Cynometra hemitomophylla (Donn. Sm.) Britt. & Rose
Caesalpiniaceae GUAPINOL NEGRO
Tree: Common evergreen canopy (25-35m) tree found growing on well drained hillsides and valleys as well as along the sandy coastline. This species dramatically illustrates the unique and irreplaceable nature of the resources protected by Costa Rica’s National Parks because it is endemic to the country and it is found in greatest abundance within the 690 hectares that make up this tiny reserve. Guapinol Negro is a tree of great esthetic beauty thanks to its dense, emerald-green crown; towering, columnar trunk; and intricate, wavy buttresses. This tree usually grows in association with other individuals of its species, forming small stands.
Description: Guapinol Negro has a cylindrical, straight trunk (to 1 m) that gradually divides into a myriad of successively smaller branches and fine twigs. The twigs support a dense population of leaves, both inside and on the outer fringes of the canopy, producing a thick, impenetrable, and rounded crown. The lower two meters of the bole are dominated by long, thin, buttresses that disappear into the ground after subdividing and snaking around the base of the tree. Guapinol bark is smooth, gray-brown in color, and slightly exfoliating. Large quantities of multicolored lichens further mottle the bark with unexpected colors and patterns.
Guapinol Negro leaves are pinnately compound and alternately arranged along a distinctly zigzag twig. Each emerald green leaf is composed of a single pair of (almost sessile) asymmetrical leaflets that are mirror images of each other. (Although leaflet midribs are straight, there is more blade tissue on the inner sides of the ribs of each leaflet pair than on the outsides, producing the noted asymmetry. This easily recognizable pattern is shared by few other tall trees – Hymenaea courbaril and Peltogyne purpurea being among them). Basically elliptical in shape, leaflets (9 cm by 2.5 cm) end in pronounced, long-tapering drip tips. New Guapinol foliage – characteristically white to pale green and limp – appears first in July and sporadically thereafter until December.
Flowers (1.5 cm) are white with a prominent and flattened pink pistil, five petals, and eight long stamens. Smelling aromatically of the tropical Manzana de Agua fruit, they occur in short axillary racemes. The annual flowering season is short and occurs for about one week during July. Very often, trees limit their flowering activity to specific limbs – the majority of the tree remaining sterile. On rare, impressive occasions, the event is well choreographed and blossoms envelope the crowns of all trees simultaneously, creating a short-lived, but highly synchronized display. Under such circumstances, a continuous rain of fine flower petals fills the air and eventually blankets the ground.
Fruits begin to expand immediately after the flowers die, growing from the flat, pink ovaries. They mature as reddish brown, woody pods roughly 4 cm long by 3 cm wide. Each contains a single large seed that occupies its entire volume – leaving no room for an aril or other edible contents. The harvest is delayed until March of the following year, when pods finally begin to fall from the trees. This slow process then continues through May. The large seeds germinate within about a month of fruition, provided moisture levels are adequate.
Similar Species: Guapinol Blanco (Hymenaea courbaril) has leaves that share the same form as those of Guapinol Negro. In general, Hymenaea has much larger foliage (about twice the size of Cynometra‘s), and its leaflets are rounder and have less pronounced drip tips. Hymenaea is also usually a much taller tree (40 m or more), sporting an immense, cylindrical, and columnar bole.
Related Species: According to the Costa Rican botanist Quirico Jimenez, a second species of Cynometra exists in Manuel Antonio. Named C. retusa, it differs from C. hemitomophylla in having larger leaves (13 cm by 4 cm) with minutely cleft (indented) drip tips. Other differences between the two species are lacking and it has proven to be extremely difficult to distinguish them in the field.
Natural History: Cynometra flowers are visited by a wide variety of insects, including bees and butterflies. Leaf-cutter ants use the flowers for their fungus farms, sometimes traveling far up and down the boles of trees to harvest them. Mysteriously, Guapinol Negro fruits do not appear to have any effective means of dispersal (they lack any structures that could otherwise be construed as edible tissues, wings, barbs, etc.). It is possible that these woody pods are transported by water: Cynometra trees are often situated near streams and the buoyant pods could float to new locations downstream. Indeed, ocean dispersal could also help to explain this tree’s extreme abundance along Manuel Antonio’s sandy coastline. Nevertheless, water dispersal fails to account for Cynometra‘s presence in the dry, forest interior.
Brown-hooded parrots eat immature Guapinol Negro fruits, often destroying large numbers of the growing seeds. The fresh, limp foliage of this species is a popular food item as well, with Howler monkeys consuming large numbers of them. On occasion, immense populations of caterpillars appear – timing their arrival to coincide with well synchronized periods of new-leaf production. So many of these insects may be present, that the forest continuously crackles with the rain of their droppings.
Guapinol Negro is one of the few tree species capable of tolerating the doughtiness and high salt concentrations that typify the coastal environment. Though many individuals have succumbed in recent years to storms, the vegetated fringe behind the Third Beach is still dominated by Cynometra.
Uses: Guapinol Negro wood is dense and very hard. Older branches and trunks sport rich, black heartwood (hence the tree’s common name). This wood was once used in making ship keels, taking advantage of its great weight and resistance to the elements. Thanks to Guapinol’s thick, green crown and esthetic form, it would make an excellent ornamental and shade tree.
Distribution: In MANP, Guapinol Negro is found in all primary forest habitats. The species is endemic to Costa Rica, where it is found along the southern sections of both coasts. It is protected by Corcovado and Manuel Antonio national parks.
Trees of Costa Rica's Pacific Slope 
