Glume absence in the Orcuttieae (Gramineae: Chloridoideae) and a hypothisis of intratribal relationships

This study addresses glume absence in tribe Orcuttieae. In Orcuttia califomica, 0. inaequalis, and 0. viscida, all spikelets possess two glumes except for the terminal spikelet of the inflorescence, which lacks both glumes. In 0. pilosa and Tuctoria greenei the terminal spikelet lacks only the first (proximal) glume, whereas in 0. tenuis, T. fragilis, and T. mucronata both glumes are developed on all spikelets. This is the first report of glume absence in species of Orcuttieae other than Neostapfia colusana, which has been long reported to lack both glumes on all spikelets. A hypothesis of phylogenetic relationships in the tribe is presented and characters involved are discussed. We hypothesize Neostapfia to be sister to a Tuctoria/Orcuttia clade, and Tuctoria to be a grade leading to a monophyletic Orcuttia.