Revision of the Neotropical Genus Callaeum (Malpighiaceae)

Abstract

The monotypic genus Callaeum (Malpighiaceae) was proposed by J. K. Small in 1910 to accommodate an aberrant mascagnioid plant, Jubelina nicaraguensis Griseb. On the basis of flower, fruit, and leaf characters this genus is again recognized as distinct from Mascagnia, in which it was submerged by Niedenzu, and is augmented by the addition of most of the remaining members of Niedenzu's Mascagnia subg. Plagiogynixa, to which Niedenzu assigned C. nicaraguense. This makes necessary the new combinations Callaeum antifebrile, C. macropterum, C. malpighioides, C. psilophyllum, and C. septentrionale. In addition, C. chiapense is added by transfer from Stigmaphyllon, and three new species, Callaeum clavipetalum, C. coactum, and C. reticulatum, are described. Keys, descriptions, and citations of representative specimens are provided for the ten recognized species, and the segregation of this genus from Mascagnia is discussed. In the last revision of Mascagnia, Niedenzu (1928) divided it into the subgenera Mesogynixa (=subgenus Mascagnia) and Plagiogynixa, the latter set apart on the basis of its transversely dilated stigmas, few-flowered inflorescences, spherical buds, and three reduced posterior anthers. Earlier, Small (1910) had placed one of the members of Mascagnia subg. Plagiogynixa, M. nicaraguensis (Griseb.) Niedenzu, in the monotypic genus Callaeum, based upon jubelina nicaraguensis Griseb., a Central American plant with accessory fruit-wing appendages much like those found in Jubelina. Small did not explain his reasons for placing J. nicaraguensis in a separate genus, but did provide a key in which Callaeum was distinguished from other North American Malpighiaceae. Mascagnia, as circumscribed by Niedenzu, is a diverse collection of vines and shrubs with three-winged (rarely two-winged) mericarps. Palynological data, coupled with macromorphological information, indicate that the genus is a paraphyletic grouping, occupying the middle portion of a phylogenetic tree whose ultimate branches may include such genera as Hiraea, Triopterys, and even Malpighia (Lowrie 1982). Mascagnia subg. Plagiogynixa forms the nucleus of a natural group of species consistently different from other species of Mascagnia, and not necessarily most closely related to Mascagnia. The species of this subgenus, with one exception (see Excluded Taxon), are here segregated into Small's genus Callaeum, which is further augmented by the description of three new species. CALLAEUM Small, N. Amer. Flora 25(2):128. 1910.-TYPE: Callaeum nicaraguense (Griseb.)