the time I treated the known species of this genus (Am. Jour. Bot. 39: 418-423. 1952) five specific taxa were indicated. In 1957 Bremekamp added a sixth species, P. froesii, from Brazil (Meded. Bot. Mus. Herb. Rijks. Utrecht 141: 374-375. 1957). In this last paper he erects for Platycarpum, along with Henriquezia, a separate family, Henriqueziaceae, which he distinguishes from the Rubiaceae by the exalbuminous seeds, peculiar petiolar glands, absence of collecters on the inside of the stipules, zygomorphous androecium, and large size of the cotyledons in comparison with the axial part. According to Bremekamp, the genus Gleasonia is the only genus of Rubiaceae possessing cotyledons of large size in comparison with the axial part. "Whether or not these "petiolar glands" are unique in the flowering plants, as indicated by Bremekamp (loc. cit. p. 353), I cannot be positive, but it is probable that they appear elsewhere among other families of flowering plants.
For the present, I am retaining Platycarpum and Henriquezia in the Rubiaceae, along with Gleasonia. The following revised treatment of Platycarpum is based upon a study of newly available material which Bassett Maguire has kindly placed at m y command. These recent collections have resulted from various expeditions made by The New York Botanical Garden to portions of the Guayana Shield. Together with recent collections made by Sven Nilsson with me, they form the basis for the newly described taxa herewith presented, as well as for the emendations and supplementary notes on species previously described. In connection with this material, the "petiolar gland" has been found to be of some significance, even to the extent of the partial delimitation of species.
The genus, as at present constituted, is now known, largely from Venezuela, to extend from British Guiana (Mount Ayanganna) on the east, to the Vaupes River area of southeastern Colombia on the west, and southward into the Rio Negro drainage in the state of Amazonas of northern Brazil. In the Venezuelan area a large number of gaps are to be noted in the geographical distribution of the genus, but these eventually may be filled with future exploration. In the western and southern portions of its range, the species occupy lowland habitats along the streams from 100-800 m elevation above sea level, often at the base of such cerros as Yutaje and Moriche, or on the slope forest of Cerro Neblina, but at its eastern limits ascending to higher altitudes of the sandstone plateau of the Cerro Venamo area at 1300 m or on Mount Ayanganna in British Guiana at an elevation of 1000 m.
Altogether ten species, of which four are presented as new, and one new variety, are given in the following treatment.