Calamus plant form is a perennial herb with a special aroma. Rhizome fat, 10-15mm in diameter, transverse, branched, with a majority of links, nodes bearing a majority of fibrous roots. Leaves from the base, simple leaves, rows of 2 columns, base clasping, sword-shaped, leathery, 50-80cm long, sometimes up to 150cm wide, 0.8-1.5cm wide, apex pointed, midvein obviously raised.May-July flowering, within the spikes terete, 3-8cm long, 7-15cm wide, leafy bracts 1, flowers small, dense, yellowish-green, perianth segments 6. Stamens 6. Ovary 2-4 cells. Berry obovate, red when ripe.

Chinese medicine water caltrop visible rhizome flat cylindrical, less branching, 10-20cm long, 1-1.5cm in diameter. surface white to brown-red, with fine longitudinal lines. The internodes are 0.2-1.5cm long, and the upper side has concave dot-like root scars. Hard, spongy fracture surface, white or light brown, endothelial ring is obvious, there are most of the small cavities and vascular bundles of dots. The odor is strong and peculiar. Taste bitter, pungent.