Description ลักษณะ
M. pigra is a spreading, multi-stemmed, thorny shrub usually up to 2 m tall, but occasionally up to 6 m, with a maximum lifespan of about 5 years.
The plant is evergreen and bears bipinnate, sensitive leaves, up to 18 cm in length. Recurved spines (to 7 mm long) are located on the undersides of the petioles, petioules and stems.
The inflorescences, containing up to 100 flowers, are spherical (about 1 cm across) and pink. The species is androdioecious with both male and hermaphrodite flowers bearing eight short and long stamens. These flowers exhibit an intra-specific pollen polymorphism (El Ghazali et al., 1997). The flat pods of M. pigra are hairy and up to 15 cm long and clustered (up to seven pods) at the stem tips. They contain between 8 and 24 seeds. Each seed is about 5 x 2.4 mm and weighs 0.09 mg. The fruits ripen in about 3 months and, when mature, fragment into indehiscent one-seeded segments. The pods are covered with bristles which facilitate floating and enhance dispersal along river systems.