The species of rubber tree found at La Selva Biological Station is characterized by a conical stipule covering the apical bud, a milky latex, smooth bark and tiny clusters of flowers. There are three species of Castilla . These trees are characterized by bark with narrow, horizontal, reddish, raised pustules and white latex. The leaves are hairy, finely serrate, and oblong. The twigs are also hairy.
Fruits are orange and pulpy with numerous seeds inside.
Fruiting trees often are the center of activity of numerous forms of frugivorous wildlife. C. elastica trees were examined in a secondary forest section adjacent to the Bike Trail and behind the lawns of the research buildings on the grounds at La Selva. Observations consisted of three phases 1. All organisms visiting the trees and feeding on or moving fruits were recorded along with the time spent at the tree and brief notes of their activities. Additionally, observations were made regarding the passing of organisms feeding on the tree.