Limiting factors of reproductive success in Bromus auleticus (Poaceae). 1. Flowering phenology, sexual expression, and pollen production

Abstract

The reproductive biology of Bromus auleticus was studied in three populations to identify factors related to flowering phenology and pollen production that could explain low fruit set. Flowering phenology was examined at the levels of population, plant, inflorescence, spikelet, and floret. Only one flowering event per year was recorded. Flowering proceeded downwards in the inflorescence and upwards within a single spikelet. Spikelets had on average 7.5 ± 1 chasmogamic, hermaphrodite florets and an apical, sterile or staminate floret. Each floret was open for 3 hours; pollen was shed over 10–75 minutes but the stigma remained receptive for 15–30 hours. There was ample overlap in flowering time among spikelets of the same inflorescence and among individuals of the same population; thus, both geitonogamy and cross‐pollination were possible. Hence, the limited female reproductive success of this species cannot be explained by its flowering phenology, as no mechanism exists (in space or time) that reduces or prevents the possibility of self‐fertilisation at the levels of the floret, spikelet, and/or inflorescence, or pollen interchange among individuals of the population. Neither the amount of pollen per flower or its fertility rate were limiting factors for adequate caryopsis setting.

Key words:

• Bromus auleticus
• floral phenology
• floret sexuality
• pollen production