Institute of Systematic Botany, University of Zurich, Zollikerstrasse 107, 8008 Zurich, Switzerland.
Am J Bot. 2009 Jan;96(1):22-66. doi: 10.3732/ajb.0800047.
Increasingly robust understanding of angiosperm phylogeny allows more secure reconstruction of the flower in the most recent common ancestor of extant angiosperms and its early evolution. The surprising emergence of several extant and fossil taxa with simple flowers near the base of the angiosperms-Chloranthaceae, Ceratophyllum, Hydatellaceae, and the Early Cretaceous fossil Archaefructus (the last three are water plants)-has brought a new twist to this problem. We evaluate early floral evolution in angiosperms by parsimony optimization of morphological characters on phylogenetic trees derived from morphological and molecular data. Our analyses imply that Ceratophyllum may be related to Chloranthaceae, and Archaefructus to either Hydatellaceae or Ceratophyllum. Inferred ancestral features include more than two whorls (or series) of tepals and stamens, stamens with protruding adaxial or lateral pollen sacs, several free, ascidiate carpels closed by secretion, extended stigma, extragynoecial compitum, and one or several ventral pendent ovule(s). The ancestral state in other characters is equivocal: e.g., bisexual vs. unisexual flowers, whorled vs. spiral floral phyllotaxis, presence vs. absence of tepal differentiation, anatropous vs. orthotropous ovules. Our results indicate that the simple flowers of the newly recognized basal groups are reduced rather than primitively simple.
对被子植物系统发育的理解日益深入，使得我们能够更准确地重建现存被子植物最近共同祖先的花及其早期演化。在被子植物基部出现了一些具有简单花的现存和化石类群，这令人惊讶，这些类群包括金粟兰科、金鱼藻科、水马齿科和早白垩世化石古果（后三者为水生植物），这给这个问题带来了新的变化。我们通过对形态学和分子数据得出的系统发育树上的形态特征进行简约优化，来评估被子植物的早期花进化。我们的分析表明，金鱼藻科可能与金粟兰科有关，而古果可能与水马齿科或金鱼藻科有关。推断的祖先特征包括两轮以上（或系列）的花被片和雄蕊，具有突出的背腹或侧面花粉囊的雄蕊，几个自由的、囊状的心皮，由分泌物封闭，延伸的柱头，外雌蕊联合点，以及一个或多个腹垂珠。其他特征的祖先状态是不确定的：例如，两性花与单性花，轮生花与螺旋状花序，花被片分化的存在与否，倒生胚珠与直生胚珠。我们的结果表明，新确认的基部类群的简单花是简化的，而不是原始简单的。
