Richardia scabra L.

Global description

Richardia scabra is an annual, herbaceous, prostrate plant, 20 to 60 cm high. Quadrangular stems, branched, colored (red-brown), very hairy. Taproot. Leaves opposite, decussate, entire, 1 to 4 cm long, broad, hairy. White flowers grouped in terminal glomerules (5-25 flowers per inflorescence).The corolla consist of 4 to 6 lobes and a trilocular ovary whose style terminate by a trifid stigma. Reproduction mainly by seed.

Cotyledons

Cotyledons subsessile, with an oval blade, with rounded tip and a stipular flange at the base.
 
First leaves

The first leaves are simple, opposite, short-stalked, perpendicular to the lamina of cotyledons. The leaf blade is ovate-oblong to oval elliptical, with a wedged apex, base attenuated into a petiole. The midrib is well marked taking a reddish color towards the petiole, veins and margin are strongly scabrous.
 
General habit

Richardia scabra is a prostrate or erect annual herb, profusely branched from the base, and reaching up to 60 cm in height.
 
Underground system

The main root is a taproot.
 
Stem

The stem is thick, with quadrangular section, covered with long dense white hispid hairs, erect or prostrate, reaching up to 60 cm tall, with loose branching.
 
Leaf

The leaves are simple, opposite, decussate, sub sessile, with ovate to elliptic lanceolate blade, 1.5 to 4.5 cm long and 0.7 to 2.5 cm wide, thick and membranous, base attenuate into a short poorly individualized petiole, wedged and mucronate apex, more or less scabrous and hirsute on both sides, margin ciliated to scabrous; stipular collar between the petioles, 2-4 mm high and 3-4 mm wide, hispid, with 1 to 5 subequal filiform appendages, 3 to 4 mm long with ciliate margin.
 
Inflorescence

Inflorescence in terminal clusters, 0,8-1,5 cm in diameter, sessile, subtended by the pair of terminal leaves; the last two leaves being shorter and smaller than the previous pair and is arranged perpendicularly.
 
Flower

Small tubular flowers, 2 to 8 mm long, usually white in color; calyx 2 to 2.5 mm long with 4 to 6 lobes (1 mm), scabrous; corolla with a basal tube surmonted by 4 to 6 acute triangular lobes, 2 to 3 mm, usually white in color. Each flower has 3 to 6 stamens located between the lobes of the corolla; ovary subglobose with 3 loculus, containing 1 ovule per loculus. It is topped by a style ending into a trifid stigma
 
Fruit

The fruit is a trilocular, ovoid to subglobose capsule, 1.5 to 3.5 mm long and 1 mm in diameter, with a pronounced scabrous appearance. Each compartment contains one seed.

Seed

The seed is oblong to triangular, thick, hollow and has 2 longitudinal lobes. The ventral surface has a wide longitudinal groove. It is 2 to 3 mm long and 1.5 mm wide. The integument is glabrous, greyish-beige, with fine white dots and numerous short, thick spines.

Origin

Richardia scabra is native to Central and South America.
 
Worldwide distribution

It is present in many tropical regions (Central America and the Caribbean, South America, South and East of the USA, Southern Africa, Madagascar, India, Southeast Asia, Indonesia). Introduced in China in the 1980s and in Reunion in 2015.

https://www.gbif.org/fr/species/5337491