Tetrastigma is a genus of flowering lianas in the grape family, Vitaceae, placed in the tribe Cayratieae alongside its closest relatives Cayratia and Cyphostemma. The genus comprises approximately 138 accepted species distributed across subtropical and tropical Asia, Malesia, and Australia, where they inhabit primary rainforest, gallery forest, monsoon forest, and moister woodland.
The plants climb by means of tendrils and bear palmately compound leaves. Tetrastigma species are dioecious — individual plants are either male or female — and the female flowers are distinctively marked by a four-lobed stigma, the feature that gives the genus its name (from Greek: "four stigmas").
Tetrastigma holds a remarkable ecological role as the exclusive host genus for the parasitic flowering-plant family Rafflesiaceae. Members of Rafflesia, Sapria, and related genera live entirely within the tissues of Tetrastigma roots and stems, breaking through the bark only to produce flowers. The most celebrated example, Rafflesia arnoldii, produces what is considered the largest individual flower of any plant on Earth. Research has also shown that Tetrastigma is the donor in multiple horizontal gene-transfer events to both Sapria and Rafflesia, representing an extraordinary case of inter-kingdom genetic exchange.
Etymology
The name Tetrastigma is derived from Greek, meaning "four stigmas", referring to the genus's distinctive four-lobed stigma on female flowers. This consistent morphological character sets the genus apart from its relatives in the grape family.
Distribution
Tetrastigma species are distributed across subtropical and tropical Asia, Malesia (the Malay Archipelago and associated islands), and northern Australia. Within this range they are plants of humid forest environments — primary rainforest, gallery forest along watercourses, monsoon forest, and moister woodland edges.
Ecology
Tetrastigma species play a uniquely important ecological role as the sole known hosts of the parasitic plant family Rafflesiaceae. The parasites — which include Rafflesia, Sapria, and Rhizanthes — lack roots, stems, and chlorophyll of their own and live as endoparasites entirely within Tetrastigma root and stem tissue, emerging only to flower. Rafflesia arnoldii, one of the most well-known parasites on this genus, produces the largest single flower in the world. Additionally, Tetrastigma has been identified as the donor in multiple horizontal gene-transfer events to Rafflesia and Sapria, making this host–parasite relationship one of the most studied examples of genetic exchange between flowering plants.
