Manual de Plantas de Costa Rica 187 
112-181 spp./ha (Huber, 1996; Weissenhofer, 1996) and 186—217 spp./ha (Castillo, 
1996, in Acosta, 1998) for individuals above 10 cm DBH, and 149-201 spp./ha (N. 
Zamora V. & R. Aguilar, unpubl. data) for individuals above 5 cm DBH. Furthermore, 
there are considerable differences of diversity within the area, depending on topogra- 
phy (ridge-top, valley, slope, or coast). At least in terms of trees, these forests appear 
equally or more diverse than those of the non-seasonal Caribbean lowlands. But the 
Caribbean lowlands are manifestly richer in epiphytes and ferns; moreover, in the Sara- 
piqui area, tree diversities as high as 203 spp./ha (individuals > 10 cm DBH) have been 
measured in one plot at 300 m elevation, and tree-diversity values from the Caribbean 
lowlands at 100-500 m elevation (Lieberman et al., 1996) are comparable to those 
from the Osa Peninsula. Thus, our impression that the Osa Peninsula has especially 
high diversity needs more careful evaluation. 
Vegetation types within the interior of the Osa Peninsula have already been briefly 
discussed by others (Quesada Q. et al., 1997; Weissenhofer et al., 2001; Kappelle et al., 
2003), so we will only briefly refer to them. The area along the neck of the peninsula, 
between Los Mogos and Rincon, appears to be particularly rich in members of the 
legume family, such as Balizia elegans, Bauhinia sp. nov., Copaifera camibar, Dalber- 
gia frutescens, Inga venusta, Macrolobium costaricense, Mimosa myriadenia, Newtonia 
suaveolens, Parkia pendula, Peltogyne purpurea, Senna spinescens, Uribea tamarin- 
doides, and Zygia cognata. Many of these species are also known from the neighbor- 
ing and floristically similar areas of Piedras Blancas National Park and the Golfito Na- 
tional Wildlife Refuge. For some (Copaifera camibar, Zygia cognata), as many as 20 
individuals/ha have been recorded (N. Zamora V. & R. Aguilar, unpubl. data). Copaifera 
camibar, which when published was considered endemic to the peninsula, has recently 
been discovered in the Venezuelan state of Amazonas, between Puerto Ayacucho and 
Gavilan (80—100 m elevation), where it is also often quite common (Berry et al., 1997). 
This is just one of many examples demonstrating the special floristic affinities between 
the Osa Peninsula and northern South America. 
The three highest points on this peninsula, which range from only 617 to 745 m, 
contain elements (sometimes relatively abundant) characteristic of montane or cloud 
forests, usually of much higher elevations, e.g.: Alfaroa guanacastensis, Anthurium 
hoffmannii, Bactris herrerana, Bathysa veraguensis, Ceiba rosea, Daphnopsis ameri- 
cana, Diospyros hartmanniana, D. panamensis, Freziera candicans, Gordonia fruticosa, 
Hedyosmum brenesii, Hillia loranthoides, Ladenbergia sericophylla, Oreomunnea pte- 
rocarpa, Quercus spp., Satyria warszewiczii, Saurauia montana, Symplococarpon pur- 
pusii, and Ticodendron incognitum. Some of these, such as Anthurium hoffmannii, 
Diospyros hartmanniana, D. panamensis, Hedyosmum brenesii, and Oreomunnea pte- 
rocarpa, have been found at even lower elevations (0O—300 m). 
The coastal vegetation of the Osa Peninsula is composed to a certain degree of spe- 
cies from drier, more seasonal habitats, such as Amphitecna latifolia, Anacardium ex- 
celsum, Aspidosperma megalocarpon, A. rigidum, Barnebydendron riedelii, Bernoullia 
