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

Abstract

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.

Plastid phylogenomics and morphological character evolution of Chloridoideae (Poaceae)

“…The panicle is the most common inflorescence in Poaceae. Inflorescences were inferred to have evolved from simple to complex ( Pilatti et al., 2018 ). In the present study, the finding was the opposite.…”

“…Chloridoideae shows great morphological diversity, especially in inflorescence, spikelet and micromorphology ( Liu et al., 2010 ; Pilatti et al., 2018 ; Pilatti et al., 2019 ). These morphological characters are also important taxonomic features to classify Chloridoideae taxa ( Clayton, 1982 ).…”

“…An inflorescence consists of a group of flowers or clusters of flowers arranged on a stem. Inflorescence of Chloridoideae ranged from loose or dense panicles with a large number of spikelets to simple, single-spikelet inflorescences ( Pilatti et al., 2018 ). It is difficult to analyze the inflorescence evolution pattern because of the complexity ( Doust and Kellogg, 2002 ).…”

Synflorescence morphology of grasses with reduced terminal inflorescences: a case study of Jouvea (Cynodonteae, Chloridoideae, Poaceae)

“…In cynodonteae grasses, the correspondence between reduction of terminal inflorescence and increase of extra floriferous shoots has been registered in Distichlis acerosa, D. littoralis, and D. australis (Pilatti 2016), but has not been analyzed in the species of Jouvea. This kind of study requires not only an examination of the arrangement of flowers in terminal units (inflorescences), but also a structural analysis of the axis that bears them (=synflorescence) (Troll 1964, Weberling 1983, Vegetti & Anton 1996.…”

“…Inflorescence morphology in Cynodonteae displays enormous variation, including panicles of spikelets, racemes of spikelets, spikes of spikelets and inflorescences reduced to a single spikelet (Pilatti 2016. Inflorescences reduced to a single spikelet are homoplastic within Cynodonteae because they occur both in Jouvea and some species of Distichlis, including D. acerosa, D. australis and D. littoralis (Spegazzini 1902: 194) Villamil (1969 (Peterson et al 2016).…”