Alloteropsis is a genus of grasses in the family Poaceae (order Poales), native to the Old World tropics and subtropics. The genus is widely distributed across Africa, Asia, and Australia, with occurrences on islands in the Indian and Pacific Oceans. It comprises five accepted species: A. angusta, A. cimicina, A. paniculata, A. papillosa, and A. semialata.
Alloteropsis is notable among plants for containing species that use both C3 and C4 photosynthetic pathways. Most species employ variants of the C4 pathway, but one subspecies — A. semialata ssp. eckloniana — retains the ancestral C3 pathway. This unusual mix has made the genus a model system for studying the evolution of carbon concentrating mechanisms. Phylogenetic reconstructions suggest either that C4 photosynthesis arose independently in three lineages within the genus, or that a single C4 origin was followed by reversion to C3 in the eckloniana subspecies.
The genus is also remarkable as the first documented example of horizontal gene transfer between plant species not in direct physical contact. Genes encoding two key C4 enzymes, PEPC and PEPCK, were acquired from distantly related grass lineages that diverged from Alloteropsis over 20 million years ago and independently evolved C4 photosynthesis. All other genes expressed in the C4 leaf of A. semialata were vertically inherited from a common ancestor shared with the C3 subspecies.
Morphologically, members of Alloteropsis are typical grasses adapted to tropical and subtropical environments. The genus name derives from Greek allotrios ("strange") and opsis ("appearance"), likely reflecting its unusual combination of photosynthetic traits.
Etymology
The genus name Alloteropsis derives from the Greek allotrios ("strange") and opsis ("appearance"), presumably reflecting the unusual combination of photosynthetic pathways found among its species.
Distribution
Alloteropsis is native to the Old World tropics and subtropics, with species occurring across sub-Saharan Africa, the Indian subcontinent, Madagascar, Southeast Asia, China, northern Australia, and islands of the Indian and Pacific Oceans including New Guinea, the Solomon Islands, and New Caledonia. A. cimicina has also been sparingly naturalized in the southeastern United States.
Ecology
Alloteropsis is ecologically significant as a rare case of a plant genus containing both C3 and C4 photosynthetic species. Most species use C4 variants, but one subspecies — A. semialata ssp. eckloniana — uses the ancestral C3 pathway. This makes the genus a model for studying carbon concentrating mechanism evolution. Additionally, Alloteropsis represents the first documented case of adaptive horizontal gene transfer between plant species that are not in host–parasite contact: genes encoding the C4 enzymes PEPC and PEPCK were acquired from grass lineages that diverged over 20 million years ago.
