Hymenaea courbaril L.
GUAPINOL, STINKING TOE
Tree: Common emergent evergreen tree (40 m) of immense proportions found in all of Manuel Antonio’s primary forest habitats. Guapinol appears to prefer the well drained soils usually associated with slopes, hillsides, and ridges and its distribution is fairly uniform where these conditions are present. This tree is native to much of Costa Rica’s humid, Pacific lowland forest, however rarely does it achieve the huge circumferences and staggering heights that are observed in Manuel Antonio, where it ranks among the top two or three tallest species. Guapinol is an interesting and readily identifiable tree, thanks to its large, edible pods, distinctive leaves, and emergent growth form.
Description: Guapinol trees have perfectly cylindrical and straight, columnar trunks that often measure far in excess of one meter in diameter. Rising from the wide base where low, rounded, root-like buttresses anchor it to the soil, the towering bole continues, unbranched, well past the forest canopy. There, stout and often horizontal limbs spread out widely, creating a hemispherical, umbrella-shaped crown of moderate to thin density. Guapinol bark is smooth and gray (though often mottled by a variety of multicolored lichens), with finely textured vertical cracking evident upon close inspection. At times, accumulations of the tree’s thick, clear-yellow, resinous sap are visible around breaks in the bark.
Guapinol’s trademark leaves (11 cm by 10 cm) are pinnately compound, alternate, and composed of two, paired asymmetrical leaflets on a 1.5 cm petiole. Very thick, smooth and waxy, they have the feel of stiff leather. Each leaflet in the pair – one the mirror image of the other – is basically elliptical in shape, though slightly falcate (each curving toward the other) and ending in a blunt point. Leaves slowly begin to senesce, yellow, and fall in September and by the end of October, the trees are generally bare. In November, as large, fleshy stipules are shed, a growth spurt culminates in the establishment of a fresh, light-green and thick leaf cover.
Flowers, representing the final stage in this growth cycle, appear in thick terminal and sub-terminal racemes on the new twigs. Each blossom (5 cm) has five bicolored (rust and green) velvety sepals; five large, white petals; ten long, protruding stamens; and a single central pistil with a wide, flat, angular ovary. Flowering lasts from late December through mid-February, though individual trees are fertile for only about one month.
Fruits grow rapidly from the flattened, angular ovaries and reach full size within about six months. However, they remain in the canopies a full 14 months before harvest commences. Fruits mature as large (15 cm by 8 cm by 5 cm), reddish-brown, somewhat lobed pods (only slightly resembling a human toe). Inside the indehiscent pod’s thick and woody outer wall, three or four black, ovoid seeds (3 cm) are surrounded by a dry, fibrous, tan-colored powder. Though unpleasant to smell, this filling is edible and sweet and has a date-like flavor. Fruit harvest begins, slowly, in late February and reaches full force in March and April. Seeds germinate immediately with the first rains of May and June, provided the thick seed coat has been scratched to allow hydration. New seedlings, 20 cm tall with pink stems and sporting a pair of disc-shaped leaves, are easily recognizable.
Similar Species: Cynometra hemitomophylla (Guapinol Negro – see description) has similarly shaped, paired, asymmetrical leaves. In general, they are smaller, more tapered and more pointed than those of Hymenaea. Also, the Cynometra tree itself is less massive – almost never reaching a meter in diameter and attaining only canopy height. Hymenaea lacks significant buttresses, while Cynometra nearly always sports well developed roots of this type.
Natural History: Pollination in Hymenaea is accomplished through the action of wasps and bees that can be observed buzzing around the flowers in large numbers during the day, and by nectar-seeking bats at night (Janzen, 1983). Though trees produce copious numbers of flower buds annually, the majority are often aborted while still in this stage – precluding the possibility of a large harvest. Individual Guapinol trees in Manuel Antonio National Park (MANP) never produce large fruit crops in consecutive years. Instead, heavy harvests are spaced over three to four year intervals. This behavior could be related to the high energy cost of such prolific fruit production – but it could also be a strategy designed to keep predatory insects off-balance by denying them a consistently abundant food source. Nonetheless, Guapinol fruits are heavily parasitized by weevils that enter the young pods, consume the seeds, and bore their way out of the mature pods as metamorphosed adults – leaving characteristic 6 mm holes the pod walls (Janzen, 1983).
Seed dispersal in Guapinol is something of an enigma. There appear to be no effective consumers of these tough pods and the vast majority remain unopened on the forest floor until they rot. New generations of seedlings then germinate at the base of the parent trees, where they have little chance of long-term survival. To be sure, Agoutis and Pacas (medium sized mammals of the Rodent family) manage to get a few pods open, but these are usually eaten in place with no dispersal occurring. Janzen and Martin (1982) have theorized that the dispersers of Guapinol seeds (as well as those of several other tree species) went extinct 10,000 years ago (at the end of the last ice age) when several species of large, ground-dwelling mammals (giant ground sloths, mammoths, giant bison) succumbed to a change in climate or perhaps even to human predation. Perhaps since that time these trees have survived without the aid of an effective disperser, possibly declining in numbers as a result.
In a good year, a Guapinol tree can fabricate enough fruits to nearly cover the ground beneath it. As indicated above, these pods are large and heavy. When they are released from high branches, they begin a long, 40 or 50 m fall to the forest floor, audibly crashing through the subcanopy vegetation that they encounter along the way. Using some simple physics, the pod’s velocity at impact can be found to be as high as 31 meters/second (112 km/h) – so lingering under shady, fruit bearing Guapinol trees during March and April is definitely not recommended!
Guapinol’s resinous, clear sap dries into a hard, rock-like but transparent material called amber. Amber produced by ancestral Guapinol trees has sometimes preserved prehistoric insects that became trapped in the sticky tree sap when it was fresh. A related but extinct Hymenaea species – known to have existed in the Caribbean – was the source for the large quantities of amber still being mined today (Morell, 1993).
The influence of environmental factors on tree physiology is particularly easy to see in this species. Native to Costa Rica’s Pacific slope, Guapinol trees thrive in areas with diverse rainfall regimes. Guanacaste (in the drier, north Pacific region) experiences as many as six consecutive months of dry weather annually, made worse by sustained, desiccating winds. Manuel Antonio (in the south-central Pacific area) sees a dry season scarcely half as long. Furthermore, the rainy season here is more consistently wetter than is that of Guanacaste. This difference in growing conditions is reflected in the physical characteristics of the populations of Guapinol trees present in both regions. Guanacaste Guapinols (like those present in Santa Rosa National Park) are typically shorter (20m), less straight, and possess leaflets that are two to three times smaller (5 cm) than those of Manuel Antonio. Climactic and edaphic conditions in Manuel Antonio must be close to ideal for this species, for it reaches superlative dimensions in every respect in this park – dimensions that are unrivaled by nearly any other Guapinol tree seen in Costa Rica. As an example, the large trailside tree in Punta Catedral measures a whopping 1.2 meters in unbuttressed, cylindrical diameter!. (One individual, known from the south-Pacific park of Corcovado – where this tree is not abundant and where humidity regimes are comparable to or exceed those in Manuel Antonio – matches the Manuel Antonio trees in height and girth.)
In El Salvador, Hymenaea is known as “Copinol” – a name derived from the indigenous Nahuatl language and meaning “Flour Tree” (Witsberger, 1982).
Uses: Guapinol has a fine, deep-reddish wood with a pronounced, linear grain. This wood is highly appreciated for its quality and hardness and it is used in artisanry and furniture-making. The foul-smelling, dry powder of the pods is eaten and it is pleasant tasting, though of a thick and pasty consistency (it is a bit like eating powdered milk). Beverages are sometimes made from this pulp. Finally, the sap has been employed in the production of varnishes and resins, as well as in traditional medicines (Witsberger, 1982).
Finally, Guapinol trees retain their leaves during the – often pronounced – dry season along Costa Rica’s Pacific slope – a time when many other trees shed their leaves to conserve water. They are thus in a position to provide much appreciated relief from the relentless and intense sunlight that bathes this region during the early months of the year. Guapinol trees thus possess enormous potential as shade trees in yards, parks, and along city streets. The photo above shows a hillside and valley covered with trees in in Santa Rosa National Park on one May 1st. Notice the stand of Guapinol trees – distinguishable from their deciduous neighbors by their persistent bright green crowns…
Above all, the Guapinol serves as a stately, ornamental tree – as a towering and monumental testament to the magnificence of nature.
Distribution: Guapinol ranges from Mexico to Peru, Bolivia, Brazil and the Antillies. In Costa Rica, it is found along the Pacific coastal plane. dry to humid sections of the Pacific Coast, and in some sections of the Central Valley (Ciudad Colon), but perhaps nowhere so dominantly as in Manuel Antonio.
Trees of Costa Rica's Pacific Slope 
