, Volume 159, Issue 1, pp 1-13

Flowering phenology and reproductive output in two sister species of Ferocactus (Cactaceae)

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Flowering phenology is often strongly constrained by phylogenetichistory: many closely-related plants have very similar phenologies. On theotherhand, divergent flowering phenologies can function as isolating mechanisms,which may be reinforced if related plants occur sympatrically. I investigatedflowering phenology and reproductive output of sister species of barrel cacti,Ferocactus cylindraceus and F.wislizeni, where they occur sympatrically in the Sonoran Desertsurrounding Tucson, Arizona. Ferocactus cylindraceus beganblooming in May, and continued until early or mid-October, with a bimodalpattern of flowering amplitude. Individuals in the study population weremoderately well-synchronized phenologically. Ferocactuswislizeni began blooming in July, and also continued until early ormid-October, with a single peak of intensity; individuals in the studypopulation were well- synchronized phenologically. In both species, the vastmajority of individuals bloom every year. Plant size was positively correlatedwith flowering amplitude in both species, and with flowering onset inF. wislizeni. The study population of F.cylindraceus was strongly affected by a flower-eating caterpillar inall years, with the earliest flowers most likely to be destroyed. ForF. wislizeni, seed number per fruit was highest forflowersopen in the middle of the blooming season in 1998. Other components ofindividual plant phenology, including among-plant synchrony, had littleinfluence on reproductive output.