VietNamNet Bridge – Mai duong (mimosa pigra), listed among the 100 most invasive species in the world by the IUCN, is growing in 44h of land in 11 districts of HCM City.

Mimosa pigra.

The Chief of the HCM City Plant Protection Agency, Nguyen Van Duc Tien, said this tree is developing in the districts of 2, 9, 7, 12, Thu Duc, Nha Be, Can Gio, Binh Chanh, Cu Chi, Hoc Mon, and Binh Tay, totalling around 44ha of land.

The agency recently sent a report warning about the danger caused by the spread of mai duong to the HCM City Department of Agriculture and Rural Development. It is lucky that this tree has just been developing in unused areas, not cultivated land yet.

The local Department of Agriculture and Rural Development said it would carry out a survey about the encroachment of mai duong in the city and define areas where mai duong will be destroyed first.

Mimosa pigra is a leguminous shrub, which can reach up to 6m in height. The stem is greenish in young plants but becomes woody as the plant matures. It is armed with broad-based prickles up to 7mm long. The leaves are bright green and bipinnate, consisting of a central prickly rachis 20 to 25cm long with up to 16 pairs of pinnae 5cm long, each divided into pairs of leaflets 3 to 8 mm long. Leaves are sensitive and fold up when touched and at nightfall.

Flowers are mauve or pink, born in tight, subglobose pedunculate heads 1cm in diameter, each containing approximately 100 flowers. Each flower head produces a cluster of 10 to 20 seapods, which then mature and break into segments, each containing an oblong-shaped seed. Hairs on the segments allow them to float on water and stick to hair or clothing, hence aiding in dispersal.

Ripe seeds are light brown to brown or olive green. Mimosa is hard seeded. Seeds can survive at least 23 years in sandy soil, but seed viability decreases more rapidly in clay soils. Mimosa pigra can germinate year round if the soil is moist but not flooded. However, most germination takes place at the start and end of the wet season. Growth in seedling is rapid, and flowering occurs between 4 and 12 months after germination. The process from flower bud to ripe seed takes about five weeks.

Tien said there are several thousands hectares of this invasive tree in the southern province of Dong Nai and the seeds may have been brought to HCM City by the Dong Nai River. If not destroyed timely, this tree will spread quickly in HCM City because the city has many rivers and canals.

Vinh Giang