Three New Species of Rhipidocladum from Mesoamerica

Abstract

Rhipidocladum clarkiae Pohl and R. pacuarense Pohl are described from Costa Rican flowering material and R. panamense Pohl is described from flowering specimens from Panama. The genus Rhipidocladum was erected by McClure (1973) to include species of bamboos previously assigned to Arthrostylidium, Arundinaria, and Ludolphia. The species of Rhipidocladum are slender and graceful. At each midculm node, they bear an adnate triangular flat meristematic branch that produces numerous foliage-bearing lateral branchlets in a fan-shaped (apsidate) array. The genus is differentiated vegetatively from Merostachys, which has a similar branchlet array, by the nature of the main culm leaves. In Rhipidocladum, the base of the erect culm blade is as wide as the apex of the sheath and adnate to it. In Merostachys, the reflexed blade of the culm leaf is pseudopetiolate and much narrower than the sheath apex. The species of Rhipidocladum are slender bamboos, ranging from 2 to 10 m or more in length and 1 to 5 cm diam. They inhabit mesic sites in moist forests and are found on canyon walls and river banks at low and middle altitudes. The genus ranges from southern Mexico to northern South America, with one species reported from Brazil. McClure indicated that his genus included 11 species and offered a key to distinguish some of these. One species, R. verticillatum, has since been transferred to a new genus, Actinocladum, by Soderstrom (1981). With the addition of these three new species, the current number is 13. Mesoamerican species of Rhipidocladum are not well known because of their erratic blooming cycles. Recent gregarious flowering of two Costa Rican species and one from Panama has allowed differentiation of species previously known only in the vegetative condition. Two of these species, R. clarkiae and R. panamense, are distinct from the remaining species of the genus because of their extremely large number of fiiform branches. The third, R. pacuarense, is most closely related to R. bartlettii of the Peten of Guatemala and Chiapas, and their differences are stated in Table 1. In the absence of adequate type material of many of the species, detailed comparisons with the remaining species cannot be made. The key given by McClure (1973) offers the best separa-