Monographs Details: Retiniphyllum scabrum Benth. var. scabrum
Authority: Maguire, Bassett. 1965. The Botany of the Guayana Highland. Mem. New York Bot. Gard. 12 (3): 1-285.
Family:Rubiaceae
Description:Distribution and Ecology - Distribution. Red-flowered shrub of scrub forest and savanna margins on sandstone table mountains and plateaus of Estado Bolivar, Venezuela, and adjacent British Guiana, at alt. 750-2300 m. BRITISH GUIANA. Ayanganna Plateau, Upper Mazaruni River basin, S. S. & C. L. Tillett to R. Boyan 44916. VENEZUELA. Estado Bolivar: bosques de Bonnetia en la cumbre del Cerro Apacara, Cardona 1541; Bonnctia forest, northwestern part of summit of Abacapa-tepui, Chimanta Massif, Steyermark 74950; cumbre de Uaipan, K. D. Phelps 385; Cerro Uaipan, Cardona 2066, 2396; summit, Mount Auyan-tepui, Cardona 213; parte central del plato de Auyan-tepui, Foldats 2628; dwarf forest above Fila de la Danta, between Luepa and Cerro Venamo, Steyermark & Nilsson 300; northwest slopes, dwarf forest, Cerro Venamo, Steyermark & Nilsson 156; Caño Mojado east of north escarpment above upper falls, Toronotepui, Chimanta Massif, Steyermark & Wurdack 989; altiplanicie pantanosa de faldas inferiores del Aprada-tepui, Bernardi 800; southwest slope forest and savannas, Ptari-tepui, Maguire & Wurdack 33914; thickets on Mesa Grande, Ili-tepui, Maguire 33345, 33325A; lower slope forest, Ilu-tepuí, Maguire 33249.

Discussion:The name R. scabrum Benth. has been neglected since 1841. It is obvious that the plants of the Gran Sabana of Estado Bolivar, Venezuela match the description of Bentham and must replace the name of R. erythranthum Standi., previously used for the plants of the Gran Sabana. A n examination of type material of R. erythranthum Standi, from Cerro Duida, Territorio Amazonas, Venezuela, shows that it is not conspecific with R. scabrum, but can be separated from the latter at least varietally. In describing R. erythranthum, Standley was apparently unable to see the resemblance existing between the plants from Cerro Duida and the Schomburgk specimen of R. scabrum, and in his treatment of Rubiaceae of Venezuela (Field Mus. Bot. Ser. 7: 401. 1931) placed the name in alphabetical order without being able to match it with anything known from Venezuela. Obvious differences exist between typical R. scabrum Benth. of Estado Bolivar, eastern Venezuela, and R. erythranthum Standi, of Cerro Duida and other cerros of Territorio Federal Amazonas, western Venezuela. In R. scabrum. var. scabrum the leaf-blades of the fertile shoots are elliptic- or obovate- to lanceolate-oblong and abundantly scabrid-hirsutulous on the lower surface, and the calyx-lobes are 0.75-2 mm long. On the other hand, the plants of Cerro Duida and other cerros of Territorio Federal Amazonas, which fit Standley's description of R. erythranthum, have the leaf-blades of the fertile shoots more oval or broadly elliptic-ovate with the lower leaf surface usually glabrous or with less abundant trichomes, which are not strumose nor scabrid, and the calyx-lobes are only 0.75 mm long. Moreover, the plants of R. erythranthum have nearly sessile or only shortly pedicellate flowers with pedicels only 1-2.5 mm long, whereas the pedicels in typical R. scabrum are 2-7 mm long. Finally, it is to be noted that plants from Mount Ayanganna, British Guiana, represent still another departure from typical R. scabrum, as well as from R. erythranthum, in having a truncate, merely repand-denticulate summit of the calyx, instead of ovate or broadly triangular calyx teeth or lobes of the other taxa. The shape of the leaf-blades of the plants from Mount Ayanganna, as well as their type of pubescence, resemble most closely those of typical R. scabrum. A close study of all this material has led to the present interpretation in treating this complex as consisting of three varieties, as delimited in the key under R. scabrum.
Distribution:Guyana South America| Venezuela South America|