Family: - Fabaceae.Names:
Other names:Annual Yellow Sweet Clover
Summary:Usually erect, almost hairless, often smelly, annual to biennial legume about 50 cm tall with trifoliate leaves with the central leaflet on a longer stalk, angular stems and clusters of small, yellow, pea type flowers in spikes in spring.
First leaves:The first leaf is heart shaped with a notched tip and is hairless. The second and nest few leaves have 3 heart shaped, smooth edged leaflets. Later leaves have more elongated leaflets with toothed edges.
Leaves:Alternate. Three leaflets with the central leaflet on a longer stalk than the 2 side leaflets. Usually with a strong vanilla like odour when crushed.
Stems:Erect, spreading or sprawling. 100-1000 mm tall, angular. Almost smooth and hairless.
Flower head:Dense, narrow raceme, 10-40 mm long on an erect stalk that is 10-30 mm long and arises from the leaf axils.
Flowers:Yellow, pea type, small, 2-3 mm long.
Fruit:Olive green, leathery pod, swollen or slightly flattened, egg shaped to almost globular, 2-3 mm long by 1.5-2 mm wide, with a network of veins to being deeply wrinkled. The pod is on a pendulous short stalk. 1-2 seeds per pod. Does not open to drop seeds when it falls at maturity.
Seeds:Globular, flattened, 1-2 mm diameter with a depressed or somewhat grooved face. Surface pimply and hairless with a white stripe(aril).
Roots:Short taproot and many spreading laterals with nitrogen fixing nodules.
Key Characters:Raceme 10-40 mm long and longer than the leaves. Calyx 5 nerved. Yellow flowers 2-3 mm long on long, 10-60 mm peduncles. Pod 2-4 mm long, obtuse and reticulate to rugose.
Physiology:Coumarin causes the odour.
Flowering times:Late winter to early summer in western NSW.
Seed Biology and Germination:Seed remains viable in the soil for some years.
Origin and History:Mediterranean. Southern Asia.
Distribution:ACT, NSW, NT, QLD, SA, TAS, VIC, WA.
Soil:Most abundant on sandy soil, near the sea, lake margins, river banks, on limestone soils, heavy grey clay and granite outcrops.
Plant Associations:Open Mitchell grass, Black Box, Mallee and many other communities.
Detrimental:Weed of roadsides, cultivated areas, pastures, hay, crops, coastal islands, coastal woodlands, granite outcrops, and disturbed areas.
Toxicity:Possibly toxic but unconfirmed.
Symptoms:Lethargy and paralysis prior to death.
Treatment:Don't graze milking cows or stock for slaughter on infested areas.
Legislation:Seed is a prohibited impurity of wheat for human consumption.
Management and Control:Cultivation controls seedlings. Prevent seed set by heavy grazing with animals not destined for slaughter. Hormone herbicides are effective on young actively growing plants. If present at harvest, weed seed should be removed from the grain without delay. Seed remains viable in the soil for some years so repeated control over a number of seasons is required.
Thresholds:Low numbers can cause grain contamination or taint milk and meat products.
Eradication strategies:Isolated plants can be removed manually. Small infestations in grassed areas can be treated annually in late winter by spraying with 1 part of Tordon 75-D in 100 litres of water. Larger infestations can be cropped with cereals and treated with sulfonyl urea herbicides.
Herbicide resistance:Biological Control:
Plants of similar appearance:Lucerne (M. sativa) looks similar but has purple flowers and little odour when crushed and is perennial.
References:Auld, B.A. and Medd R.W. (1992). Weeds. An illustrated botanical guide to the weeds of Australia. (Inkata Press, Melbourne). P168. Photo.
Acknowledgments:Collated by HerbiGuide. Phone 08 98444064 or www.herbiguide.com.au for more information.