Stachytarpheta cayennensis (Rich.) Vahl

Vahl, J. (1838) Enumeratio Plantarum 1: 208.

Snakeweed

Usually flowers and fruits as a shrub about 1-2 m tall but also flowers when smaller.

Leaf blades about 4.5-10.5 x 2.5-4.5 cm, petioles about 3-5 mm long. Stem and petioles clothed in prostrate hairs and erect glandular hairs. Upper surface of the leaf blade bullate. Hairs present on the midrib and main lateral veins but the body of the leaf glabrous. Leaf blades conspicuously toothed with about 20 teeth on each side. Base of the leaf blade not toothed, tapering gradually into the petiole.

Inflorescence up to 28 cm long, axis about 1-3 mm diam., furrows from the immersed flowers nearly as wide as the axis. Calyx tubular, about 4-6 mm long, 2 mm diam., lobes tooth-like, about 0.5-1 mm long. Corolla tube about 6-7 mm long, lobes about 2-4 mm long. Stamens two, staminodes two, filaments hairy. Anther locules borne one above the other with their long axes in line. Pollen grains Y-shaped or 3-bladed. Ovary about 1-1.2 mm long, locules 2. Style about 5 mm long. One ovule per locule.

Fruits about 3-4 x 1.5-2 mm +/- immersed in the infructescence axis. Each fruit contains two elongated black nuts or nutlets which could easily be mistaken for seeds.

Cotyledons ovate, about 8 x 6 mm, petiole quite long. First pair of leaves opposite, margin toothed, leaf blade hairy at least on the lower surface. At the tenth leaf stage: leaves ovate, elliptic or obovate, margin toothed, leaf blade punctate on the underside, gradually tapering into the petiole. Upper surface of the leaf blade arched between the lateral veins and reticulations. Seed germination time 10 to 59 days.

An introduced species originally from tropical America, now a pantropic weed. naturalised in WA, NT, CYP, NEQ, CEQ and southwards as far as south eastern Queensland. Altitudinal range in northern Australia from near sea level to 750 m. Grows in disturbed areas in rain forest particularly along roads but is more common as a weed on agricultural land.