Pithecellobium Saman (Jacq.) Benth. Monkey-Pod Leguminosae Legume Family
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Pithecellobium saman (Jacq.) Benth. Monkey-Pod Leguminosae Legume family Roger G. Skolmen Monkey-pod (Pithecellobium saman), saman in naturalized in Hawaii, Puerto Rico, and the Virgin Spanish, is a fast-growing tree that has been intro- Islands (3,10). The tree was reportedly introduced duced to many tropical countries throughout the into Hawaii in 1847, when Peter A. Brinsmade, a world from its native habitats in Central America businessman visiting Europe, returned to Hawaii, and northern South America. Although generally presumably via Panama, with two seeds, both of planted as a shade tree and ornamental, it has been which germinated. One of the seedlings was planted naturalized in many countries and is greatly valued in downtown Honolulu, the other at Koloa on the in pastures as shade for cattle. Short-boled, with a island of Kauai. These seedlings are possibly the spreading crown when open grown, it forms a long, progenitors of all the monkey-pod trees now in relatively straight stem when closely spaced. Its Hawaii (1). Monkey-pod may have been introduced wood is highly valued in some locations for carvings into Puerto Rico and Guam as early as the 16th and furniture (7). century. The most widely used common name for the species is raintree, from the belief that the tree Climate produces rain at night. The leaflets close up at night or when under heavy cloud cover, allowing rain to Monkey-pod grows in a broad annual rainfall pass easily through the crown. This trait may con- range of 640 to 3810 mm (25 to 150 in). On wet sites tribute to the frequently observed fact that grass (1270 mm 150 in] or more), its growth is often rapid. remains green under the trees in times of drought. This rapid growth is at times objectionable because However, the shading effect of the crown, the addi- the tree forms a large mat of surface roots and the tion of nitrogen to the soil by decomposition of litter crown becomes top heavy, thereby overbalancing the from this leguminous tree, and possibly, the sticky tree (5). In Hawaii, the climate in locations where the droppings of cicada insects in the trees all contribute tree is naturalized and spreading rapidly has winter to this phenomenon (3). The Hawaiian common maximum rainfall ranging from 1140 to 2030 mm (45 name, monkey-pod, is used here because it is a logi- to 80 in>, with a temperature range of 10” to 30” C cal derivation of the scientific name Pithecellobium (50” to 86” F). These climatic conditions are found (monkey earring in Greek). Besides monkey-pod, between elevations of 15 to 245 m (50 to 800 ft) at raintree, and saman, which is its name throughout several sites on three islands. Elsewhere, the tree is Latin America, the tree is called mimosa in the reported to grow at elevations of 0 to 700 m (0 to Philippines. 2,300 ft) (15). It is, however, very intolerant of frost and also, if grown near the shore, of windblown Habitat saltwater spray. Native Range Soils and Topography Monkey-pod is native from the Yucatan Peninsula Monkey-pod attains its best growth on deep al- in Mexico, through Guatemala to Peru, Bolivia, and luvial soils that are well drained and neutral to Brazil (3). It grows naturally in latitudes from 5” S. slightly acid in reaction. In Hawaii, most areas to to 11” N. (13). Cultivated throughout the tropics as which monkey-pod is well adapted are used for cul- a shade tree, it has been found in Burma, Ceylon, tivated crops. It has naturalized, however, on gently India, Jamaica, Nigeria, Sabah, Trinidad, Uganda, to steeply sloping Oxisols and Inceptisols on certain and the island of Zanzibar (12). The species is sites. On these sites it is most common in gullies naturalized in most of these countries as well as in where the soil is deeper and more moist than on the Philippines and Fiji (7). adjacent hills and ridges. It can, however, grow well In the United States and its possessions, monkey- on a wide variety of soils when planted and can pod grows in Hawaii, Florida, Puerto Rico, the Virgin withstand seasonal flooding (15). Islands, Guam, and the Northern Marianas. It is Associated Forest Cover The author is Principal Silviculturist (retired), Pacific Southwest Monkey-pod is frequently found on old home sites Forest and Range Experiment Station, Berkeley, CA. near streams in the forests of Hawaii where it is 507 Pithecellobium saman usually associated with mango (Mangifera indica), ti root planting. Nursery seedlings are of plantable size (Cordyline terminalis), guava (Psidium guajava), and in about 4 months (15). other escaped domestic plants. Where naturalized, it Seedlings grow rapidly if maintained, reaching 2 is associated primarily with grasses, although oc- to 3 m (6 to 10 ft) within 1 year after planting. casionally with such trees or shrubs as koa-haole Natural seedlings, or planted seedlings that are not (Leucaena leucocephala), Java-plum (Eugenia weeded, are strongly inhibited by competition and cumini), and Christmas-berry (Schinus terebin- grow much more slowly. Seedlings and mature trees thifolius). are intolerant of shade (15) and extremely suscep- tible to damage by overspray of herbicides used in weed control. Life History Vegetative Reproduction-Monkey-pod roots Reproduction and Early Growth easily. Hardwood (leafless) cuttings, ranging in size from 1 by 15 cm (0.4 by 6 in) to stems and branches of mature trees, can be rooted in moist soil on a site Flowering and Fruiting-Monkey-pod may without use of mist or shade. In Honolulu, it is com- flower at any time of the year in Hawaii, but it mon practice to transplant huge trees by cutting usually flowers from April to August, with the peak away almost all the roots and all the branches. Trees of flowering in May. The flowers are perfect and form grown at close spacing in the forest frequently have in umbels. The clusters, with their numerous pink branch-free stems 4 to 5 m (13 to 16 ft) tall and are stamens, 3.8 cm (1.5 in) long, look like powderpuffs transplanted to parking lots and parks as “instant” in the tree crown. The flowers are insect pollinated. full-size shade trees. Despite the ease with which it Seed pods develop in from 6 to 8 months and fall to the ground intact, usually between December and April in Hawaii. The dark brown and relatively straight pods are usually 15 to 20 cm (6 to 8 in) long and contain from 5 to 20 seeds (3,s). Seed Production and Dissemination-Seeds are reddish-brown beans about 13 mm (0.5 in> long that drop from the pods when they open on the ground. Although the seeds are hard coated and long lived, some germinate soon after moistening by soil contact, resulting in a short period of prolific reproduction even under lawn and garden trees, Most or all of the reproduction dies or is destroyed by insects, rodents, and lawn mowing. Seeds are easily collected by gathering pods on the ground and drying them under cover until they open. Natural dissemination is by birds and rodents. Seeds number from 4,400 to 7,OOO/kg (2,000 to Figure l-Monkey-pod shade tree at Moanalua Gardens, Honolulu, showing large, rounded crown, typical of open-grown (15). 3,20O/lb) They can be stored dry at 0” to 3” C trees of this species. (32” to 38” F) in closed containers for lengthy periods with little loss of viability. Seeds are normally scarified; they are placed in water at 100” C (212” can be vegetatively propagated, monkey-pod is al- F), then allowed to cool overnight. Scarified seeds most always started from seed. usually germinate 3 to 4 days after sowing. Sapling and Pole Stages to Maturity Seedling Development-Germination is epigeal. Seedlings are usually grown from seed planted in Growth and Yield-One of the best known trees containers. In Hawaii, polyethylene bags are now the of this species is in Trinidad. When a little more than most commonly used containers for this purpose. 100 years old, this tree had a trunk 244 cm (96 in) Monkey-pod seedlings have also been grown in seed in diameter, was (reportedly) 44.8 m (147 ft) tall, and beds and successfully planted bare-root in Hawaii, had a crown spread of 57 m (187 ft) (3). The large, but not on a large scale. Severe drought stress usual- rounded crown of open-grown trees (fig. 1) provides ly results in high seedling mortality following bare- shade over a wide area. Huge trees such as these are 508 Pithecellobium saman extremely dificult to log, so young, smaller trees are Stressed trees, however, are sometimes attacked by sought after for utilization, particularly those that the monkeypod roundheaded borer (Xystrocera are forest-grown and have long boles. globosa), which makes large galleries in the sapwood Although primarily a shade tree, monkey-pod also (11). In Puerto Rico, ants (Myrmelachista has potential as a timber tree. After the first year of ramulorum) bore into branchlets, resulting in planting at close spacings in Western Samoa, defoliation and leaf deformation (14). The defoliators monkey-pod averaged 4 cm (1.6 in) d.b.h. and 4.4 m can be controlled with insecticides applied to the tree (14 ft) tall (2). Because of its large crown, however, trunks (13). The tree is highly susceptible to leaf it requires wide spacing in plantations. A spacing of damage from herbicide overspray. Leaves are also 2.4 by 2.4 m (8 by 8 ft) proved much too close in very susceptible to damage by salt-laden mist from Zanzibar (12).