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.

狗牙根族（Cynodonteae）物种的生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花序（inflorescence）开展比较分析，结果表明：尽管禾本科（Poaceae）的花序外观变异极为丰富，但其中部分特征蕴含着与该科演化及分类学相关的重要信息。本研究对隶属于希里草亚族（Hilariinae）、单穗草亚族（Monanthochloinae）、硬草亚族（Scleropogoninae）以及穆伦草亚族（Muhlenbergiinae）的物种的花序结构进行了比较分析。结合核心形态性状，本研究通过主坐标分析（principal coordinates analysis）确定了该演化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（Bayesian inference）方法对花序性状开展了祖先性状重建（ancestral reconstruction）。研究结果显示，花序的均质化与截短过程或可解释观测到的成体花序多样性。本研究从36种理论花序类型中鉴定出5种不同的花序类型，其中类型1花序（具顶生小穗（spikelet）、未发生均质化、具三级及以上分枝的小穗圆锥花序（panicle of spikelets））在研究类群中最为常见。祖先性状重建结果表明，该类群的祖先可能拥有具一级分枝、未发生截短的小穗总状花序（raceme of spikelets）。而不具顶生小穗、具高阶分枝的更复杂花序类群，或从该支系中分化而来。