Monographs Details: Graffenrieda irwinii Wurdack
Authority: Maguire, Bassett & Wurdack, John J. 1964. The botany of the Guayana Highland--Part V. Mem. New York Bot. Gard. 10: 1-278.
Family:Melastomataceae
Description:Latin Diagnosis - G. caryophylleae Triana affinis sed ramis subalato-quadrangularibus, petiolis alatis, inflorescentiae bracteis magnis ad anthesim persistentibus. Rami alato-quadrangulares alls crassis 1-1.5 mm altis cum petiolis inflorescentiis bracteis extus hypanthiisque sparse appresso-furfuracei demum glabrati. Petioli 1.5-2 cm; lamina 12-17 X 4.5-6.5 cm elliptica apice hebeti-acuta basi acuta et usque ad petioli basim anguste decurrens coriacea, trinervata nervis primariis lateralibus 2-3 mm inframarginalibus nervis secundariis 4-6 mm inter se distantibus tertiariis invisis, supra glabra subtus in nervorum primariorum axillis minute barbellato-setulosa et in superficie densissime punctulis minutis pallide flavidis obsita alioqui glabra integra. Panicula 15 cm longa pyramidato-oblonga ad nodos conspicue bracteata; bracteae 25 X 12 mm vel distaliter 10 X 8 mm elliptica vel rotundato-elliptica intus glabrae naviculares certe ad anthesim persistentes. Flores 5-meri sessiles ad ramorum brevium apices glomerati. Hypanthium (ad torum) 5 mm longum; calyx primum ca. 2-2.5 mm altus clausus apiculatus demum in lobos 3-4 irregulariter dehiscens. Petala 12-13 X 7-8.5 mm obovata apice asymmetrice lateque obtusa glabra. Filamenta 6 mm longa; antherarum thecae 5 mm longae curvatae convolutae appendice dorsali 1.3 mm longa acuta. Stylus 9.5 X 0.5 mm glaber; stigma punctiforme; ovarium 3-loculare liberum apice truncatum.

Discussion:

Type: Shrub to 4 m, corolla white, in rocky soil overhanging brink adjacent to Kaieteur Falls, Potaro River, British Guiana, 17 Jan 1954, H . S. Irwin 117 (holotype US 2143648).

G. caryophyllea has obscurely rounded-quadrate to terete branches, non-alate petioles, and minute deltoid early-caducous inflorescence node bracts about 1 mm long. The flowers of the two taxa are alike. G. caryophyllea is apparently to be found on most of the crystalline monadnocks of the upper Rio Negro drainage, as well as on the Gran Sabana and in several cumbres (Auyan-tepui, the Chimanta Massif, Guaiquinima, Duida, and Yutaje). The amorphous lower leaf surface indument varies in amount and persistence, with most (but not all) cumbre collections having the deepest and most persistent. Generally, the cumbre material has slightly smaller flowers than the lower-elevation specimens, but one large Rio Parguaza monadnock series (Wurdack d; Monachino 41025) has slightly smaller flowers than any cumbre number along with quite glabrous foliage. Minute punctulae like those of the leaves of G. irwinii may also be seen in the more glabrous collections of G. caryophyllea (cf. Maguire & Maguire 35146). Triana's and Cogniaux' descriptions of the "4-merous" flowers of G. caryophyllea are quite misleading, as examination of an isotype (NY) and the numerous recent collections shows almost exclusively 5-mery.