1963] 



BOTANY OF THE GUAYAXA HIGHLANDS PART V 



251 



Henriquezia, a separate family, Henrique ziaceae, which he distinguishes from 

 the Rubiaceae by the exalbuminous seeds, peculiar petiolar glands, absence of 

 colleters 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 my 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 arc 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. 



Key. to the Species of Platycarpum 



1. Leaves in 3 's. 



2. Petiolar gland absent or not evident ; lower surface of leaf -blades with soft dense 



pubescence of hairs up to 2 mm or more long. 10. P. eglandulosum. 



2. Petiolar gland evident; lower surface (excluding midrib and lateral nerves) of 

 leaf-blades either glabrous, glabrate, or with short hairs 1 mm or less long. 

 3. Petiole 2-4 mm long; lower surface of leaf -blades conspicuously pubescent; 

 plants of Amazonas, Brazil, and southeastern Colombia. 

 4. Petiolar gland quadrate; leaves rounded at apex, the blades 6.5-8.5 cm long; 

 lateral nerves of leaf -blades not prominently elevated beneath; peduncle 

 not pluricostate. 1. P. froesii. 



4. Petiolar gland shallowly semi-lunulate ; leaves subacute at apex, the blades 



6.5-14 cm long; lateral nerves of leaf -blades prominently elevated beneath; 



peduncle pluricostate. 2. P. schultesii. 



3. Petiole 7-15 mm long; lower surface (excluding midrib and lateral nerves) of 

 leaf -blades glabrous or sparsely puberulent; plants of Estado Bolivar, Ven- 

 ezuela. 



5. .Midrib and lateral nerves of lower side of leaf -blade glabrous or nearly so ; 



lower surface of leaf -blade glaucous or glaucescent; petiolar gland 1, 



