1963] 



BOTANY OF THE GUAYANA HIGHLANDS PART V 



159 



rotundati extus sparse glanduloso-setulosi et infra apicem minute unituberculati 

 ad margines dense cum glandulis sessilibus obsiti. Petala ca. 6 mm longa apice 

 setula unica glandulifera ca. 0.4 mm longa armata. Filamenta ca. 3 mm longa; 

 antherarum thecae ca. 2 mm longae, appendice dorsali descendente ca. 0.8 mm 

 longa. Stylus ca. 5 X 0.2 mm ; stigma truncatum ; ovarium non visum ; fructus 

 pedicellum indistinctum includens 6-7 mm longus ; capsula trilocularis apice 

 trigona et vix exsculpta. 



Type. Leaves green above, below bright red with white margin and midrib, 

 seen only once on wet mossy rock at Porkknocker Camp 2 on Partang River about 

 19 km above mouth, upper Mazaruni River basin, Pakaraima Mts., British Guiana, 

 alt. 625 m, 28 Jun 1960, Stephen S. TUlett, Carolyn L. TUlett, & Rufas Boyan 

 43929 (holotype NY; isotype US). 



All floral measurements were taken dry, the one flower of the collection not 

 being dissected. The sympodial zigzagging of the upper stem is more pronounced 

 in M. (infraction than in its near relatives, the angles formed being about 125°- 

 140°. M. anfractum seems intermediate between M. gi sm riac< urn and M. minus, 

 having the pseudo-alternate leaves of the former and the gland-tipped cauline hairs 

 of the latter; it approaches .1/. gesneriaeeum (with elliptic to oblong-elliptic 

 leaves) closer in foliage. Both relatives have esetulose petals. The group of 

 caulescent pubescent 4-merous species may be keyed as follows ■ 



1. Leaf blades above evenly pubescent. 



2. Pedicels 8-20 mm long; leaf dots 0.3 mm diam. M. vestitum. 



2. Pedicels 1.5-3 mm long; leaf dots 0.05 mm diam. M. brevipedicellatum. 

 ■ 1. Leaf blades above glabrous or pubescent only near margins. 



3. Petals tipped with a glandular seta. M. anfractum. 

 3. Petals esetulose. 



4. Internodes incurved-setulose. 



5. Petioles incurved-setulose ; leaf blade densely iucurved-ciliolate to the base. 



M. gesneriaeeum. 



5. Petioles glabrous; leaf margins sparsely ciliolate on apical 1/2 only. M. minus. 

 4. Internodes glabrous. 



6. Hypauthium outside setulose at torus and on wings below torus. M. rubescens. 

 6. Hypauthium outside setulose only at the torus. 



7. Leaf blade length/width ratio 2-2.3; petals 12-14 mm long. M. anyehioides. 



7. Leaf blade length/width ratio 3-4.5; petals 5.5 mm long. M. maguirei. 



Macrocentrum droseroides Triana. 



Hitherto known only from the eastern sandstone area, this delicate species 

 has now been collected in Canon Grande on Cerro de la Neblina (Maguire, 

 Wurdack, & Maguire 42234, 42517). The western population is distinguishable 

 qualitatively only by the presence of a caducous short glandtipped apical seta 

 on each petal. Quantitatively, the Neblina plants are generally more robust (the 

 leaf blades up to 5x2 cm) with sparsely glandular-setulose peduncles and 

 hypanthia ; in all these characters, however, there is overlapping with the 

 eastern population. 



Macrocentrum neblinae Wurdack. 



In a geographic reversal of the above-cited discovery of M. droseroides, M. 

 neblinae was recently collected by the Oxford 1959 British Guiana expedition in 

 the Potaro River Valley (No. 145). The leaf blades in the eastern material are 

 slightly more, elliptic than in the Neblina collections, but otherwise there is no 

 obvious differentiation. Both the above-cited examples show that some species 



