The Synflorescence of Paspalidium rarum (Poaceae) and an Alternative Hypothesis about the Evolution of some Poaceous Inflorescences

Abstract

Synflorescences of the Australian species Paspalidium rarum (R. Br.) Hughes are described. Their structure in relation to other species of Paspalidium is discussed and their significance as an intermediate step in the evolution of inflorescences of Poaceae is considered. Such inflorescences comprise raceme-like structures which are derived from the typical inflorescences of Paspalidium by strong apical reduction of lateral axes. They possess two successive distal homogenised zones, the upper one bearing first-level short paracladia and the lower bearing truncate second-level short paracladia, and a proximal non-homogenised zone bearing more or less apically reduced long paracladia. The presence of such structures suggests a possible evolutionary pathway by which inflorescences such as those of Chloris, Cynodon, etc. could have evolved.