Raritebe Wernham includes one morphologically rather variable neotropical species of shrubs and small trees found in wet forests in Central America and western South America. Raritebe can be recognized by its opposite or whorled, generally elliptic leaves; its interpetiolar, triangular to ovate, flattened, frequently bilobed stipules; its flowers grouped in terminal or occasionally axillary cymes; its salverform, creamy white to yellow corollas with slender tubes; and its fleshy purple or purple-black berries with numerous tiny seeds. The flowers are variously distylous or apparently homostylous, and may be nocturnal. The anthers usually the connective prolonged into an apical appendage. The corollas are usually rather fleshy, with the lobes valvate in bud.
Raritebe was described in 1917, but the genus was not well known and has sometimes been overlooked. It was long classified in the tribe Isertieae of the subfamily Cinchonoideae. However, the tissues of Raritebe contain raphides, while other genera of Isertieae lack these. Recent studies based on molecular data found that Raritebe is related to the neotropical genus Amphidasya as well as several paleotropical genera, notably Pauridiantha, and Raritebe is now classified in the tribe Urophylleae of the subfamily Rubioideae (Smedmark et al., 2008; Bremer & Eriksson 2009).
Raritebe is easily and often confused with Palicourea, which is quite similar in general aspect and many morphological details; however Palicourea can be recognized by its ovules solitary in each locule, and its drupaceous fruits with generally two large hard pyrenes. Raritebe is also quite similar to several species Coussarea, and these genera have been confused; however Coussarea can be recognized by its solitary ovule, and its fruits with a single rather large seed. Dwyer (1966) overlooked the genus Raritebe, which had not been reported previously from Panama, and described the new but synonymous genus name Dukea Dwyer for these plants.
Species-level taxonomy for Raritebe is complicated by morphological variation, both in general (i.e., small to large plants, leaves, inflorescences, and corollas) and within several particular regions where there seems to be exceptional variation. Raritebe was studied taxonomically by Kirkbride (1979), who recognized one species with two subspecies with distinct geographic distributions. subsp. palicoureoides includes the plants found from central Colombia to Venezuela, Peru, and western Brazil, which are distylous, while subsp. dwyerianum includes the plants found in coastal western Ecuador, coastal western Colombia, and Central America, which are homostylous. These homostylous flowers are unusual in Rubiaceae in their form, with the anthers and stigmas positioned at the same height within the corolla of a single flower, but at different heights in different flowers; also the anthers of these flowers are apparently coherent, or perhaps held together by some sticky substance. Kirkbride included all of the Central American plants in a single variety, even though these show an unusual range of variation in number of leaves per node, the size and texture of the leaf blade, stipule size, inflorescence arrangement (i.e., strongly congested or almost subcapitate to very lax or open), and calyx and corolla sizes. However Dwyer (1980) took an alternate view, and recognized six species of Raritebe in Panama. The initial review of specimens from this region suggests to each new taxonomist that there are patterns in this variation that deserve taxonomic recognition, but careful study then shows that the characters vary independently and continuously and in fact distinct species or varieties cannot be separated. The morphological characters found in these Central American plants are mostly not found in South American plants, and this may be an example of a species in the process of diversification in a relatively recently colonized region. Kirkbride also recognized two varieties of Raritebe palicoureoides subsp. palicoureoides: var. palicoureoides, found from central Colombia east and southward, and var. antioquianum, found only in northwestern Colombia. These were distinguished by their pubescence, with the leaf blades sparsely strigose to glabrate or glabrous on the lower surface and the flowers strigulose in var. palicoureoides, vs. the leaf blades hispid on the veins and sparsely hispidulous on the blade portion of the lower surface and the flowers hispidulous in var. antioquianum; with more specimens now available, pubescence variation seems less clearly patterned, and less well correlated with geographic range. Consequently these varieties have not been carefully distinguished in the specimens databased here and are not detailed on this web page; of course additional study may find that recognition of these or emended varieties is informative.
Unusual morphological is also found in plants of the western Amazon basin of Ecuador and Peru, which sometimes have axillary inflorescences; elsewhere the inflorescences are consistently terminal. These plants were separated as Raritebe axillaris, but were included in by Andersson (1999) in his floristic treatment of the genus, which is one of few studies available for . Its known range has been expanded significantly since Kirkbride's study, when it was only known from Costa Rica to north-central Peru.
Author: C.M. Taylor.
The content of this web page was last revised on 10 December 2010.
Taylor web page: http://www.mobot.org/MOBOT/Research/curators/taylor.shtml