Samanea saman (Jacq.) Merr.
Mimosaceae CENIZARO, RAINTREE
Rare canopy evergreen tree (20-30 m) more usually associated with the dry tropical forests typical of Costa Rica’s northwestern lowlands (e.g. Guanacaste). Nevertheless, a few prominent individuals can be found among the forests of the more humid, southern Pacific slope. This tree remains an outstanding species thanks to its massive stature, spreading crown, and high quality wood. It has been extensively planted outside the primary forest and thus can be found thriving all over Costa Rica.
Description: Cenizaro has a cylindrical but short and stout main trunk (>1m) that usually divides into secondary boles only a few meters above the ground. Angling away from the vertical, these rafter-like boles extend outward and upward for many meters, forming the framework for an extremely wide and spacious, hemispherical crown. Large individuals of this species appear to defy gravity as their hefty, often horizontal limbs amble away from the main trunk for unreasonably long distances. Foliage is confined to the outermost fringes of the twigs and the shell-like crown is therefore open, airy and thin. Cenizaro bark is gray-brown, characteristically rough, and deeply fissured by vertical cracking. Exfoliation occurs in stubby, irregular plates. Buttresses are absent.
Cenizaro leaves are large (35 by 23 cm), bipinnately compound and alternate. The lightly pubescent petiole supports four pairs of oppositely arranged leaflets with a small gland located between each pair. Leaflets are, in turn, composed of a variable number of asymmetrical, tomentose blades that range in number from four to twelve and that vary in size from 1.5 to 4 cm. Leaflet size (largely determined by blade number) increases with distance along the petiole. Similarly, blade size increases with distance along the leaflet. The entire, complex structure is remarkably planar when fully extended. All foliage is shed completely during the later part of February and is rapidly replaced by new vegetation in March.
Flowers emerge on axillar spikes as the new leaf coat matures. roughly spherical heads (8 cm) are loosely composed of about twenty tubular flowers and a long (5 cm) pedestal. Individual blossoms sport a small green calyx; a five-pointed, pink corolla; and a bundle of about twenty long (4 cm), pink stamens. It is these abundant and showy filaments that give the Cenizaro flower its most eye-catching characteristic. Splashes of delicate red and pink agreeably dapple the light green of the fresh foliage during the flowering season, which lasts from mid-March through mid-May.
Fruits remain invisible – or at least inconspicuous – for the following seven months. Finally, in late October, tiny shoelace-like green pods make an appearance high in the crown. By early December they have grown to full size (20 cm long by 2 cm wide), but remain green and persist in the canopy until February. Maturing as somewhat flattened, brown pods with narrow, encircling, whitish bands – they rapidly fall to the ground during this month, invariably accumulating underneath the parent tree. Inside each fruit, a sweet-smelling, honey-like resin surrounds a series of hard-coated, dull-brown, ovoid seeds (1 cm). Harvests are seldom annual events, with many trees following two-year or more infrequent fruiting cycles. Seeds show high viability and they germinate easily and rapidly – within a month of the beginning of the rainy season (usually in early May).
Similar Species: Cenizaro’s unique leaves are easy to recognize and they serve to positively identify this species. Only the Gavilan tree (Pseudosamanea guachapele) has similar leaves but this latter tree has much rougher, shaggy bark that is very different from that of a Cenizaro.
Natural History: Cenizaro flowers are pollinated by butterflies, bees, and other insects (and at night by moths – Janzen, 1983). Its fruits are eaten by few animals and apparently lack an effective means of seed dispersal. Though pacas and raccoons forage haltingly on the fallen pods (and horses and cattle love them), no native mammals eat them in the quantities presumably necessary to promote the effective transport of their seeds. Here, again, Janzen & Martin (1983) propose that the original vectors responsible for Cenizaro seed dispersal are now extinct – having succumbed with other large, Neotropical rainforest mammals some ten-thousand years ago (see description for Guapinol).
The English common name for this species, Raintree, derives from the drops of moisture that periodically fall from the Cenizaro crown. The excretions of certain sap-sucking arthropods (of the Homoptera genus) are given responsibility for this phenomenon (Janzen, 1983).
At dusk, or when the sky suddenly darkens before a late afternoon rainstorm, Cenizaro leaves exhibit an osmotically-controlled folding response (known as a nastic movement). Leaflets collapse and the blades drop to vertical positions and come close together. The planar nature of the leaves is broken and the canopy appearance changes dramatically. This response may be viewed as a behavioral adaptation that helps to protect the foliage during storms. A dry-adapted tree, this habit may also help Cenizaro conserve water at night by limiting the number of blade surfaces exposed to the desiccating air.
Uses: Cenizaro wood is among the most highly prized and widely appreciated timbers of the tropical forest. Very coarse grained and tan brown in color, it is marbled by rich veins of much darker wood. Depending upon the angle of illumination, different textures and grain patterns of the wood are accented.
Cenizaro, a member of the leguminous Mimosaceae family, is another tree capable of harboring nitrogen-fixing bacteria in its roots. Nitrogen, a necessary and often scarce nutrient, is returned to the soil in leaf litter and thus helps to enrich the edaphic environment.
Cenizaro seedlings germinate easily, grow rapidly, sport a handsome form. Seeds, collected and removed from the pods during the late dry season, will sprout immediately if the hard, waterproof, outer coat is nicked before sowing. They also may be stored in the refrigerator for many months without loosing viability.
Distribution: Cenizaro trees are most typically found amid the flora of Costa Rica’s dry tropical forests, like those still found in Guanacaste in parks like Santa Rosa and Palo Verde. Nevertheless, the species has been planted prolifically and it is commonly found in pastures even in Costa Rica’s wetter regions. Cenizaro ranges from Mexico northern South America.
Photos: Tree Trunk Trunk2 Leaf Flower Flower2 Fruit Seedling Seedling2
Trees of Costa Rica's Pacific Slope 
