Aa erosa is a species of orchid in the genus Aa. It is endemic to Peru and blooms in late winter and early spring.

As a member of the Orchidaceae family, Aa erosa (synonymous to the name Altensteinia erosa) exhibits protandy based on anatomical observations. In plants, protandry occurs when the male reproductive structure releases pollen before the female parts can.

Written by Delsy Trjillo, Thassilo Franke, and Reinhard Agerer (2011), their anatomical studies confirm the presence of protandry in Aa erosa when trying to understand its evolutionary adaptations among orchids. Furthermore, this evidence is supported in Trujillo et al. (2024) research studies, which describe similar floral behavior in Aa olivacea, a closely related species.  

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