Uncovering the inflorescence evolution of Eleusininae (Cynodonteae: Chloridoideae: Poaceae)

Abstract

Inflorescence forms in grasses lead to a general assumption that their evolution is random. We reconstructed the ancestral inflorescence for Poaceae subtribe Eleusininae and outlined possible evolutionary pathways to test the hypotheses of (1) non-directionality in grass inflorescence evolution and (2) an evolutionary direction from complex to simpler inflorescence architectures in this lineage. By studying early stages of inflorescence and spikelet development, we investigated ontogenetic changes that may correlate with evolutionary pathways identified. The approach presented here indicates that the current diversity of inflorescences found in Eleusininae is probably a result of two distinct evolutionary pathways. The main path involves a multi-staged course with shortening of main axis internodes first, followed by a decrease in number of primary branches and florets per spikelet. We postulate that reduced elongation of the internodes may affect the apical and axillary meristems performance, which in turn promotes a decrease in the number of primary branches and floret per spikelet. Current diversity in inflorescences of Eleusininae may be a consequence of a reductive evolution. We found that the evolutionary directionality of inflorescences in Eleusininae may be associated with developmental events that affected inflorescence morphology at early stages.