Acmella caulirhiza Delile

Global Description
 
Acmella caulirhiza is a perennial herbaceous plant, with the stem more or less trailing then erect. The leaves are simple, opposite, decussate. The lamina is oval, attenuated in a petiole at the base, giving the impresssion of a winged petiole; the apex is acute and the margin serrated. The whole plant is glabrous to slightly hairy. The inflorescence is a terminal capitulum, at the end of a long peduncle. The capitulum is conical, with 10-15 yellow ligulate florets on the periphery and a lot of yellow tubulate florets in the center. The fruit is an achene without pappus.
 
Growth habit
 
Acmella caulirhiza is a perennial herbaceous plant, with more or less creeping stems, easily rooting at the nodes, then erect. It measures up to 40 cm high.
 
Underground system
 
The main root is a taproot. The nodes of the stem in contact with the ground easily develop small adventitious roots.
 
Stem
 
The stem is full, of quadrangular section. It is 0.5 than 2.8 mm in diameter. It is smooth to slightly hairy.
 
Leaf
 
The leaves are simple, opposite, decussate. They are carried by a petiole, 1 to 15 mm long. The lamina is oval in shape, 1.3 to 5 cm long and 0.8 to 4 cm wide. The base is attenuated and decurrent along the petiole which seems winged. The apex is acute, the margin serrated with some sparse stiff hairs. Both sides are glabrous to slightly hairy.
 
Inflorescence
 
The inflorescence is a terminal capitulum at the end of a peduncle, 2 to 7 cm long and 1 to 2 mm in diameter, sparsely hairy. The capitulum is conical, it is above 4.5 to 10 mm and a diameter of 4.5 to 9 mm. It is subtended by 9-13 bracts in two rows. They are lanceolate to oval and 3.5 to 6 mm long and 1 to 2 mm wide, rounded or acute apex and entire or sinuate margin with a few sparse stiff hairs. In between the florets are membranous paleoles, 2.7 to 4.5 mm long and 0.5 to 1 mm wide, with rounded or acute apex, more or less ciliated.
 
Flowers
 
The florets of the periphery are 10 to 15 in number, ligulate, yellow to orange-yellow in color. They are essentially the same size as the involucral bracts. The corolla is formed of a pipe at the base, 2.2 mm long and more or less hair, surmounted by a bilobed ligule, the top 1.4 to 2.3 mm long and 0.6 to 1.8 mm wide. The florets of the periphery are female, style is bifurcated, filiform.
The central florets are very shady (68 to 254), tubulate, yellow to orange yellow. The corolla is formed of a tube, 1 to 2 mm long, ending in 5 triangular lobes. The central florets are hermaphrodites. The anthers are black, the style is bifide, thickened, 1 to 1.5 mm long.
 
Fruit
 
The fruit of the peripheral florets is an elongated trigonal achene, 1.3 to 2.1 mm long and 0.5 to 0.8 mm in diameter, glabrous or sometimes slightly ciliated. It has a circular bead on the top, usually without pappus or sometimes with bristles.
The fruit of the central florets is an alkene, 1.5 to 2.4 mm long and 0.5 to 0.8 mm in diameter, generally smooth to slightly ciliated, without pappus.

Benin : Acmella caulirhiza flowers and fructifies from July to October.

Acmella caulirhiza is a perennial or annual species. It is propagated by seeds, but can also easily be propagated by cuttings.

 

 Table of comparison between species of the genus Acmella and Spilanthes

	Acmella caulirhiza	Acmella oleracea	Acmella uliginosa	Spilanthes costata
Cyclicity	perenial	annual	annual	annual
Growth habit	trailing	erect	erect	erect
Diam. capitulum	4,5 - 9 mm	>10mm	4-6 mm	>10 mm
Color of capitulum	yellow-orange	yellow orange	yellow orange	white
Composition of capitulum	ligulate and tubulate	tubulate	tubulate or ligulate and tubulate	tubulate
Tubulate florets	5 lobes	5 lobes	4 lobes	4 lobes
Achene	without pappus	pappus 2 bristles	pappus 2 bristles

Comoros: Absent.
Mauritius:
Reunion: Acmella caulirhiza thrives in moist sites, along roads, on the edge of streams in pastures and lawns and in forests.
Madagascar:
South Africa: Acmella caulirhiza grows in damp places. Marshy or seasonally damp sites, riverbanks, cultivated areas, forest edges. A pioneer plant that can colonise bare soil, and a very common plant in damp ruderal areas.

 

Origin
 
Acmella caulirhiza is native to tropical and subtropical Africa.
 
World distribution
 
Acmella caulirhiza occurs throughout tropical and subtropical Africa, Cameroon, Ivory Coast, Zaire, Ethiopia, Tanzania, Sudan, Madagascar, Kenya, Uganda, South Africa. It is also very common in the Mascarene Islands (Mauritius, Reunion).

Medicinal: Acmella caulirhiza is used against malaria in Cameroon. It is also reported to have stimulating property, diuretics and anti-asthmatics.

Herbarium pictures ReCOLNAT: https://explore.recolnat.org/search/botanique/simplequery=Acmella%2520caulirhiza