Habit: Macroptilium atropurpureum is an annual that grows prostrate or climbing over other vegetation, is up to 1 m in height with stems covered in short soft hairs. The leaves are arranged alternately with stipules at the petiole base. The leaves are compound with 3 leaflets that are orbicular to rhombate, an acute leaflet apex and entire (or with an outer lobe) margin. The leaves are often covered with hairs.
The complete, perfect, zygomorphic flowers, on short pedicels, are arranged in racemes that can be up to 30 cm in length. The calyx has 5 fused, pubescent, sepals that are greenish and form a short tube. The corolla has 5 dark purple to black petals that are fused at their base. There are 2 petals forming a keel and a single large petal that is the standard. There are 10 stamens with 9 of them fused forming a partial tube around the ovary. The ovary is superior with a single locule. Around the base of the ovary is a short nectary. The fruit is an elongate linear legume. The fruit twists as it matures and is elastically dehiscent.
Habitat: Macroptilium atropurpureum is considered a weedy species growing in Human Altered environments (old fields, roadsides, and abandoned farms).
Distribution: Macroptilium atropurpureum is NOT native to the Lucayan Archipelago. It is native to Central and northern South America. It now grows in the southern United States, eastern South America, and tropical and subtropical regions of the world.
Medicinal/Cultural/Economic usage: Macroptilium atropurpureum has been used in the Lucayan Archipelago to treat jaundice.
Macroptilium atropurpureum has been used as a forage species in some areas. It is also a known nitrogen fixer and thus has been useful for soil amendment.
It is considered a NON-NATIVE INVASIVE in many countries.