Acmella uliginosa (Sw.) Cass.

Global description

Acmella uliginosa is a small annual herbaceous plant, very branched in its upper part, which grows on wet or even marshy grounds. It is a glabrous or very slightly pubescent plant, with simple and opposite leaves, with clearly spaced pairs of leaves along the stem. The inflorescences are conical yellow heads, borne by a very long pedunclesthat extend beyond the corresponding leaves. They are located towards the top of the plant. The achenes with ciliated margin are provided with a pappus of 2 short bristles. They are scattered by animals.

Cotyledons

The cotyledons are petiolate, with an oval blade and apex slightly emarginate, fleshy, glabrous and smooth.

First leaves

The first leaves are simple and opposite. The lamina is light green, oval, the base cunate and apex acute, irregularly and weakly toothed. It is borne on a green petiole.

General habit

Annual branched herb, 15-40 cm tall (up to 1 m in Indonesia). Erect or prostrate with rooted base then erect, densely branched in its upper part.

Underground system

The main root is pivoting, the secondary, adventitious are fasciculate.

Stem

The stem is cylindrical and fleshy, it is branched, prostrate first and then erect. Stems and twigs light green, sometimes slightly striated, glabrous or occasionally with some large white hairs appressed.

Leaf

Leaves simple, opposite, well spaced, 1 to 10 cm long by 0.5 to 6 cm wide, petiolate, with a narrow blade, lanceolate to ovate lanceolate. The apex of the lamina is obtuse to acute, the base is broad, rounded to truncate; the margin is lightly and irregularly toothed. Leaf-blade almost glabrous, with few short hairs, sparse and appressed on the upper face, pubescent on the underside, especially on the veins.

Inflorescence

The flowers are gathered in conical heads (5 to 6 mm in diameter, 7 to 11 mm long) solitary at the end of the stems or at the axils of the upper leaves. They are borne by a long peduncle (1 to 12 cm long) which elongates with ripening, angular, bearing large white hairs, short and appressed. The involucre is formed of 5 to 10 green bracts, arranged in one row, less frequently in two rows, a little thickened, oval and obtuse end, margin finely ciliated, but glabrous elsewhere.

Flower

The flower head includes 2 types of florets. Occasionally, a few irregular, 2 to 2.5 mm long, yellow-shiny, female ligulated florets arranged in a row on the periphery, ligule ending in 3 to 4 lobes, ovary compressed with 2 curved stigmas. In the center, tubular florets hermaphroditic (1.3 to 1.5 mm long), numerous, regular, yellow-brilliant, with 4 (-5) terminal lobes, 4 (-5) stamens with brown anthers, not exceeding the corolla and ovary similar to ligulate flowers. A carinated scale (3 mm x 1 mm) surrounds each tubular floret.

Fruit

The fruit of the ligulate florets is a truncated ellipsoid achene, with the keeled ventral side. The fruit of the tubular florets is a flattened achene of elliptical shape, truncated at the top, 2 mm long by 1 mm wide, often weakly curved, with smooth and black faces, with ciliated membranous margin. The apex, glabrous or weakly hairy, has a pappus formed of 2 very thin, erect, little visible hairs, 0.3 mm long.

Origin

Acmella uliginosa is native to South America and the Caribbean.

Worldwide distribution

Acmella uliginosa is now a pantropical species.

https://www.gbif.org/species/5386720