Global description
Cyathula prostrata is an erect or decombant plant, 20 cm to 60 cm high, sometimes more. The angular stem is covered with erect hairs. The opposite leaves, 4 to 9 cm long, are short-stalked, tinted red below and at the edge, especially when young. The leaf blade is elliptic, with the top tapered to a tip. The flowers are small and greenish, with less than 3 mm long. They are arranged in long terminal and lateral spikes. The fruit hidden in a ball of small hooked hairs are headed downward to maturity. They cling to clothing and animal hairs.
General habit
Herbaceous plant, 20 to 60 cm, sometimes larger. It is more or less erect or decumbent. The plant is branched as from the base.
Underground system
The plant has a taproot system.
Stem
The stem is quadrangular, full; it is sometimes almost cylindrical and longitudinally striated. It is pubescent with erect hairs or nearly glabrous.
Leaf
The leaves are simple and opposite, sometimes tinged with purple beneath and at the edge, especially when young. The petiole is 5 to 15 mm long and pubescent. The leaf blade is elliptic, obovate, often with a diamond shape for the big leaves. It measures 1.5 to 8 cm long and 1 to 4.5 cm wide, wedged base, acute or acuminate apex. The margin is entire. 5-6 pairs of parallel curved lateral veins. Both sides are pubescent to sub-glabrous in older leaves.
Inflorescence
The inflorescence is arranged in terminal spikes of up to 35 cm long, or lateral at the axils of the upper leaves, but smaller in size. The rachis is pubescent. The flowers are grouped in small dense glomerules at the top, spaced quickly towards the base. These glomerules are first erect towards the top then flips over and apply to the axis of the spike after flowering.
Flower
The floral glomerules are subglobose, shortly stalked, with basically a small, apiculate, oval bract at the base. They are composed of 2 to 3 fertile ovoid flowers of 2 to 3 mm, subtended by oval pubescent bracts, mucronate at the top. The tepals are 2 to 3 mm long, elliptical oblong, trinervate. The lateral flowers are placed between two small sterile accrescente flowers which are transformed into bracts (7 to 8 per flower). These sterile flowers are reduced to crooked edges assembled at the base on a pedicel of 1 mm. They are long-acuminate, acute of 1 to 2 mm, curved hook. The ovary has only one ovule. It is more or less obovoid, and 0.7 mm long. The style is slender, with a rounded stigma.
Fruit
The fruit is an ovoid capsule, very thin with almost membranous pericarp, containing only one seed. It is surmounted on style.
Seed
The seed is lenticular ovoid, 1.5 mm long, brown, shiny and smooth.