About Mimosa pigra var. asperata (L.) Zarucchi, Vincent & Gandhi
Mimosa pigra is a leguminous shrub that can grow up to 6 meters tall. Young plants have greenish stems that become woody as the plant matures. Stems are covered in broad-based prickles up to 7 mm long. Its leaves are bright green and bipinnate, made up of a central prickly rachis 20 to 25 cm long, with up to 16 pairs of 5 cm-long pinnae. Each pinna is further divided into pairs of leaflets 3 to 8 mm long. The leaves are sensitive: they fold up when touched and at nightfall. Its flowers are mauve or pink, arranged in tight, subglobose pedunculate heads 1 cm in diameter. Each head holds approximately 100 flowers. Each flower head produces a cluster of 10 to 20 seedpods. When the seedpods mature, they break into segments, each containing one oblong-shaped seed. Hairs on these segments allow them to float on water and stick to hair or clothing, which helps with seed dispersal. Ripe seeds range in color from light brown to brown or olive green. Mimosa pigra produces hard seeds; seeds can survive for at least 23 years on sandy soils, though seed viability decreases more quickly on clay soils. If soil is moist but not flooded, Mimosa pigra can germinate year-round. Most germination occurs at the start and end of the wet season. Seedlings grow rapidly, and flowering occurs between 4 and 12 months after germination. It takes about five weeks from flower bud development to produce ripe seed. Mimosa pigra is closely related to Mimosa pudica, the common sensitive plant. It can be told apart from Mimosa pudica by its larger overall size, longer seedpods (6 to 8 cm long, compared to 2.5 cm long for Mimosa pudica), and more pairs of pinnae on its leaves (6 to 16 pairs, compared to just 1 to 2 pairs on Mimosa pudica leaves). Mimosa pigra is native to tropical America, where it grows in a wide belt stretching from Mexico through Central America to Northern Argentina. Today it is widespread across the tropics, and is a serious weed in Africa, India, South-East Asia, Australia, and some Pacific Islands. In Cambodia, it is known by the common names ព្រះខ្លបយក្ស /prĕəh kʰlɑːp jĕəʔ/ “giant mimosa,” បន្លាយួន /bɑnlaː juən/ “Vietnamese thorn”, and បន្លាយក្ស /bɑnlaː jĕəʔ/ “giant’s thorn”. Mimosa pigra prefers wet, tropical climates. It does not show a strong preference for any single soil type, but it is most commonly found in moist areas such as floodplains and river banks. It grows in a range of soils from black cracking clays, through sandy clays, to coarse siliceous river sand.
