Description from Flora of China
Erythrodanum Thouars; Gomozia Mutis ex Linnaeus f.
Herbs, perennial, unarmed, sometimes fetid when bruised, often creeping and rooting at nodes. Raphides present. Leaves opposite, without domatia, marginally usually thickened and sometimes crisped; stipules persistent, interpetiolar and fused to petioles, triangular or bidentate. Inflorescences terminal and/or pseudoaxillary, 1-flowered, sessile or shortly pedunculate, ebracteate or sometimes with small involucre of bracts fused in pairs (i.e., calyculate) or of reduced stipules and leaves. Flowers bisexual, homostylous. Calyx limb truncate, 4-lobed, or reduced. Corolla greenish white, white, or pink, funnelform, glabrous inside; lobes 5, valvate in bud. Stamens 4, inserted near base of corolla tube, exserted; filaments developed; anthers basifixed. Ovary 2- or 4-celled, ovules 1 in each cell on axile placentas; stigmas 2 or 4, linear, exserted. Fruit orange, red, or black, drupaceous, ovoid or globose, fleshy, with calyx limb persistent; pyrenes 2 or 4, 1-celled, each with 1 seed, plano-convex, cartilaginous; seeds medium-sized, ellipsoid to plano-convex; testa membranous; endosperm scanty; cotyledons leaflike; hypocotyl hypogenous.
Phylogeography of the most widespread species Nertera granadensis (as N. depressa) was studied by Jakubowksy et al. (Evolution of Nertera. Poster presented at XVII IBC. 2005) using molecular data; they concluded that this species originated in New Zealand, where Nertera has its center of diversity, and dispersed independently to Australia, the Philippines, then SE Asia and Hawaii, and then Central and South America and eastward. They also suggested that N. nigricarpa may be better included within the circumscription N. granadensis, although species identity and circumscription were not the primary focus of their work so their sampling many not be adequate to address this. Nertera nigricarpa is distinguished primarily by its black rather than red mature fruit and was synonymized with N. granadensis by Liu and Yang (Fl. Taiwan, ed. 2, 4: 306. 1998), without comment; however, these species were separated by W. C. Ko in FRPS (71(2): 162-165. 1999). If these populations are treated as conspecific, this represents the only example known in Nertera of such fruit color dimorphism, which is known but uncommon in Rubiaceae. Nertera nigricarpa is provisionally separated here pending further study.
Liu and Yang (loc. cit.) and W. C. Ko (loc. cit.) described the flowers as bisexual or unisexual, but other authors reported the flowers of Nertera to be bisexual (e.g., Fosberg, Acta Phytotax. Geobot. 33: 73-83. 1982; Andersson, Fl. Ecuador 47: 11-12. 1993).
About six species: Antilles, Australia, Central, North, and South America, China, Indonesia, Malaysia, Pacific islands, Papua New Guinea, Philippines, Subantarctic islands (Tristan da Cunha), Vietnam; three species (one endemic) in China.
(Authors: Chen Tao (陈涛); Charlotte M. Taylor)