW9 3AB, United Kingdom,
Presentation Type: Oral Paper:Papers for Sections
Location: 303/Bell Memorial Union
Date: Monday, July 31st, 2006
Time: 9:00 AM