Flora of Barro Colorado Island

Acacia melanoceras

Beurl., Kongl. Svenska Vetenskap­sakad. Handl. 1854:123. 1856

Shrub or small tree, to 6 m tall; branchlets and rachis puberulent, otherwise glabrous; branchlets armed with large spines, the spines 3-4.5 cm long, hornlike, paired, hollow, black, stipular. Leaves bipinnate with 15-26 pairs of pinnae; petioles 1-3 cm long, with several raised glands on upper side near base; rachis      12-25 cm long, usually with a single raised gland between pairs of pinnae; leaflets in 15-30 pairs per pinna, oblong, rounded to obtuse at apex, truncate and inequilateral at base, to 7 mm long, 1-2 mm wide. Inflorescences terminal, raceme-like group­ings of pedunculate heads; peduncles short, subtended by a 3- or 4-parted involucre; heads globular, densely flowered; floral bracts peltate, ± equaling flowers; flowers minute, yellow; calyx cupulate, ca 1 mm long, obscurely lobed; corolla funnelform, somewhat longer than calyx, puberulent apically; stamens numerous, 2-3 mm long. Legumes linear-oblong, to 11 cm long and 1.5 cm wide, ± compressed-subterete, short-beaked, longitudinally striate, glabrous, tardily dehiscent. Croat 6667.

Occasional, in the forest, especially on the west side of the island. Seasonal behavior uncertain. Probably flowering in February and March. Mature fruits have been seen in May.

Stipular spines often house ants that bite fiercely and remove any vegetation contacting the plant. The plant rewards the ants with sugars from the petiolar glands and with protein from the small beltian bodies along the margins of the leaflets (Janzen, 1967a). According to D. Janzen (pers. comm.), seeds merely spill out of the pods at maturity but may be dispersed further from the ground. Unless later regurgitated, seeds would probably not sur­vive the passage through a bird.

Costa Rica and Panama. In Panama, known from tropical moist forest in the Canal Zone and from tropical wet forest in Colón (Portobelo).

Photos from STRI Digital Archive

  • Acacia melanoceras Leaf
  • Acacia melanoceras Fruit
  • Acacia melanoceras Fruit
  • Acacia melanoceras Gland
  • Acacia melanoceras Fruit Leaf
  • Acacia melanoceras Fruit Leaf