These plants were previously included in Morinda, which was previously circumscribed more broadly as a pantropical group of shrubs, trees, and lianas. However Razafimandimbison et al. (2009) surveyed Morinda and related genera using molecular data, and concluded that the species fall into two distinct clades, which they treated as Morinda s. str. and Gynochthodes. In Madagascar, Morinda retains one pantropical species, M. citrifolia, while the remaining species have been transferred to the Paleotropical genus Gynochthodes. In general Gynochthodes comprises lianas with polygamous to dioecious flowers and the corolla tube shorter than the corolla lobes. Additionally these species have opposite leaves, stipules that are interpetiolar to shortly tubular, distylous flowers, tubular calyx limbs, corollas with 5-6 lobes, and fleshy multiple fruits that are generally white to yellow when ripe and are composed of the fused ovaries of numerous flowers. The fruit of each flower has generally 2-4 seeds, which are enclosed in pyrenes. Razafimandimbison et al. (2009) characterized the breeding biology of this genus based on studies of the Pacific and southeast Asian species; the breeding biology of Madagascar species has not been studied. One Madagascar species was included in their analysis, G. retusa, which was found to be related to several species from the Pacific. There is some variation in Gynochthodes and related genera (e.g., Caelospermum) in degree of fusion of the flowers in an inflorescence, and there appears to be some variation in this feature among the Madagascar plants (e.g., Rakotovao 162 has the flowers almost free).
Two morphologically quite distinct species of Gynochthodes have been named and separated in Madagascar, but each of these groups of plants most likely includes several species. These two species are treated here in their current, very broad circumscriptions until they are studied in more detail. The name G. umbellata is used here provisionally for one of these species; this species is currently circumscribed as a widespread in Asia and some Pacific Islands. The name Morinda rigida Miq. has been used in herb. for plants that are not clearly separable (at this time) from G. retusa. The name M. rigida applies to plants from Indonesia, which are generally similar to the Madagascar plants but the southeast Asian plants can be separated by their acute leaf tips, and from many of the Madagascar plants by their calyx limbs ca. 1-2 mm long. Here the name Morinda rigida is provisionally excluded from the Madagascar flora.