Jeiter Julius, Weigend Maximilian, Hilger Hartmut H
Nees-Institut für Biodiversität der Pflanzen, Rheinische Friedrich-Wilhelms-Universität Bonn, Meckenheimer Allee 170, D-53115 Bonn, Germany
Biologie-Botanik, Freie Universität Berlin, Altensteinstraße 6, D-14195 Berlin, Germany.
Ann Bot. 2017 Feb;119(3):395-408. doi: 10.1093/aob/mcw230. Epub 2016 Dec 26.
The detailed relationships in Geraniales in their current circumscription have only recently been clarified. The disparate floral morphologies and especially the nectaries of the corresponding group have consequently not previously been studied in a phylogenetic context.
The present study investigates floral and especially nectary morphology and structure for representatives of 12 of the 13 currently accepted genera in the five families of the Geraniales. Flowers were studied using light microscopy and scanning electron microscopy.
The data demonstrate the derivation of even the most disparate floral morphologies from a basic pentamerous and pentacyclic organization, with an obdiplostemonous androecium and receptacular nectaries associated with the antesepalous stamens. Divergent morphologies are explained by modifications of merosity (tetramerous flowers), symmetry (several transitions to zygomorphic flowers) and elaboration of the nectaries into variously shaped outgrowths and appendages, especially in Francoaceae. The divergent development of nectar glands ultimately leads to either a reduction in their number (to one in some Geraniaceae and Melianthaceae) or their total loss (some Vivianiaceae).
Floral morphology of the Geraniales shows a high degree of similarity, despite the variation in overall floral appearance and nectary morphology. A hypothesis on the transformation of the nectaries within the Geraniales is presented.
牻牛儿苗目目前界定范围内各分类群之间的详细关系直到最近才得以厘清。因此，此前尚未在系统发育背景下研究过该类群截然不同的花形态，尤其是相应类群的蜜腺。
本研究调查了牻牛儿苗目五个科中目前公认的13个属里12个属的代表植物的花，尤其是蜜腺的形态和结构。利用光学显微镜和扫描电子显微镜对花进行研究。
数据表明，即使是最截然不同的花形态，也是从基本的五基数和五轮式结构衍生而来，具有对萼雄蕊的异基数雄蕊群和与萼前雄蕊相关的花托蜜腺。不同的形态可通过基数的改变（四基数花）、对称性（向两侧对称花的多次转变）以及蜜腺演变成各种形状的突出物和附属物来解释，尤其是在方枝树科中。蜜腺的不同发育最终导致其数量减少（在某些牻牛儿苗科和蜜花科中减少到一个）或完全消失（一些智利藤科植物）。
尽管牻牛儿苗目的花整体外观和蜜腺形态存在差异，但其花形态仍表现出高度相似性。本文提出了关于牻牛儿苗目蜜腺转变的假说。
