Monochaetum amistadense (Melastomataceae): A New Species from the Páramo of Costa Rica

Abstract

Monochaetum amistadense, a new species from the paramo of Costa Rica, is described, illustrated, and compared to its closest presumed relative, M. compactum. The distributional range of M. trichophyllum is extended from Panama to Costa Rica, and a diagnostic key is provided for the 10 species of Monochaetum now known from Costa Rica. The evolution of morphologically distinct taxa, often of limited geographic extent, has been a recurrent theme in the evolution of Monochaetum, a montane neotropical genus of some 45-50 species. The most recent regional monograph attributed 18 species of Monochaetum to Mexico and Central America, eight of which were reported from Costa Rica (Almeda, 1978). Collections of Monochaetum made in the Cordillera de Talamanca during the last decade have added two additional species to the Costa Rican flora. Monochaetum trichophyllum Almeda, which was described from and thought to be endemic to Panama, is now known from the Altantic slope of the Talamanca range (Limon: S side of unnamed cordillera between the Rio Terbi and Rio Sini, 2-4 airline km W of the Costa Rican-Panamanian border at 2,300-2,500 m, 11 Sep. 1984, Davidse et al. 28946, MO). The second addition, a distinctive novelty described below, is of special interest because it is the only known Costa Rican species confined to paramo habitats. Monochaetum amistadense Almeda, sp. nov. TYPE: Costa Rica. Limon: Cordillera de Talamanca, Cerro Kamuk massif, between Cerro Dudu and Cerro Apri, 9014'30-15'30N, 83003'30-04'30W, 23 and 26 Mar. 1984 (fl, fr), Davidse et al. 25932 (holotype, CAS; isotypes, CR, MO). Figure 1. Frutex 0.5-2 m altus; ramuli teretes sicut petioli inflorescentiaque dense pilis patulis barbellatis 0.5-1 mm longis induti. Petioli 0.5-1 mm longi; lamina 3-7.5 x 1.5-3 mm elliptica vel elliptico-ovata apice acuta basi obtusa vel rotundata, supra utrinsecus venas primarias densiuscule strigosa, subtus dense vel modice strigosa pilis 0.5-1 mm longis barbellatis, 3-nervata vel 3-plinervata. Inflorescentia terminalis 1-2 flora, flores 4-meri. Hypanthium (ad torum) 5-6 mm longum; calycis lobis 4.5-5.5 x 2-2.5 mm anguste oblongo-triangulares persistentes. Petala 10-12 x 5-7 mm obovata. Stamina dimorpha glabra, thecis subulatis, poro dorsaliter inclinato. Stamina maiora; thecae 7-8.5 mm longae; appendix dorsalis 33.5 x 0.5 mm, apice rotundato. Stamina minora: thecae 4.5-5 mm longae; appendix dorsalis 3 x 0.25 mm, apice hebeti-acuto. Ovarium 4-loculare apice modice setoso. Semina 0.5 mm longa, oblongo-arcuata. Erect, rigidly branched shrub 0.5-2 m tall. Distal internodes terete, copiously covered with spreading barbellate hairs 0.5-1 mm long, the nodes beset with flexuous spreading distally barbellate hairs 1.52 mm long. Older branches glabrate with reddish brown exfoliating bark. Mature leaves equal to somewhat unequal in size in each pair; petioles 0.5-1 mm long and 0.5 mm wide; blades membranaceous, entire, 3-7.5 mm long, 1.5-3 mm wide, elliptic to elliptic-ovate, 3-nerved or 3-plinerved, the apex acute, the base obtuse to rounded, the margin entire; adaxial surface copiously beset with a strigose indument of barbellate multicellular hairs in 4 longitudinal belts between the impressed primary veins