Hyper-epigyny is the ultimate constraint on orchid floral morphology and an ideal model for testing the Extended Synthesis - Royal Botanic Gardens, Kew research repository
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Book chapter

Hyper-epigyny is the ultimate constraint on orchid floral morphology and an ideal model for testing the Extended Synthesis

2019

Abstract

The developmental morphology and genetics of the orchid flower is described in order to explore the evolutionary ‘no man’s land’ that separates the Extended Synthesis from the Modern Synthesis. The gynostemium, ubiquitous among orchids and developed through congenital fusion (and dorsal suppression) of fertile reproductive organs, is an unbreakable evolutionary constraint of high burden. We agree with Mondragón-Palomino and Theissen that the fundamentally tripartite bauplan of six tepals of three morphologies constitutes a remarkably robust ‘super-organ’ but we would include the gynostemium in the super-organ concept. Within the fundamental constraint of this super-organ, intersecting clines of expression overlain by extensive pleiotropy are hypothesised to cause sufficient mosaicism and heterochrony to permit the evolution of vast numbers of trivially distinct species. We cannot yet estimate the contribution to evolvability of natural selection – directly through adaptation and indirectly through exaptation – relative to the non-aptations that must by definition reflect the many other causes of evolution.

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