Stachytarpheta jamaicensis (L.) Vahl

Global description

Stachytarpheta jamaicensis is an herb or small shrub 50 to 80 cm high, with more or less horizontally spread branches, upright up at the end. The branches are smooth, sometimes sparsely hairy on young parts. The leaves are opposite, light green rather dull, oval, with serrated margin. The flowers are pale blue, arranged along an erect spike, 15 to 30 cm long. They gradually bloom along the axis by small groups of 3 to 6 flowers.
 
Cotyledons

Cotyledons carried by a long petiole, 3 to 4 mm. The leaf blade is hairy, oval lanceolate, with a prominent midrib. Their size is 7 to 8.5 mm long and 6.5 to 8 mm wide. The base is wide angled, the apex is rounded.
 
First leaves

First leaves simple, opposite and sub sessile. The oval blade is 8.5 to 10 mm long and 6 to 7 mm wide. It is covered on its upper face with stiff hairs. The base is wedged and the apex is wide or acute. The margin is serrated.
 
General habit

Erect growth habit. This herb is sometimes woody at the base and can take the appearance of a small bush, 30 to 100 cm high. The branches are ascending, green, purple or almost black.
 
Underground system

Solid, often lignified taproot.
 
Stem

Stem is cylindrical, solid, green color, sometimes tinged with purple, and glabrous. The young stems are sometimes quadrangular with sparse pubescence. The base of the stem is quickly lignified.
 
Leaf

Leaves simple, opposite and petiolate. The leaf blade is elliptical or slightly oval. It is glabrous, rounded at the apex, suddenly attenuated in the wide corner at the base and decurrent along the petiole. It measures 3 to 7 cm long and 1.5 to 4.5 cm wide. The margin is serrated (tines more or less oval and apiculate). The pinnate ribs are depressed on the upper surface and protruding on the underside. Both sides are glabrous.
 
Inflorescence

Spikes 20 to 60 cm long, erect and curved at the top, with a rachis reaching up to 5 to 6 mm thick at the fruiting.
 
Flower

Sessile flowers are first applied to the surface of the rachis and inserted in the elongated alveoli as the rachis thickens at fruiting. The narrowly ovate acuminate bracts are applied against the calyx. They are 5 to 6.5 mm long and 1.3 to 1.5 mm wide and have a scarious margin. The calyx is as long as the bracts, with 5 short tines. The tubular corolla is of a color ranging from pale blue to dark purple with a white interior. It consists of 5 unequal petals and measure 5 to 10 mm long. The lobes of the two upper petals are wider than those of the 3 lower petals. The 2 stamens are 1.5 mm. The ovary is surmounted by a filiform style reached the top of the corolla tube.
 
Fruit
 
The fruit is an oblong capsule, dark brown, which remain included in the persistent calyx, inserted into the fruit-bearing rachis. It measures 3 to 5 mm long, with a small terminal beak and contains 2 to 3 seeds. At maturity the fruit separates into two indehiscent capsules.

Origin

Stachytarpheta jamaicensis is native to Central America, Northern South America and the Caribbean.

Worldwide distribution

This species has been introduced in some African countries (CAR, Ivory Coast, Kenya, Mozambique), all Indian Ocean islands (Comoros, Mayotte, Madagascar, Seychelles, Reunion, Mauritius), India, South East Asia, Eastern Australia, and many Pacific islands.

https://www.gbif.org/fr/species/2925463