Phaius tetragonus is a large orchid that can reach 80 cm high, with a tetragonous stem, that has four well marked angles, which is covered at the base by numerous green bracts. The leaves are 20 cm long, lanceolate, narrow at the base and tapered upwards. Its long floral stem, forms 8 to 10 florets, and its sepals are shaped like spatulas. The petals are longer and narrower and are yellow-green in colour while the underside is reddish.
This species is mostly found in humid forests with a few patches also found in intermediate forests. Very localized terrestrial species. The flowers are spectacular during flowering.
Classified as ‘Critically Endangered’ on the IUCN Red List, it is not subject to specific conservation, but is protected under the Forest Restoration Project and in reserves. It has become rare due to habitat loss, collectors of orchids, soil disturbance by wild pigs and the invasion of exotic plants.
The Latin word tetragonous means "has four sides".
The population of this orchid has declined due to collectors of orchids.
Reported for Mauritius by Petit-Thouars in 1822.