Manual de Plantas de Costa Rica 189 
flammea, Bombacopsis sessilis, Brassavola nodosa, Brosimum alicastrum, Cnestidium 
rufescens, Copaifera camibar, Cuervea kappleriana, Cydista aequinoctialis, Cyno- 
metra bauhiniifolia, C. hemitomophylla, Erblichia odorata, Inga vera, Lafoensia puni- 
cifolia, Licania arborea, L. operculipetala, Myroxylon balsamum, Paramachaerium 
gruberi, Piper friedrichsthalii, P. guanacostense, Pithecellobium hymenaeifolium, 
Platymiscium curuense, Pouteria foveolata, P. triplarifolia, Prestonia mexicana, P. tri- 
fida, Pseudobombax septenatum, Psychotria acuminata, P. carthagenensis, P. nervosa, 
P. pubescens, Simaba cedron, Talipariti tiliaceum, Trigonia rugosa, Triplaris melaen- 
odendron, and Ximenia americana. The majority of these species are found all along 
the coast from Carara National Park to the Burica Peninsula. 
Within these forests of generally high diversity, there exist pockets with special fea- 
tures and very low diversity, such as the mangroves (e.g., at the mouth of the Rio 
Rincoén, Puerto Jiménez, and the Rio Sirena), with the species associations already 
mentioned; Chocuaco and Corcovado Lagoons, dominated by such species as Raphia 
taedigera, Bactris major, Elaeis oleifera, Mora oleifera, and Pterocarpus officinalis; 
and swamp forests (at the mouths of the large rivers of the area), dominated by the as- 
sociation Mora oleifera-Pterocarpus officinalis, or P. officinalis alone with Crinum 
erubescens in the understory. Janzen (1978) called these associations “monocultures,” 
because of the high density of so few species. 
It is worth mentioning that, near Playa Piro at the southern end of the peninsula, a 
small patch of the Curatella americana-Byrsonima crassifolia association is found, in 
combination with a number of elements from dry savanna woodlands such as Cnestid- 
ium rufescens, Corchorus siliquosus, Miconia argentea, Palicourea triphylla, Rourea 
glabra, Tetracera hydrophila, and Xylopia frutescens. This isolated patch is relevant to 
the conclusions of Prado and Gibbs (cited by Pennington et al., 2000), which suggest 
that these fragmented distributions might be remnants of a once continuous area that 
perhaps reached its maximum extent during the dry/cold period of approximately 
18,000—12,000 B.C. 
Origin of the flora 
Costa Rica and Panama comprise Isthmian Central America, the site of a marine portal 
that isolated South America and Central America until at least 15 million years ago 
(middle Miocene). The present land surface consists of thick marine sediments and vol- 
canic rocks, deposited during the late Cretaceous and Tertiary over an oceanic crust dat- 
ing mainly from the Jurassic to middle Cretaceous (Weyl, 1980). During the middle and 
late Miocene (ca. 15—6 million years ago), Costa Rica was represented by archipelagoes 
of varying configuration, part of the Caribbean tectonic plate. Closure of the isthmus, 
initiated by the collision of the westerly Cocos plate with the Caribbean, involved the vi- 
olent uplift of the axial cordillera, still ongoing. The peninsulas of Santa Elena (but see 
