Stachytarpheta cayennensis (Rich.) Vahl

Global description

Stachytarpheta cayennensis is a bushy herb or sub-shrub with very branched, tortuous, almost succulent stems, often dark in colour. The leaves are simple, opposite, sometimes whorled, oval to elliptical, with a toothed margin and embossed surface, dark green. The inflorescence is a long cylindrical spike, usually twisted, bearing sessile, light blue flowers with a corolla fused into a bent tube ending in 5 rounded lobes.

Cotyledons

The cotyledons are oval, with a truncated base and rounded top. They are fleshy in appearance.

First leaves

The first leaves are simple, opposite, short-stalked. The blade is broadly oval with a toothed margin in the lower 2/3. They are thick and fleshy.

General habit

Stachytarpheta cayennensis is a herbaceous perennial, quickly becoming a small, highly branched bush, usually reaching 0.5 to 1.5 m in height, sometimes up to 2.5 m.

Underground system

The root is a deep taproot.

Stem

The stem is cylindrical to angular, solid, almost succulent, fibrous and very resistant to being pulled up. It is highly branched, and often tortuous, with horizontal or hanging branches. The colour is yellowish brown, grey or dark purple, almost black. It is shortly pubscent.

Leaf

The leaves are simple opposite or sometimes whorled, short-stalked or stalkless, petiole 1 to 1.5 cm long. The blade is oval to elliptic, 2 to 8 cm long and 1 to 5 cm wide. The apex is obtuse or broadly wedge-shaped, the base is gradually attenuated and decurrent along the petiole, becoming indistinct. The margin is strongly toothed with acuminate teeth, the upper surface deeply embossed, rough and scabrous. The underside is pubescent and scabrous and has very prominent veins. The leaf blade is dark green, often purplish on the lower side.

Inflorescence

The inflorescence is a long, cylindrical, linear, erect, curved or often twisted terminal spike. It is 15 to 40 cm long and 2 to 5 mm in diameter. The rachis is pubescent, with closely spaced longitudinal cells bearing the flowers and covered with a lanceolate bract. Occasionally, spherical, smooth, blue-coloured galls 8 mm in diameter develop on the rachis and resemble fruits.

Flower

The flowers are solitary, sessile, developing in the alveoli of the inflorescence rachis in the axils of the bracts, and blooming gradually from the base to the top of the spike. The calyx is a tube compressed against the axis, 4 mm long, dorsally hairy, green, scalloped posteriorly and ending in 4 to 5 unequal teeth, often dark purple. The corolla has a 5 to 7 mm long, angled tube at the base, ending in 4 to 5 rounded lobes forming an opening 5 to 10 mm in diameter. The corolla is light blue, lilac or whitish with a paler, pubescent throat. In the throat are 2 fertile stamens and 2 sterile staminodes (typical of the genus Stachytarpheta).

Fruit

The fruit is a flattened, dry, indehiscent fruit, 3.5-6 mm long and 1.5-1.8 mm wide, remaining enclosed in the calyx, light brown and slightly hairy.

Seed

The seed remains enclosed in the indehiscent fruit, it is oblong, apiculate and black.

Origin

Stachytarpheta cayennensis is native to Central and South America and the Caribbean.

Worldwide distribution

This species has been introduced to various countries in West, Central and East Africa, in the Indian Ocean it is present in Mauritius, India, Asia (China, Malaysia) and the Pacific (New Caledonia, Tuoamotu, Marquesas, Hawaii).

https://www.gbif.org/species/2925454