Monographs Details: Retiniphyllum scabrum var. ayangannense Steyerm.
Authority: Maguire, Bassett. 1965. The Botany of the Guayana Highland. Mem. New York Bot. Gard. 12 (3): 1-285.
Family:Rubiaceae
Description:Latin Diagnosis - A var. scabrum differt calyce apice subtruncato vel repando-denticulato; laminis foliorum ovali-oblongis vel oblongis apice rotundatis vel late obtusis basi rotundatis vel fere subcordatis 3-7 cm longis 1.6-2.5 cm latis, supra costa media subsulcata sparse strigillosa ceterum glabris, subtus dense pilis strumosis asperulo-hirsutis instrucits; floribus terminalibus 4-5-fasciculatis subsessilibus, pedicellis 1-3 mm longis; corollae tubo 28-29 mm longo, lobis 10-11 mm longis 5.25-6 mm latis.

Discussion:Some intergradations are found between var. scabrum and var. erythranthum. Among these may be cited Maguire, Steyermark d Maguire 46830 from Estado Bolivar, Venezuela with sparsely pubescent lower leaf surface, Cardona 2636 from Estado Bolivar, Venezuela, with a leaf shape similar to var. erythranthum, and Tillett, Tillett & Boyan 44916 from British Guiana, which resembles var. erythranthum in the sparsely pubescent lower leaf surface. A specimen which appears to represent a hybrid between Retiniphyllum laxiflorum and R. scabrum is Steyermark 59463 from Ptari-tepui, Estado Bolivar, Venezuela. In this collection the leaves are reticulate-nerved with the shape and texture as in R. laxiflorum, but the midrib of the lower leaf surface as well as parts of the lower surface are sparsely appressed-strigose. Also, the young or apical part of the stem is densely scabridulous or strigose, while the petioles are sparsely so. The 3-4 flowers are subfasciculate on pedicels 3-6 m m long, suggesting R. scabrum var. scabrum, but are slender, as in R. laxiflorum. The corollalobes, which are shorter than the corolla-tube, agree in this respect with those of R. scabrum var. scabrum, with measurements of 22-24 mm long for the corolla-tube (as compared with 25-29 mm in R. scabrum and 16-24 mm in B. laxiflorum) and 11-12 mm long for the corolla-lobes (as compared with 9-11 mm in R. scabrum and 10-20 mm in R. laxiflorum); the measurements thus show a somewhat intermediate condition between those of R. scabrum and R. laxiflorum. As regards the calyx-tube and hypanthium of the apparent hybrid, the length of the two combined (9-10 mm) approaches that of R. scabrum (with a combined length of 9-12 mm of the calyx and hypanthium) more closely than that of R. laxiflorum (with a length of 6-9 mm), although here again it is somewhat intermediate. The puberulent upper half of the calyx in the presumed hybrid specimen resembles more closely that found in R. laxiflorum than in that of R. scabrum, in which the calyx is densely hirtellous. Also, the more subtruncate, repand-denticulate summit of the calyx in the Steyermark 59463 collection suggests R. la.riflorum more than the usually toothed type found in R. scabrum (except var. ayangannense). In general, it m a y be stated that the vegetative aspect of this supposed hybrid plant is that of R. laxiflorum, but that the floral details resemble R. scabrum in some respects and R. laxiflorum in other details. The type of inflorescence suggests that of R. scabrum, but the delicate pedicels resemble those of R. laxiflorum.