Amaranthus spinosus L.

Linnaeus, C. von (1753) Species Plantarum 2: 991. Type: Habitat in Indiis.

Burr, Needle; Needle Burr; Spiny Amaranth; Spiny Pigweed

Usually flowers and fruits as a weedy plant about 1 m tall.

Twigs spiny, the spines about 1-2 cm long and produced near the point of attachment of the leaf petioles like spinose stipules. Leaf blades about 2.5-7.5 x 1-2.5 cm.

Inflorescence densely flowered, each flower subtended by a bract. Tepals white or translucent except for a green midrib, papery, tapering to a fine point at the apex. Male flowers: Flowers about 2 mm long, tepals about 2 mm long. Anthers about 1 mm long on short filaments. Female flowers: Flowers about 1.5-2 mm long, tepals about 1.2 mm long. Ovary, style and stigma about 2 mm long. Ovary green, 2-3-lobed, the 'equator' marked by a line. Styles very short.

Fruit circumscissile, about 1.5-2 mm long, splitting +/- at the 'equator'. Perianth persistent at the base and stigmas persistent at the apex. Seeds about 1 x 1 x 0.5 mm. Embryo +/- C-shaped, located on the margin of the seed just inside the testa. Cotyledons about as wide as the radicle.

Cotyledons linear, about 4-9 x 1-2.5 mm. Petioles slender. First pair of leaves ovate, apex retuse, borne on long slender petioles. At the tenth leaf stage: stems spiny, spines channelled and about 5-10 mm long. Petioles long and slender. Leaf blades emarginate at the apex. Seed germination time 8 days.

An introduced species, originally from tropical America, now naturalised in NT, CYP, NEQ, CEQ and southwards as far as south-eastern Queensland and coastal central New South Wales. Altitudinal range from near sea level to 820 m. Grows as an agricultural weed and in disturbed areas in rain forest.

Suspected of being poisonous to livestock. Everist (1974).

Despite the spine, which cause discomfort for the consumer, this plant has been used both as a spinach substitute and in medicine. Cribb (1981).