A. sessilis is an annual or perennial herb, of 0.2-1 m high, with strong taproots. The stems are generally prostrate, creeping, often rooting at the nodes, sometimes floating or ascending at the tips, cylindrical and slightly hairy, with numerous, erect branches. The leaves are simple, opposite, shortly petiolate or sessile, broadly lanceolate or spatulate to almost linear, 0.6-5 cm long, and 0.3-1 cm wide. They are attenuated at the base, and the apex is acute to blunt, with entire, glabrous or pilose (thin, fine, articulate hairs) margins. The inflorescences are dense, sessile, silvery-white clusters of compressed spikes in the leaf axils;perianth segments are equal in length, acute, 1.5-2.5 mm long with a short point. Bracts are ovate, concave, 0.3-1 mm long and persistent;bracteoles are oblong-ovate, 1-1.5 mm long, may be acute, and not deeply lacerated. Sepals are 2-3 mm long, white or purplish, glossy with a green base, glabrous or with a few long hairs, and a strong midrib. The fruits are indehiscent, a small, flattened, obcordate or obovate utricle, 2-2.5 mm long, enclosing the seed. Seeds are dark-brown to black, disc-shaped and shiny, about 0.8-1 mm in diameter. They are light sensitive and the average number of seeds per plant is ca 2000.
Related invasive species
- Alternanthera sessilis
Related Farm Practice
- Light
- Rooting
A. sessilis is a pioneer species typically growing on disturbed areas and in wetland habitats, and regarded as a fast-growing highly invasive weed. It is adapted to grow on a range of soil types ranging from poor sandy or alkaline soils, to loam or black cotton soils. It is also able to grow in seasonally-waterlogged areas as well as in areas with extreme dry conditions (Holm et al., 1997). A. sessilis can be found invading floodplain wetlands, margins of rivers, streams, canals, ditches, ponds, reservoirs, tanks, marshes, swamps, wet low-lying ground, ephemeral pools, seasonal pans and damp forest. This species is also a weed in fields with sorghum, millet, Eleusine spp., maize, cotton, cassava, cereal crops, pastures, and vegetable farms (Gupta, 2014). Consequently, this species has been listed as invasive in India, South Africa, Namibia, Spain, Hawaii and many other islands in the Pacific Ocean (see distribution table for details). It is also listed as a noxious weed in the United States (USDA-NRCS, 2014).