Manual de Plantas de Costa Rica 143 
such as swamp or inundated forests, reach their northwestern limit in the northern re- 
gion, here they are fully expressed, more common, and more extensive. Nevertheless, 
these swamp forests are basically the same as those of the Llanura de San Carlos, at 
least with regard to the canopy trees and the dominant species (see Hartshorn & Ham- 
mel, 1994; Webb & Peralta, 1998). The understory of these forests is nearly dominated 
by small palms, principally of the genera Asterogyne, Astrocaryum, Bactris, Calyp- 
trogyne, and Geonoma. 
Obviously, the effects of these soils with a very high water table are reflected in the 
composition of the flora. Studies of similar-sized areas (ca. 16 ha) and on individuals over 
10 cm DBH— site 1, in the northern part of the Llanura de San Carlos (N. Zamora V., 
unpubl. data), and site 2, toward the Llanura de Tortuguero (Webb & Peralta, 1998) — 
showed that, of the 10 families with the greatest number of species at each site, seven 
occur at both sites. Families such as Chrysobalanaceae, Melastomataceae, and Vochysi- 
aceae, found at site 1, tend to prefer well-drained soils on hilly terrain, while families 
such as Annonaceae, Burseraceae, and Flacourtiaceae, found at site 2, demonstrate a 
preference for poorly drained soils on flatter terrain. Refining the comparison down to 
the level of species, the differences between these two sites are more evident: of the 10 
most common or dominant species at each site, only one, Pentaclethra macroloba, is 
shared. This is a reflection of the differences in topography and drainage of the two sites. 
Near the boundary with the neighboring Llanura de San Carlos, certain species 
occur that are more or less unique to the subregion, e.g., Guatteria alata, Hirtella tri- 
chotoma, Inga ciliata, Licania stevensii, Macrolobium herrerae, Sipanea biflora, and 
Unonopsis stevensii. Of these, Hirtella trichotoma, Licania stevensii, Macrolobium 
herrerae, and Unonopsis stevensii are considered endemic, while others, such as Guat- 
teria alata and Sipanea biflora, are known in Costa Rica only from this area. 
Generally speaking, the mixed forests of this subregion are dominated by only a 
few tree species—1in numerous cases by Carapa guianensis, Pentaclethra macroloba, 
and Pterocarpus officinalis—that together can make up more than 70% of the base 
area (Webb & Peralta, 1998). Nevertheless, these same authors point out that, across 
the whole of the region, there is considerable heterogeneity. For example, more than 
half of the total 225 species tallied in the cited work were found at just one site. 
All along the Caribbean coast, the forests are dominated by large stands of impor- 
tant associations, such as the aforementioned yolillales, where Campnosperma pana- 
mense, Manicaria saccifera, and Raphia taedigera are abundant. In other forests, 
species such as Apeiba membranacea, Calophyllum brasiliense, Carapa guianensis, 
Ceiba pentandra, Dialium guianense, Elaeis oleifera, Ficus insipida, Grias cauliflora, 
Hernandia didymantha, Lonchocarpus cruentus, Luehea seemannii, Manilkara spec- 
tabilis, Pentaclethra macroloba, Prioria copaifera, Pterocarpus officinalis, Simira 
maxonii, Symphonia globulifera, Tabebuia rosea, Terminalia oblonga, and Virola 
koschnyi are abundant. Among understory palms other than Elaeis, Manicaria, and 
