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Phasey bean   
 Phasey bean

Phasey bean biology
Macroptilium lathyroides
Family: Fabaceae (Pea family).

Common names: Phasey bean.


Seedlings – cotyledons are a flattened oval in shape 6 – 10 mm long and 4 – 8 mm wide, borne on stalks 4 – 5 mm long. The stem are reddish towards the base and covered in fine hairs.

Early leaves - the first and subsequent leaves have three leaflets, the terminal leaflet larger than the lower two leaflets and on a short stalk 10 – 15 mm long.

Leaves – have three lance- to oval-shaped leaflets each, 40 - 80 mm long and 10 -30 mm wide. The leaflets may have short hairs. The leaf stalk is 10 – 40 mm long.

Plants – have erect or climbing stems to 100 cm. The stems are covered in short hairs. In cotton, phasey bean can develop into a stout, branched bush to 1 m in height with robust, woody stems.

Flowers - are pea-like, 10 – 15 mm long, pink to crimson in colour, sometimes tinged with green and borne on flowering stems are up to 400 mm long. The flowers have a twisted keel (the lower two flower petals).

Seed heads – are softly hairy, linear to curved brown pods, 80 - 100 mm long and around 3 mm wide. There are up to 20 bean-like seeds in each pod, each 3 - 4 mm long, and mottled orange/brown in colour. Seeds are dispersed when the pod twists in a spiral fashion at maturity spilling the seeds.

Lifecycle/Biology: An annual species that germinates after rainfall in spring and summer, and flowers in summer and autumn.

Ecology: Found in pastures and along roadsides and found on heavy clay soils. A major weed in the Theodore and Emerald cotton areas.

The problem: A major weed of cotton in Central Queensland. Very dense populations of phasey bean can establish and compete strongly with cotton. Plants are relatively tolerant of glyphosate and are very difficult to remove from the cotton plant line. Plants can produce a lot of seed which has strong dormancy characteristics, ensuring staggered germination over many seasons.

Distribution: An occasional weed in Northern NSW, and found throughout most of Eastern Queensland.

Origin: An introduced species from Central America.

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