Manual de Plantas de Costa Rica 157 
Mimosoideae), Poaceae, Cyperaceae, Bignoniaceae, Euphorbiaceae, Asteraceae, Con- 
volvulaceae, Malvaceae, Moraceae, Rubiaceae, and Solanaceae. Other families such as 
Acanthaceae, Apocynaceae, Boraginaceae, Capparaceae, Malpighiaceae, Polygona- 
ceae, Sapindaceae, Sterculiaceae, and Verbenaceae are conspicuous by virtue of their 
diversity of species. For some taxa, e.g., Bursera, Capparaceae, Convolvulaceae, Mal- 
vaceae, Polygonaceae, and Sterculiaceae, this is the part of the country in which they 
are most diverse. A corollary observation is that, in these dry forests, species diversity 
is noticeably low in families typically diverse in wetter forests, e.g., Araceae, Areca- 
ceae, Bromeliaceae, Elaeocarpaceae, Gesneriaceae, Heliconiaceae, Lauraceae, Melasto- 
mataceae, Myrsinaceae, Orchidaceae, Piperaceae, and ferns in general. 
Santa Elena Peninsula near Playa Potrero Grande (2000) 
This dry forest association extends toward the southeast, primarily below 400 m el- 
evation, although a few species, such as Quercus oleoides, range upward to ca. 900 m 
in the Cordillera de Guanacaste; others, including Echeveria australis, Euphorbia 
schlechtendalii, Furcraea cabuya, Maytenus segoviarum, Plumeria rubra, and Selagi- 
nella pallescens, ascend to 700—800 m in the Monteverde area (Haber, 2000a), and 
even higher elsewhere. 
Toward the west coast, many dry forest species encounter on the Nicoya Peninsula 
a sort of climatic barrier, since the rainfall there is greater, with an annual average of 
2000 mm (Herrera, 1985). Nevertheless, in the Rio Tempisque valley an orographic rain- 
shadow effect gives rise to other areas of dry forest, as, e.g., in Palo Verde National 
Park, Lomas Barbudal, and Cerros El Rosario. These forests occur mostly on limestone 
outcrops, which confer their own distinct character to the terrain. Some species tend to 
be especially common here, e.g., Aspidosperma megalocarpon, Bursera schlechten- 
dalii, Erythroxylum havanense, Euphorbia schlechtendalii, and Guaiacum sanctum, in 
some cases forming almost pure stands. Others, such as Opuntia lutea, Pitcairnia cal- 
