species exhibiting genetic sex determination via the UV sex chromosome sex determination system. Some monoicous moss species such as Splachnum ampullaceum exhibit environmental sex determination during early development, with low light, low pH, and low nutrient availability all promoting male development. In the presence of auxin, a widespread plant hormone, or gibberellins, compounds similar to Antheridiogen in ferns, both female and male individuals invest more in sexual structures (antheridia and archegonia). Environmental sex determination in moss is fundamentally different from the spatial segregation of sexes, the occurrence of environmentally mediated sex ratios in moss patches, observed in sexually static moss species. Spatial segregation of the sexes in mosses is caused by differential survival rates between sexes as a result of the competitive advantage of female moss. This leads to female dominated populations maintained by asexual reproduction and minimal sexual reproduction. In contrast, environmental sex determination is the dynamic development of females or males in different environmental conditions. Angiosperms Many angiosperms exhibit sequential hermaphroditism, meaning that they can switch sexes continually throughout their life based on the current conditions and resource availability to optimize fitness each flowering season. But sequential hermaphroditism and environmental sex determination are not mutually exclusive. For example, Catasetum viridiflavum, an epiphyte (plant that grows on another plant) in the Orchidaceae family exhibits sequential hermaphroditism where the younger, smaller individuals have male inflorescences and the older, larger individuals have female inflorescences, but sex expression is also strongly influenced by light intensity. Individuals in high light are more often female and individuals in the low light are more often male, regardless of size. In higher light, individuals produce more ethylene, a common plant hormone, which promotes the formation of female flowers. References Sex-determination systems