Psathura has been recognized with several species from the Indian Ocean region in recent works by Bremekamp (1963, Madagascar) and Verdcourt (1989, Mascarene Islands). It is classified in the Psychotrieae tribe, and is characterized by its stipules that are usually quickly deciduous exposing a line of persistent, well developed colleters; usually gray to reddish brown drying color; and fleshy, white, drupaceous fruits with three to five triangular pyrenes. Psathura was acnowledged to be similar and closely related to Psychotria, and both of these authors noted that arguably it should be included in Psychotria but separated Psathura based on its 3-5-locular ovaries together with the systematic complexity of Psychotria that made identification of its relationships difficult. Andersson (2002) did not include Psathura in his study of the molecular systematics of Psychotria due to lack of sequence data, and suggested that it may belong to the Palicoureeae group rather than the Psychotrieae s. str. However its stipule morphology indicates its relationship with Psychotria s. str. The genus was studied in the molecular analysis of Razafimandimbison et al. (2014), who found the Psathura species were most closely related to various species of Psychotria and nested within the Psychotria clade and accordingly synonymized Psathura with Psychotria.
The separation of Psathura as a distinct genus based on its multilocular fruits by those authors followed the contemporary general view for the Rubiaceae, that this is a very unusual character that has been derived very rarely. However locule number varies in several genera of the Palicoureeae, with one or a few species having multilocular ovaries that appear to be derived within their respective genera (e.g., Notopleura, Palicourea), and with those multilocular species sometimes apparently related and sometimes apparently autapomorphic for this character. Thus, the inclusion now of Psathura within Psychotria is not seen as systematically or morphologically problematic today.
When the ovary locule number is disregarded, Psathura as circumscribed by Bremekamp and Verdcourt appears based on morphology to comprise three distinct species groups that do not appear not closely related to each other, and the morphological analyses of Razafimandimbison et al. (2014) also found Psathura species arranged in gorups with these groups separated within the cladogram of Psychotria. The species that were classified in Psathura from the Mascarenes have relatively small (1-5.5 x 0.7-3 cm), thick-textured leaves often with revolute margins, at least on the flowering stems, and short inflorescences enclosed by the leaves that have reduced bracts and ca. 2-11 flowers. The species that were classified as Psathura from Madagascar have larger leaves (4-21 x 1.5-13 cm) that are rather thick- to quite thin-textured and pedunculate lax inflorescences that extend well past the leaves and have reduced bracts and ca. 20-700 small flowers. The remaining species, Psathura seychellarum Baker, is found in the Seychelles and is generally similar to the plants of Madagascar in its well developed leaves and lax pedunculate inflorescence, but differs from both of the other species groups in its regularly developed inflorescence bracts and mostly persistent stipules.
Bremekamp (1963) recognized four species of Psathura in Madagascar, and Verdcourt (1989) recognized three in the Mascarenes with rather extensive variation detailed for Psathura borbonica; he recognized four varieties of this particular species, one found only in Mauritius and the other three only in Reunion. The species that were classified in Psathura from Madagascar are not well known, and are documented mainly by fruiting specimens; probably the flowering specimens are overlooked to some extent because the distinctive locule number is not readily evident on those.
For more information on individual species from Madagascar, see the Madagascar Project. (To access that data, in the upper right of this web screen, click on "Choose Project", and then the corresponding database from that list.)
Author: C.M. Taylor. The content of this web page was last revised 31 July 2014.
Taylor web page: http://www.mobot.org/MOBOT/Research/curators/taylor.shtml