Stachytarpheta mutabilis (Jacq.) Vahl

Vahl, J. (1804) Enumeratio Plantarum 1 : 208.

Red Snakeweed; Snakeweed, Red; Snakeweed; Pink Snakeweed; Snakeweed, Pink

Usually flowers and fruits as a shrub about 1-3 m tall.

Leaf blades about 7-11 x 4-6 cm. Twigs, petioles and both the upper and lower surfaces of the leaf blade clothed in pale hairs. Leaf blades conspicuously toothed with about 20-25 teeth on each side. Base of the leaf blade not toothed, tapering gradually into the petiole. Upper surface of the leaf blade arched between the main lateral veins and reticulate veins. Scattered yellowish cup-shaped glands present on the upper surface of the leaf blade.

Inflorescence about 30-40 cm long, axis 3-4 mm diam., only a short section of the spike producing flowers (7-10) at any one time. Calyx and corolla unequally lobed. Calyx tubular, about 8-14 x 2-3 mm, lobes about 0.5 mm long. corolla tube about 15-20 x 1.5-3 mm, lobes spreading to about 13 mm diam. Inner surface of the corolla tube, particularly around the throat, clothed in hairs. Stamens two, staminodes two, filaments pubescent. Anther locules divaricate, borne one above the other with their long axes in line. Pollen grains +/- triangular in transverse section. Style usually recurved at the apex. Stigma peltate, mushroom-shaped.

Fruits about 5-8 x 1.5-3 mm, +/- immersed in the infructescence axis which is 30-60 cm long. Each fruit contains two elongated black nuts or nutlets which could easily be mistaken for seeds. Each nut or nutlet about 5-8 x 1.5-3 mm, completely enclosed by bracts and the persistent calyx, and contains one seed. Testa thin, cream or white and much thinner than the hard brown wall of the nut.

Cotyledons +/- triangular, about 5-9 x 5-7 mm. First pair of leaves elliptic-ovate, opposite, margins toothed, both the upper and lower surfaces sparsely clothed in pale +/- prostrate hairs. At the tenth leaf stage: all plant parts clothed in pale septate hairs. Leaf blade elliptic to almost orbicular, apex obtuse, base narrowly attenuate very gradually tapering into a short petiole. Seed germination time 52 to 237 days.

An introduced species originally from South America, the West Indies and Cuba, now a pantropic weed. naturalised in NEQ, CEQ and southwards as far as south-eastern Queensland. Altitudinal range from near sea level to 800 m. Grows in disturbed areas in rain forest particularly along roads but is more common as a weed on agricultural land.

This species may have medicinal properties.

This species has been used medicinally in Indonesia. Cribb (1981).