Population genomics reveal apomixis in a novel system: uniclonal female populations dominate the tropical forest herb family, Hanguanaceae (Commelinales)

The abundance of apomixis in tropical plant genera is poorly understood, and this affects the understanding of speciation and evolution. Hanguanaceae is a tropical monogeneric, dioecious plant family. All but two species are solitary herbs with no capability to spread vegetatively. Viable seeds are often produced when males have not been observed. Our aim was to investigate the presence of apomixis in Hanguana. We used reduced representation genomics to study phylogenetics and genetic variability in all populations of Hanguana in Singapore. We measured genome sizes and estimated ploidy levels in 10 species. Almost all taxa tested were genetically uniform (uniclonal) regardless of the extent of their distribution. The distribution of single clones over distinct localities supports our hypothesis of apomictic reproduction. Only one sexually reproducing native species was detected. Triploid and pentaploid states support our hypothesis that the type of apomixis in Hanguana is gametophytic. Population genomics tools offer a quick and cost-effective way of detecting excess clonality and thereby inferring apomixis. In the case of Hanguana, the presence of male plants is a strong indicator of sexual reproduction, whereas genome triplication is indicative of apomictic reproduction.