Diversity, systematics, and evolution of Cynodonteae inflorescences (Chloridoideae – Poaceae)

The species of the Cynodonteae tribe show great morphological diversity in their reproductive structures. Previous studies where inflorescences were comparatively analysed in the context of phylogeny have shown that although grass inflorescences seem to be excessively variable, there are certain aspects of inflorescences that store relevant information on the evolution and systematics in Poaceae. We have analysed and compared the inflorescence structures of species belonging to the Hilariinae, Monanthochloinae, Scleropogoninae, and Muhlenbergiinae subtribes. Considering the most relevant morphological characters, the most recurrent types of inflorescences in the lineage were determined by means of a principal coordinates analysis. To understand the evolution of inflorescence morphology, ancestral reconstructions of inflorescence characters were performed using the Bayesian inference method. The results obtained demonstrate that the processes of homogenization and truncation might account for the diversity observed in adult inflorescences. Five different types of inflorescences were identified out of 36 theoretical possibilities. Amongst these, inflorescence type 1 (panicle of spikelets, with a terminal spikelet, non-homogenized, and bearing third- or higher-order branches) was found to be the most frequent in the studied group. Ancestral reconstructions of morphological characters allowed us to suggest that the ancestor of the group might have had an inflorescence with the form of a raceme of spikelets, non-truncated and bearing first-order branches. More complex inflorescences bearing no terminal spikelets and having branches of higher order might have diverged this lineage.

虎尾草族（Cynodonteae）各物种的繁殖结构展现出极高的形态多样性。此前已有研究在系统发育背景下对该族物种的花序开展比较分析，结果表明：尽管禾本科（Poaceae）的花序外观极具变异性，但仍存在若干可储存其演化与分类学相关信息的花序特征。
本研究对隶属于希拉里亚族（Hilariinae）、单花草亚族（Monanthochloinae）、硬秆草亚族（Scleropogoninae）以及穆伦贝格亚族（Muhlenbergiinae）的物种的花序结构进行了分析与比较。结合核心形态性状，本研究通过主坐标分析（principal coordinates analysis）确定了该支系中最常见的花序类型。
为解析花序形态的演化历程，本研究采用贝叶斯推断法（Bayesian inference method）对花序性状开展了祖先重建。所得结果显示，同质化与截短过程或可解释成体花序所呈现的多样性。
本研究从36种理论可能的花序类型中鉴定出5种不同的花序类型。其中，类型1花序（具顶生小穗、未发生同质化、着生三级及以上分枝的小穗圆锥花序）在本研究的类群中最为常见。
形态性状的祖先重建结果表明，该类群的祖先可能拥有未截短、仅着生一级分枝的小穗总状花序。而不具顶生小穗、着生更高阶分枝的更复杂花序类群，或由此支系分化而来。