While collecting in the northern hills of the Dominican Republic, I found a
vine that to me looked like a species of Platygyne, a genus heretofore endemic to Cuba.
In trying to name it I noticed that Tragia biflora Urban corresponded to m y specimens,
and that it was indeed the correct name. I then studied the differences
between Tragia and Platygyne. It is indeed very difficult to tell one genus from
Several species of Tragia have been reported from the West Indies. The
ubiquitous T. volubilis L. being the most widespread; Cuba has two more species
of very restricted endemism, T. cubensis Urban (Fedde Repert. 28: 226. 1930)
and T. gracilis Grisebach (Nachr. Ges. Wiss. Goett. 1865: 176. 1865), this last
species known only from the type collection. In 1928, Urban described Tragia
biflora [Ark. Bot. 22A(8): 62. 1928] from Haiti, the type specimen coming
from Massif de la Hotte, in the southern peninsula. Several other collections seem
to extend the range; Ekman collected it again in the Dominican Republic, near
Sosua on the northern coast, and I found it in the same region at El Choco, E of
Sosua, where it is called Guao because of the painfully stinging hairs on the leaves
Pflanzenreich [IV. 147. IX-XI(68): 1919] Pax and Hoffmann note the
following differences between Tragia Linnaeus and Platygyne Mercier: the number
of stamens, the shape of the receptacle (globose or flat). According to Pax, Tragia
has 3 (2 or 1 by abortion) stamens, but some species have from 30 to 50; the
filaments are short, broad and more or less united at the base, which is true only
for a few species, and the receptacle is flat. Platygyne, according to the definition,
has a globose, hairy receptacle, fewer (5-10) stamens and the filaments are slender
and attached separately to the receptacle; many of these characters are quite
inconsistent, when the number of stamens is considered, the presence or absence
of a receptacle, the length and width of the filaments, the shape of the styles; all
these characteristics seem to be quite variable.
Platygyne was segregated from Tragia by Mercier in 1830, based on Cuban
specimens. The major differences seem to be in the number of stamens, the presence
of a hairy receptacle, the wider and emarginate styles. While studying the genus
for the Flora of Cuba, I found that besides the very common Cuban species P.
hexandra (Jacq.) Muell.-Arg., there was another described species, P. volubilis
Howard (Jour. Arnold Arb. 28: 120. 1947). Studying the material collected in
Cuba, I described three new species: P. leonis, P. dentata and P parvifolia (Contr.
Ocas. Mus. La Salle 11: 6-8. 1952). All except P parvifolia have a hairy receptacle
and 5-10 stamens; P. parvifolia has 10-14 stamens on a glabrous receptacle; this
last species extends the generic concept and suggests a link between Tragia and
Platygyne. Can Platygyne be kept as a different genus?