Damerval Catherine, Nadot Sophie
CNRS UMR Génétique Végétale, INRA, AgroParisTech, Université Paris-Sud, Gif-sur-Yvette, F-91190, France.
Ann Bot. 2007 Sep;100(3):631-40. doi: 10.1093/aob/mcm041. Epub 2007 Apr 11.
Floral symmetry presents two main states in angiosperms, namely polysymmetry and monosymmetry. Monosymmetry is thought to have evolved several times independently from polysymmetry, possibly in co-adaptation with specialized pollinators. Monosymmetry commonly refers to the perianth, even though associated androecium modifications have been reported. The evolution of perianth symmetry is examined with respect to traits of flower architecture in the Ranunculales, the sister group to all other eudicots, which present a large diversity of floral forms.
Characters considered were perianth merism, calyx, corolla and androecium symmetry, number of stamens and spurs. Character evolution was optimized on a composite phylogenetic tree of Ranunculales using maximum parsimony.
The ancestral state for merism could not be inferred because the basalmost Eupteleaceae lack a perianth and have a variable number of stamens. The Papaveraceae are dimerous, and the five other families share a common trimerous ancestor. Shifts from trimery to dimery (or reverse) are observed. Pentamery evolved in Ranunculaceae. Ranunculales except Eupteleaceae, present a polysymmetric ancestral state. Monosymmetry evolved once within Papaveraceae, Ranunculaceae and Menispermaceae (female flowers only). Oligandry is the ancestral state for all Ranunculales, and polyandry evolved several times independently, in Papaveraceae, Menispermaceae, Berberidaceae and Ranunculaceae, with two reversions to oligandry in the latter. The ancestral state for androecium symmetry is ambiguous for the Ranunculales, while polysymmetry evolved immediately after the divergence of Eupteleaceae. A disymmetric androecium evolved in Papaveraceae. The ancestral state for spurs is none. Multiple spurs evolved in Papaveraceae, Berberidaceae and Ranunculaceae, and single spurs occur in Papaveraceae and Ranunculaceae.
The evolution of symmetry appears disconnected from changes in merism and stamen number, although monosymmetry never evolved in the context of an open ground plan. In bisexual species, monosymmetry evolved coincidently with single spurs, allowing us to propose an evolutionary scenario for Papaveraceae.
花对称性在被子植物中呈现出两种主要状态，即多对称性和单对称性。单对称性被认为是从多对称性独立进化而来的，可能是与特化传粉者共同适应的结果。单对称性通常指的是花被，尽管也有相关雄蕊变化的报道。鉴于毛茛目是所有其他真双子叶植物的姐妹群，且具有多种花形态，本文通过花结构特征研究了花被对称性的进化。
研究的特征包括花被轮数、花萼、花冠和雄蕊对称性、雄蕊数量和距。利用最大简约法在毛茛目的复合系统发育树上对特征进化进行优化。
由于最基部的领春木科没有花被且雄蕊数量可变，无法推断轮数的祖先状态。罂粟科是两轮的，其他五个科有一个共同的三轮祖先。观察到从三轮向两轮（或相反）的转变。毛茛科进化出了五轮。除领春木科外，毛茛目呈现多对称的祖先状态。单对称性在罂粟科、毛茛科和防己科（仅雌花）中各独立进化了一次。少雄蕊是所有毛茛目的祖先状态，多雄蕊在罂粟科、防己科、小檗科和毛茛科中多次独立进化，毛茛科中有两次逆转回少雄蕊状态。毛茛目雄蕊对称性的祖先状态不明确，而在领春木科分化后立即进化出了多对称性。罂粟科进化出了不对称雄蕊。距的祖先状态是无。多距在罂粟科、小檗科和毛茛科中进化出来，单距出现在罂粟科和毛茛科中。
对称性的进化似乎与轮数和雄蕊数量的变化无关，尽管单对称性从未在开放的基本结构背景下进化。在两性花物种中，单对称性与单距同时进化，这使我们能够为罂粟科提出一个进化假说。
