Bursera simaruba (L.) Sarg.
Burseraceae INDIO DESNUDO, GUMBO LIMBO
Tree: Occasional deciduous understory or subcanopy tree (15-25 m) found as a component of secondary forests or on extremely xeric (dry) sites. Indio Desnudo is most notable for its hardiness, its bronze-colored, pealing bark and its widespread use in rural areas as a “living fence post”.
Description: Indio Desnudo has a cylindrical and curving (never very straight or vertical) trunk (60 cm). Frequently the main bole subdivides early into secondary trunks that support many, upwardly-angled branches. The crown they form is moderately thick. The tree’s outer bark is characteristically smooth, bronze or reddish-brown in color, and has the texture of dry onion skin. It peals off in tattered, tissue-thin sheets, revealing inner bark that is contrastingly glossy green and waxy. Depending upon how much of the old bark is found adhering to them, Indio Desnudo boles vary dramatically in color between these two extremes. When bronze, they contrast strongly with the trunks of other forest trees (this is especially true in Guanacaste, where Indio Desnudo is a integral component of the region’s dry tropical forest). Most parts of the tree are impregnated with large amounts of transparent, sticky and pungently odorous resin. Leaves are alternate, imparipinnately compound, and about 25 cm long. Each glossy green leaf is made up of 7 or so leaflets that are elliptical in shape and possess prominent drip tips. Indio foliage senesces and falls during November and December, but only after first turning bright yellow and causing the trees to stand out from the surrounding vegetation. By January, they are leafless and they remain that way during the heart of the dry season. In April, new, pale green leaves are produced – in apparent anticipation of the rains that will not resume again until May.
Indio flowers are imperfect and the different sexes are found on separate trees – making this a dioecious species. Male (4 mm) flowers have five greenish white petals and five yellow stamens while the female variety sports only three petals, a central pistil with a large, rounded ovary, and several remnant, vestigial stamens. Both types of flowers are borne in axillary panicles from leaf scars after the foliage has been shed and last from mid-March through April.
Fruits appear immediately thereafter on female trees and they grow rapidly. By the time new leaf growth begins in April, they are already full sized and clearly visible – arranged in clusters on the branches behind the fresh foliage. Development then stops and the fruits remain static – apparently dormant – for nearly a year before finally maturing. Each is a three-sided, angular capsule that measures about 1 cm in diameter. When ripe, the capsules shed their three-part outer covering and reveal pale seeds surrounded by bright reddish-pink arils. Suspended from the open pod by a tiny thread, these fruits are then highly visible to potentially seed-dispersing birds. Fruiting occurs from February through April.
Similar Species: Green-barked tree species are rare but they include Barrigón (Pseudobombax septenatum), Palo Verde (Bombacopsis sessilis), and young Ceibas (Ceiba pentandra). Indio Desnudo is the only representative of this small group with pealing layers of red-brown bark to boot.
Natural History: Indio Desnudo is adapted to dry conditions and, in a relatively wet park like Manuel Antonio, it is largely confined to zones where geographical circumstances re-create dry tropical forest conditions (like those found in Guanacaste, where this tree ubiquitous). Steep, south-facing slopes draw maximal amounts of sunlight and can maintain only thin layers of soil (most being lost to erosion by rain and landslides). Unable to retain much water, they are therefore subject to rapid desiccation and extreme dryness. In Manuel Antonio, the most common tree found growing on such slopes is the hardy Indio Desnudo.
The smooth, waxy, slippery bark of this species combined with its tendency to peel off in papery sheets are probably an adaptation designed to rid the tree of shade and weight-producing epiphytes and climbing vines. In my own observation of one particular tree over a series of years, I have seen an orchid be shed from the tree trunk as it failed to gain a foothold on the tree’s slick surface.
Whether it occurs in temperate latitudes or in the tropics, deciduousness is an adaptation to dry conditions. Leaves cause plants to lose water through transpiration and evaporation and a leafless tree can cut down considerably on this loss. (In northern winters, the need is the same since, once frozen, soil water is unavailable to plants). Indio Desnudo can continue to produce food via photosynthesis even in this leafless state by virtue of the chlorophyll that keeps its bark green – a characteristic shared with the similarly dry-adapted Pseudobombax septenatum. Finally, the waxy layer that covers the bark and that gives it a glossy sheen helps make the bole impermeable – further locking in moisture and shielding against desiccation.
Pollination of Indio Desnudo flowers is by insects (they are visited by stingless bees of the Trigona and Hypotrigona genera, flies, ants, and beetles). Seed dispersal is carried out by color-sighted birds that are attracted to the bright-red arils of Indio fruits, as well as by white-faced monkeys, and squirrels (Stevens, 1983).
Stevens also reports that the smooth bark surfaces of Indio trunks are prefered by Synoeca wasps as nest-building sites. These large, black insects are known for their long, papery, tan-colored hives. (One such nest can be seen on the trunk of the tree in the photo at the top of this page.)
Uses: Indio Desnudo trees are commonly employed as “living fence posts”. The species is one of a very few whose severed branches are capable of sprouting roots and shoots and growing into new trees. In this process, short sections (1 m or so in length) of thin limbs are pruned from mature trees, cut at both ends, and then planted in the soil along the perimeter of a pasture. As they grow, their trunks surround and envelope the barbed wire that is attached to them, holding it fast. By pruning the trees annually, farmers keep them short and nearly crownless, though their boles still grow and fatten. In this way, they maintain a set of fence posts that may continue living indefinitely – eliminating the need for frequent post replacement and repair work. Other trees that are employed in this manner are Madero Negro (Gliricidia sepium), Jocote (Spondias purpurea), and Poro (Erythrina sp.).
Indio Desnudo’s wood is light and not of high quality. It has been used for making plywood, boxes, moldings and matches. The clear, sticky sap is used in making varnish, glue, and traditional medicine (including a weight-loss tonic) (Witsberger, 1982).
Distribution: In Manuel Antonio, Indio Desnudo can be found on the steep slopes and cliffs of Punta Catedral, Puerto Escondido, and Punta Serrucho. In a few places, isolated trees are found in the forest as well. In Costa Rica, it is most abundant and widespread in Guanacaste but can be found at low elevations all over the country. It ranges from California and Florida to Argentina (Stevens, 1983).
Photos: Tree Tree2 Tree3 Trunk Bark Leaf Flower Female Flower Male Flower Fruit
Trees of Costa Rica's Pacific Slope 
