Macroptilium atropurpureum (DC.) Urb.

Urban, I. (1928) Symbolae Antillanae seu Fundamenta Florae Indiae Occidentalis 9: 457.

Bean, Purple; Macri; Siratro; Purple Bean

A slender vine not exceeding a stem diameter of 2 cm.

Most plant parts hairy, clothed in prostrate hairs. Leaflet blades about 3-6.4 x 2-4.5 cm, lateral leaflet stalks about 0.3-0.6 cm, middle leaflet stalks about 0.8-1 cm long. Compound leaf petiole about 2.5-8.5 cm long. Stipules triangular, about 3-7 mm long. Stipels filiform, hairy, about 1-3 mm long.

Inflorescences up to about 20 cm long. Flowers produced only at the end of each inflorescence. Flowers about 23-25 mm diam, +/- sessile. Each flower subtended by 3 hairy bracts about 5 mm long. Calyx tube about 6 mm long, lobes about 2 mm long. Petals: standard about 15-18 mm long; wings about 23 x 11 mm; keel about 17 mm long. Stamens 10, the filaments of nine stamens fused to form a tube about 13 mm long, open on one side. Free filament section about 3-7 mm long. Anthers about 1 mm long. Pollen yellow. Ovary about 8 mm long. Style abut 12 mm long. Base of the ovary surround by a disk, the plane of the upper margin oblique.

Fruits about 9-9.5 x 0.4-0.5 cm, calyx persistent at the base. Seeds reniform, about 2 x 4 mm, testa cream with dark brown markings.

First pair of leaves simple (unifoliolate) with the petiole about as long as the blade. Stipules about 2 mm long. Third leaf trifoliolate. At the tenth leaf stage: leaflet blades ovate, all leaflet blades +/- similar in size, apex mucronate, base +/- cordate. Margin of the middle leaflet slightly sinuate to entire. Margins of the lateral leaflets often with a large rounded tooth on one side of each leaflet towards the base. Upper and lower surfaces of the leaflet blades clothed in pale appressed hairs. Stalk of the middle leaflet longer than those of the lateral leaflets. Stipules lanceolate, about 4 mm long, green, spreading, clothed in appressed hairs. Stipels present. Stems twining, clothed in pale, backward-pointing hairs. Taproot swollen. Seed germination time 20 days.

An introduced species originally from tropical America now naturalised in NT, CYP, NEQ, CEQ and southwards as far as coastal central New South Wales. Altitudinal range in NEQ from near sea level to 800 m. Now more or less pantropic being naturalised in most tropical regions of the world.

One of the most important pasture legumes for subhumid parts of the state (Qld). Palatable, adapted to most soils excluding heavy clays, and persistent providing it is not overgrazed and is occasionally allowed to produce a seed crop and re-establish. Hacker (1990).