Reproductive ecology of the threatened "star cactus" Astrophytum ornatum (Cactaceae): A strategy of continuous reproduction with low success

Abstract

Background: There are no previous studies on the reproductive biology of the endemic and endangered cactus species Astrophytum ornatum. Questions: Is flowering continuous or episodic? What are the breeding and mating systems and what floral visitors are associated? and Does the reproductive success change over time? Study species: Astrophytum ornatum (Cactaceae). Study site and years of study: Observations from 2010 to 2011, in the highest density population of A. ornatum in Metztitlán Canyon (Hgo. México). Methods: Monthly surveys and monitoring of reproductive structures. Tracking flowers in anthesis. Controlled pollinations to determine the mating system and determination of the Outcrossing Index (OCI), the pollen /ovule ratio and breeding system. Results: Astrophytum ornatum produced flower buds throughout the year, but 89.2% of them were aborted. Four events of ephemeral flowering population were presented per year. The species is self-incompatible and controlled pollinations indicated pollinator limitation of several bee species. The OCI indicates that the species is facultative xenogamous, and pollen/ovule ratio indicates obligate xenogamy. On average there were 54 seeds/fruit and individuals produced 4 fruits/year. Conclusions: The continuous production of buds had rarely been reported for cacti. Intrapopulation bloom is one of the shortest recorded for the family and it produces high floral synchrony. The low number of seeds / fruit and flowers / individual, coupled with the narrow niche breadth of species and various anthropogenic factors place Astrophytum ornatum as a susceptible species to be extinct.