Notes on Bursera in South America, including a new species. Studies in Neotropical Burseraceae VII DOUGLAS C. DALY Daly, Douglas C. (New York Botanical Garden, Bronx, NY 10458-5126, U.S.A.). Notes on Bursera in South America, including a new species. Studies in Neo- tropical Burseraceae VII. Brittonia 45: 240-246. 1993.--Bursera inversa is the first new species of the genus to be described from South America in 90 years. The ecology of this species is remarkable because it is a large (to 25 m x 40 cm or greater) canopy tree of primary moist to wet lowland forest. It is easily distin- guished from its congeners by its large, obovoid fruits and bony pyrene. A key to the South American species of Bursera is provided. Key words: Burseraceae, Bursera, South American flora. Bursera Jacq. is a New World genus of some 100 species (Rzedowski & Guevara- Frfer, 1992). Like most of the tribe Bursere- ae, this group is characteristically found in semi-humid and (semi-)arid habitats. About 70 species of Bursera are endemic to Mex- ico, where it dominates much of the tropical deciduous forests, not only in terms of rel- ative density but also of relative diversity (Rzedowski, 1986). Four or five of the 13- odd Central American species are also found in Mexico. Another secondary center of di- versity and endemism is the West Indies, where perhaps all but two of the approxi- mately 14 species occurring there are en- demic. The family Burseraceae as a whole pre- sents several challenges to the systematist. Most of the taxa are dioecious; the small, actinomorphic, usually green flowers often differ only subtly among species of a given genus; and flowering material is scarce or lacking for many taxa because the flowers are difficult to see in the larger trees. In sev- eral genera, sympatry of closely related spe- cies frequently occurs. Chromosome counts are hard to obtain because there is resin in the developing anthers and because the seeds have short viability, making it difficult to collect them for germination and make sub- sequent counts from roots. The genus Bursera L. heaps additional complicating factors on top of these. Bark characters can be taxonomically useful, but bark material is rarely collected and even observations on bark characters are infre- quently noted on herbarium labels. Most if not all species of this group are deciduous, and typically they flower in the leafless state, thus making it extraordinarily difficult to match flowering and fruiting material. Flowers may be hermaphrodite or func- tionally staminate or pistillate, and the number of flower parts can differ depending on the gender of the flower as well as the subgenus to which the species belongs. The form of the fleshy, brightly-colored arillate structure that partially or completely en- velops the pyrene is taxonomically useful, but the pseudaril is at least as attractive to animals as it is to taxonomists, thus it is difficult to obtain specimens with mature fruits as well as intact pseudarils. Thereaf- ter, ants and herbarium pests are inclined to eat the pseudarils as well. Hybridization appears to be frequent in Bursera (e.g., Bul- lock, 1936; McVaugh & Rzedowski, 1965), in some cases producing species of hybrid origin (e.g., Rzedowski & Ortiz, 1988). The two taxa in the genus most recently de- scribed from South America were B. graveo- lens (Jacq.) Triana & Planch. var. villosula Brittonia, 45(3), 1993, pp. 240-246. ISSUED: 10 Sep 1993 9 1993, by The New York Botanical Garden, Bronx, NY 10458-5126