Manual de Plantas de Costa Rica | The physical environment | 65 
In the Central Pacific region, several rivers flow from the western portion of the 
Central Valley and the southern slopes of the Cordillera Central. The most important of 
these are (from north to south) the Rio Barranca, Rio Jesus Maria, and Rio Grande de 
Tarcoles. Several well-known tributaries of the last-mentioned river cross the most 
heavily populated parts of the Central Valley, viz., the Rio Virilla, Rio Torres, Rio Tiribi 
(formerly Tilirf or Tiliri), and Rio Ocloro. It is worth noting that the Rio Tiribi is today 
considered an affluent of the Rio Virilla; however, the reverse was true in the time (or 
at least in the minds) of Pittier and Tonduz. The Rio Parrita (or Rio Pirris) enters the sea 
near the town of the same name, somewhat to the south of the Rio Grande de Tarcoles. 
Together with its major tributary, the Rio Grande de Candelaria, it drains the northern 
end of the Cordillera de Talamanca, a task shared by several other major rivers includ- 
ing the more southerly Rios Naranjo and Savegre. 
The most important river system in the southern Pacific region of Costa Rica is 
that of the Rio Grande de Térraba, known upstream as the Rio General and (still fur- 
ther) the Rio Chirrip6 Pacifico, which enters the sea west of Palmar Norte. With its 
tributaries (including the Rio Ceibo, Rio Coto Brus, and Rio Cotén), this system 
drains the western slope of most of the Cor- 
dillera de Talamanca (including the Fila 
Costefia), by way of the General and Coto 
Brus Valleys. Near the Panamanian border, 
a much smaller system centering on the Rio 
Coto Colorado (with its tributaries, includ- 
ing the Rio Colorado, Rio Corredor, and 
Rio Conte) empties into the eastern side of 
Golfo Dulce, carrying some waters from the 
southern Fila Costefia and the hills at the 
foot of the Burica Peninsula. 
The major hydrological feature of the 
Osa Peninsula is the extensive, marshy Cor- 
covado Lagoon, an important wetland and, 
along with Lago Cafio Negro, one of the 
largest bodies of freshwater in Costa Rica. 
The rather smaller Sierpe Lagoon, in swamp- 
lands to the north of Golfo Dulce, was im- 
mortalized by Pittier in both collections Rio Grande de Térraba (2000) 
and prose. 
Seasonal or vernal lagoons of various sizes are relatively frequent on the Pacific 
slope, especially in the Guanacaste region and in savanna and other xeric habitats south- 
ward. Some such sites are of considerable historical significance to Costa Rican floris- 
tics, such as the lagoons near Buenos Aires, in the General Valley, and at Cafias Gor- 
das, on the Panamanian border. 
