Our knowledge of neotropical floristics is far from complete. Although plants from better collected areas may be well represented in herbaria, the number of recent floras and monographs of neotropical plants remains relatively low compared to other regions of the world. The neotropical Lauraceae (if not the tropical Lauraceae as a whole) are a good example of a little known group. This is in part because they are mostly tall trees with small flowers, and so are often undetected by collectors. Furthermore, even if trees are located by means of their aromatic wood, they are frequently sterile because flowering periods are short. Sterile collections are mostly indeterminable and are often set aside in piles in herbaria, and are rarely incorporated into monographic or even floristic works. Thus, not only is distributional information from herbarium specimens fragmentary, but also a great number of species tend to be known from a limited number of individuals making inferences about their distribution difficult.
Twenty three of the 41 species here treated are known from fewer than ten collections (Table I). These generally come from a single locality, or if from different localities they are often represented by a single individual in each. The fact that many species of Rhodostemonodaphne are known from a single locality may be reason to believe that there is a high degree of localized endemism in the genus–-alternatively, it may be the product of poor sampling. Unfortunately in most cases it is virtually impossible to distinguish between the two possibilities. The interpretation of gaps in the distribution of a species or pairs of species is similarly hampered. Gaps may represent disjunct distributions, or be an artifact of the lack of collections in the intervening areas. Lastly, relatively high species diversity in one area may be the product of high collecting densities rather than biodiversity “hot spots,” as has been shown for the Amazonian flora in general (Nelson et al., 1990).
The biogeographic regions I have adopted are for the most part congruent with previously proposed ones (Schnell, 1987, and references therein). For Amazonia in particular I refer to the subdivisions proposed by Prance (1976), with a few modifications. Unlike Prance, I treat the northern “Atlantic Coastal” and northern “Jari-Trombetas” subdivisions of Amazonia together, as the “northeastern South America region”, comprising northeastern Venezuela, the Guianas, and northern Amapá, Brazil. The region is separated from the Amazonian basin proper by the drainage divide of the Tumucumaque range and other minor mountain ranges separating Brazil from the Guianas. This and the presence of various species of Rhodostemonodaphne restricted to this region warrants its recognition as a separate biogeographical region, for the purpose of this discussion. The eastern Andean foothills, although part of the Amazon Basin, have often been treated as a separate entity because of their peculiar biota (Hueck, 1966; Cabrera & Willink, 1973; Schnell, 1987). Again, I treat this region separate from Amazonia, for there are various species of Rhodostemonodaphne that seem to be characteristic of this region.
Rhodostemonodaphne is restricted to the New World tropics. All but one species have relatively limited distribution ranges within South America. Only R. kunthiana is widespread in South America and extends north of the isthmus of Panama into Costa Rica. The majority of the species have distributions that are highly congruent with some of the major biogeographic regions of South America (Table II; see also species distribution maps).
The largest concentration of species is found in the lowlands and highlands of northeastern South America, comprising eastern Venezuela, the Guianas, and northeastern Brazil, as well as in central Amazonia. A total of 13 species are found in each of these regions, 12 of which (R. kunthiana excluded) are restricted to each region. The surroundings of Saül in central French Guiana appear to be an area with particularly high species diversity; seven of the 13 species found in the region have been collected in this relatively small area, and four have not been found elsewhere. Ten of the 13 are represented in French Guiana as a whole. Nevertheless, these high figures may result from recent intensive collecting in the country by the New York Botanical Garden and the Centre ORSTOM.
Within northeastern South American the species are distributed in a variety of habitats. Only five species are found in the northern coastal plains and none is endemic there. Most species are found in the interior highlands. Among these, two species, R. scandens and R. rufovirgata, have similar disjunct distributions, with collections from both Guyana and French Guiana, but not reported for Surinam (this may be due to lower collecting densities in the interior of Surinam). A few species appear to be restricted to the higher elevations of the interior and the Tumuc-Humac (French spelling) range on the border with Brazil. Rhodostemonodaphnetumucumaquensis, found on the Amazonian side of the range and on Mt. St. Marcell, an isolated mountain in southern French Guiana, is one of these. Rhodostemonodaphne miranda and R. mirecolorata, both restricted to the interior of Guyana, appear to be associated with sandstone formations of the Guayana highlands.
Two species are restricted to the Venezuelan Guayana highlands. These are R. steyermarkiana, from the Yutajé/Coro-Coro massif in the Gran Sabana, and R. celiana, from the Auyán tepuí in SE Venezuela. Although somewhat different architecturally (see morphological section), both species are low shrubs as is typical of the vegetation of the summits of these tabletop mountains.
The region with the second highest species diversity is the Amazonian basin proper. The variable R. praeclara s.l. is found throughout the region, including the “Xingú-Madeira” subdivision, where no other species of Rhodostemonodaphne is found. Another species with a broad distribution, but less so and restricted to the western part of Amazonia, is R. crenaticupula. The remaining Amazonian species have been collected either from a single locality or from larger areas that are presumably characterized by a particular habitat. Rhodostemonodaphnenegrensis is found along the Rio Negro and in the vicinity of Manaus, and is apparently associated with white sand forests of “black water” rivers. Another species commonly collected in white sand forests is R. licanioides, known from the vicinity of Iquitos. Rhodostemonodaphne curicuriariensis is known only from two collections from the Curicuriari river, a tributary of the Rio Negro. Although precise locality data for this species is unavailable, it seems to be associated with the sandstone mountain of Curicuriari from that locality. Rhodostemonodaphne peneia and R. recurva are known primarily from the vicinity of Manaus. Rhodostemonodaphne dioica has been collected in a small area in southwest Amazonia at the Bolivia-Brazil-Peru border. Rhodostemonodaphne kunthiana is spread across the Amazonian basin, but in localized patches within the region, such as the “Southwest”, “Solimões-Amazonas”, and “Manaus” subdivisions, and in the vicinity of the Amazon river delta.
The widespread Rhodostemonodaphne kunthiana is best represented, both in terms of number of collections and continuity of distribution, in what I here call the eastern Andean foothills. There too is where the greatest diversity of forms of this variable species are found. Rhodostemonodaphne synandra, a close relative of R. kunthiana, is restricted to this region, being found in four localities from Colombia south to Peru, in areas where R. kunthiana is also present. Rhodostemonodaphne napoensis and R. longipetiolata, also presumed relatives of R. kunthiana, are restricted to Napo Province of Ecuador, also in the Andean foothills. Rhodostemonodaphne longiflora and the southernmost representatives of R. kunthiana, are the only representatives of the genus from the Bolivian lowlands east of the Andes.
The strictly Andean species of Rhodostemonodaphne (R. kunthiana excluded) are found in the northern Andes in Ecuador, Colombia, and Venezuela, and are associated with cloud forests at elevations greater than 1500 m. The southernmost member is R. cyclops, from Ecuador. In Colombia, where the Andes trifurcate into three cordilleras separated by deep valleys, each cordillera has a separate species of Rhodostemonodaphne; these are R. frontinensis, R. laxa, and R. velutina, from the Cordillera Occidental, Cordillera Central, and Cordillera Oriental, respectively. In the Venezuelan Andes R. ovatifolia is present. Another cloud forest species, but in an area isolated from the core of the Andes, is R. avilensis, known from mountains near Caracas in Venezuela.
Rhodostemonodaphne antioquiensis is included in this region as an exception, for it is more of a lowland species found at ca. 500 m on the foothills of the Cordillera Central of Colombia. A population of R. kunthiana from the province of Oxapampa in Pasco, Peru, characterized by a long and dense indument, reaches elevations above 2000 m.
Only two species are found west of the Andes. One of them is the ubiquitous R. kunthiana. Concordant with a common biogeographical pattern, this species is found east of the Andes only to the north of the Huancabamba deflection in northern Peru. The other species is R. penduliflora, the only species of the genus from the Pacific lowlands of the Chocó region in Colombia. Rhodostemonodaphne kunthiana is also, as mentioned above, the only species of the genus with representatives in Mesoamerica.
Finally, three species are found in the Atlantic rain forest of southeastern Brazil. The more widespread of the three is R. macrocalyx, which has a range that extends from the southern tip of Bahia to just south of the tropic of Capricorn in Paraná. Rhodostemonodaphne anomala is known from two collections from the mountains of Petrópolis, near Rio de Janeiro, and possibly from a fruiting collection from southern Bahia. Rhodostemonodaphne capixabensis is restricted to the coastal sand forests (“restingas”) of Espírito Santo. A list of species by country, indicating the country endemics is provided (Table III).
Tables
- Table I. Habitat and distribution of Rhodostemonodaphne species
- Table II. Species of Rhodostemonodaphne by biogeographic region
- Table III. Species of Rhodostemonodaphne by country
