Ant acacia

Vachellia allenii is a tree with widely spreading branches, that can grow up to 22 metres (72 ft) high. The species is resistant to light ground fires. The bark is green to light brown, and rough. The leaves are compound, very dark green, and 20–40 centimetres (7.9–15.7 in) long. Each leaf has up to forty segments, which are 7–10 centimetres (2.8–3.9 in) long. The leaves have beltian bodies. The inflorescences are globular, up to 5 millimetres (0.20 in) long and wide, and grow on 3–7 millimetres (0.12–0.28 in) stems.

Vachellia allenii lives for around twenty-five years, and first produces seeds at around seven years. The seed pods are dehiscent, and greenish-black when mature. The seeds are black. Vachellia allenii is a myrmecophyte, symbiotic with stinging ants. Ant species such as Pseudomyrmex ferruginea and Pseudomyrmex particeps live in the tree, though the tree will support other species if they are artificially introduced. The ants protect the tree from herbivores. Vachellia allenii is part of the swollen-thorn Vachellia group. It has thorns up to 4 centimetres (1.6 in) long. The thorns of trees occupied by ants are dark brown or black in colour. V. allenii is similar to Vachellia melanoceras, and the species are likely to be closely related. The species differ in their geographic range, and the details of their foliage and thorns. …

Vachellia allenii is native to the wet tropical biome of Puntarenas, Costa Rica. It is endemic to the south-west of the country, and is mainly present in Osa Peninsula and Golfito. The species grows in primary, secondary, riparian lowland, and disturbed forests, at elevations of up to 800 metres (2,600 ft).