Macroptilium lathyroides

phasey bean


Macroptilium lathyroides

(L.) Urb. 1928

pronounced: mak-rop-TILL-ee-um lath-ee-ROY-deez

(Fabaceae — the pea family)

subfamily: Faboideae - the bean sub-family


common name: phasey bean

Macroptilium is from the Greek μακρος (makros), large and πτιλον (ptilon), a downy feather; lathyroides means ‘resembling Lathyrus’ (λαθυρος), a kind of pulse.

Like siratro, this is another agricultural escapee. Originally from tropical America, including the Caribbean islands, it was introduced into India, Australia, Africa and southern USA and planted as a pasture legume. It is now naturalized in many places in the tropics, and is a weed of roadsides, disturbed areas, riverbanks, grasslands and open woodlands. In Australia it is most common in the northern parts of the Northern Territory, eastern Queensland, and north-eastern NSW. The plants photographed were growing by the roadside in Nelly Bay.

This is an herbaceous annual or short-lived perennial, with an erect habit, up to about 1 metre tall, with the lower portion of the stem tending to become woody with age. Older plants occasionally develop climbing or twining branches towards their tips, if the plant is growing amongst taller vegetation. The stems are appressed pubescent, and the alternate leaves are trifoliate, on petioles 1 – 5 cm long, with a pair of stipules at the base of each of the leaf stalks. The leaflets are 8 – 10 cm long by 2 – 3.5 cm wide, and are lanceolate, elliptic or narrowly ovate in shape, the tips of the leaves acute or acuminate, with entire margins, the lateral leaflets sometimes slightly lobed towards the base. The upper surfaces are glabrous, and the lower ones pilose.

The flowers, occurring throughout the year, are papilionaceous, about 1.5 cm long, on very short pedicels, the standard bright red or purplish red (rarely white), the keel petals tinged green, red or white, the keel spirally twisted, and are borne on a semi-erect spicate raceme about 15 cm long, on axillary peduncles that are up to 30 cm long.

The pods are elongated and narrow, 8 – 10 cm long by only 2 – 3.5 mm wide, and covered with appressed hairs. As they mature, they turn from green to brown in colour, and become strongly twisted. They each contain 20 – 30 seeds that are about 3.5 mm long by 3 mm wide, brown, or mottled brown and black, with a slightly pitted surface. The pods are explosively dehiscent, and the seed can be projected for several metres.

In agriculture, the plant is used as a pioneer forage, but can be made into hay or silage when mixed with a grass – on its own, it is prone to leaf drop. It is a very effective nitrogen fixer, and can be used as a green manure or cover crop in rotations.

Photographs taken in Nelly Bay 2016
Page last updated 31st January 2019