Ronse De Craene Louis, Bull-Hereñu Kester
Royal Botanic Garden Edinburgh, Edinburgh, UK
Departamento de Ecología, Pontificia Universidad Católica de Chile, Santiago, Chile, Escuela de Pedagogía en Biología y Ciencias, Universidad Central de Chile and Fundación Flores, Ministro Carvajal 30, Santiago, Chile.
Ann Bot. 2016 Apr;117(5):709-24. doi: 10.1093/aob/mcw017. Epub 2016 Mar 24.
Obdiplostemony has long been a controversial condition as it diverges from diplostemony found among most core eudicot orders by the more external insertion of the alternisepalous stamens. In this paper we review the definition and occurrence of obdiplostemony, and analyse how the condition has impacted on floral diversification and species evolution.
Obdiplostemony represents an amalgamation of at least five different floral developmental pathways, all of them leading to the external positioning of the alternisepalous stamen whorl within a two-whorled androecium. In secondary obdiplostemony the antesepalous stamens arise before the alternisepalous stamens. The position of alternisepalous stamens at maturity is more external due to subtle shifts of stamens linked to a weakening of the alternisepalous sector including stamen and petal (type I), alternisepalous stamens arising de facto externally of antesepalous stamens (type II) or alternisepalous stamens shifting outside due to the sterilization of antesepalous stamens (type III: Sapotaceae). In primary obdiplostemony the alternisepalous stamens arise before the antesepalous stamens and are more externally from initiation. The antesepalous stamen whorl is staminodial and shows a tendency for loss (type I), or the petals are missing and the alternisepalous stamens effectively occupy their space (type II). Although obdiplostemony is often related to an isomerous gynoecium, this is not essential. Phylogenetically, both secondary and primary obdiplostemony can be seen as transitional stages from diplostemony to either haplostemony or obhaplostemony. Obdiplostemony is the consequence of shifts in the balance between the two stamen whorls, affecting either the alternisepalous stamens together with the petals, or the antesepalous stamens.
We advocate a broad definition of obdiplostemony, to include androecia with incomplete whorls, staminodial whorls, anisomerous gynoecia and an absence of petals. As such, the taxonomic significance of obdiplostemony is transient, although it is a clear illustration of how developmental flexibility is responsible for highly different floral morphs.
长期以来，异层雄蕊现象一直存在争议，因为在大多数核心真双子叶植物目中普遍存在的双轮雄蕊现象中，异层雄蕊的插入位置更靠外。在本文中，我们回顾了异层雄蕊现象的定义和出现情况，并分析了这种现象如何影响花的多样化和物种进化。
异层雄蕊现象代表了至少五种不同花发育途径的融合，所有这些途径都会导致两轮雄蕊中与花瓣互生的雄蕊轮处于外部位置。在次生异层雄蕊现象中，与花瓣对生的雄蕊先于与花瓣互生的雄蕊出现。成熟时，与花瓣互生的雄蕊位置更靠外，这是由于雄蕊的细微移动导致与花瓣互生雄蕊部分（包括雄蕊和花瓣）变弱（I型），与花瓣互生的雄蕊实际上起源于与花瓣对生雄蕊的外部（II型），或者是由于与花瓣对生雄蕊不育导致与花瓣互生的雄蕊向外移动（III型：山榄科）。在初生异层雄蕊现象中，与花瓣互生的雄蕊先于与花瓣对生的雄蕊出现，并且从开始就更靠外。与花瓣对生的雄蕊轮退化为雄蕊状，并呈现退化趋势（I型），或者花瓣缺失，与花瓣互生的雄蕊实际上占据了它们的位置（II型）。尽管异层雄蕊现象通常与同数雌蕊有关，但这并非必要条件。从系统发育角度看，次生和初生异层雄蕊现象都可视为从双轮雄蕊现象到单轮雄蕊现象或异单轮雄蕊现象的过渡阶段。异层雄蕊现象是两轮雄蕊之间平衡变化的结果，这种变化影响了与花瓣互生的雄蕊连同花瓣，或者与花瓣对生的雄蕊。
我们主张对异层雄蕊现象进行宽泛定义，包括雄蕊轮不完整、雄蕊状轮、不同数雌蕊以及无花瓣的雄蕊群。因此，异层雄蕊现象的分类学意义是暂时的，尽管它清楚地说明了发育灵活性如何导致高度不同的花形态。
