Burr Medic

Medicago polymorpha L.

Synonyms - Medicago hispida Gaertn., Medicago denticulata.

Family: Fabaceae.

Names:

Medic is from the Latin medica meaning Lucerne and derived from the Greek mediche because it was introduced to Greece from the Media region in the Old Persian Empire.
Burr Medic because it has obvious burrs.

Other names:

Burr Clover
California Burr Clover
Creeping Burr
Medic Burr
Medic Clover
Rough Medic
Toothed Burr Clover
Toothed Burr Medic
Toothed Medic
Trefoil

Summary:

Burr Medic is a low-growing, almost hairless, sprawling herb with leaves divided into 3 heart-shaped leaflets each 4-25 mm long. The terminal leaflet is on a longer stalk than the two side leaflets. It has clusters of 2-7, small, yellow, pea-type flowers with petals that are only 3-5 mm long. The fruit is a small, greenish-brown burr with 1-6 tight coils that are often spiny.
Native to the Mediterranean region, Burr Medic is a common weed of gardens, pastures and roadsides and flowers in winter and spring.

Description:

Cotyledons:

Two. Oval. Tip round. Sides convex. Base tapered to squarish. Surface hairless. No petiole.

First leaves:

The first leaf is kidney shaped, 10-20 mm long. Stalked. Tip and base indented. Hairless. Later leaves have 3 leaflets.

Leaves:

Alternate. Three leaflets on the end of a long leaf stalk. Stalk of the middle leaflet is longer than the outside ones.
Stipules - Leafy, narrowly egg shaped, finely to deeply toothed, outgrowth 4-10 mm long at base and attached to the petiole. Tapers to a pointed tip.
Petiole - Long and hairless.
Blade - Of leaflet, oval to heart or wedge shaped, 5-25 long x 4-17 mm wide, toothed near tip, smooth edged near the base. Tip occasionally blunt but usually notched and the midrib sticks out to form a small spine. Always hairless on the upper surface and hairless or occasionally with sparse hairs on the lower surface.

Stems:

Prostrate or upward bending at the ends, square, branched from base, 200-1000 mm long. Hairless.

Flower head:

Axillary raceme, 4-6 mm long, with clusters of 2-10 flowers on stalks, 5-20 mm long that may have a terminal awn.

Flowers:

Pea type, yellow, small, 3-6 mm long.
Bracts - Small, persistent.
Ovary -
Calyx - Tubular with 5 lobes. Tube 1-2.5 mm long. Lobes 1-3 mm long, triangular to awl shaped.
Petals - Yellow. Standard 3-5 mm long x 2.5 mm wide, with an egg shaped limb. Wing 3 mm long. Keel 2-2.5 mm long
Stamens - 9 in a group and 1 alone.
Anthers -

Fruit:

Green-brown to black, hairless, flattened pod coiled into a disc shaped or cylindrical burr with 1.5 to 6 loose coils, 2-12 mm long x 3-8 mm diameter (without spines).Spines 2-4 mm long, spreading, curved or slightly hooked and often soft when mature. Occasionally spineless or warty. Valves have an obvious network pattern on the surface especially near the ends. Seam on the back of the pod is narrow with a furrow between it an each of the 2 parallel side veins. Pod usually has 3-6 seeds.

Seeds:

Brown, kidney shaped, 2-4 mm long, 1-2 seeds per coil of the pod.

Roots:

Taproot. Have nitrogen fixing nodules.

Key Characters:

Cotyledons oval shaped.
First leaf kidney shaped.
Older leaves trifoliate with the terminal leaflet on a longer petiolule than the side leaflets.
Square, hairless stems.
Yellow pea type flowers.
Disk shaped to cylindrical burr with 1.5 to 6 loose coils. Hooked, slender spines that are grooved near their base and 2-4 mm long. Network pattern on valves. Transverse nerves terminating in a nerve parallel to and on each side of the dorsal suture. Obvious furrows parallel to the dorsal suture on the pod. Peduncles are a similar length to the leaflet.
Kidney shaped seed.
Annual.

Biology:

Life cycle:

Annual. Germinates in autumn to winter and produces large amounts of palatable herbage in winter and spring. Flowers in spring and dies with the onset of summer drought and high temperatures.

Physiology:

Prefers high phosphate levels.
Can set seed in short growing season years.

Reproduction:

By seed.

Flowering times:

Spring in western NSW.
July to December in SA.
July to October in Perth.
Winter to spring in WA.

Seed Biology and Germination:

Produces hard or dormant seed.
Germinates from autumn to spring (561).

Vegetative Propagules:

None.

Hybrids:

Several varieties exist including var. vulgaris.
Some varieties have no spines or spines reduced to warts on the burr.
Var. brevispina has no spines.

Allelopathy:

Population Dynamics and Dispersal:

Mainly spread by burrs attaching to passing animals to distribute seed.

Origin and History:

Mediterranean. Europe.

Distribution:

ACT, NSW, NT, QLD, SA, TAS, VIC, WA.

Courtesy Australia's Virtual Herbarium.

Habitats:

Climate:

Temperate. Mediterranean.

Soil:

More abundant on heavy alkaline soils. Grows on a wide range of soils

Plant Associations:

In a range of communities from open grasslands to woodlands.

Significance:

Beneficial:

Important pasture species especially on the heavy alkaline soils.
Produces good quantities of palatable fodder over the winter to spring period.
Burrs provide a protein supplement over summer.
Fixes nitrogen.
Honey plant.

Detrimental:

Weed of crops, gardens, lawns, recreational areas and disturbed areas.
Causes vegetable fault in wool.

Toxicity:

Occasionally toxic causing photo sensitisation referred to as trefoil dermatitis, clover sickness or trifoliosis in sheep, cattle horses and pigs. Lambs including newly born ones are most affected. Mainly occurs on luxuriant growth during sunny weather in spring. May cause bloat in cattle.

Symptoms:

Dermatitis with no jaundice. Rarely fatal.
Bloat

Treatment:

Remove stock from infestation.

Legislation:

None.

Management and Control:

Thresholds:

In cropping situations, 10-40 plants/m2 are often worth controlling.

Eradication strategies:

Exclude stock to reduce dispersal of burrs.
Hand pull isolated plants in winter before flowering. For small infestations and grass dominant areas an annual application of 10 mL Tordon®75-D in 10 L water in early winter gives excellent control of existing plants and has residual activity to control later seedlings. In bushland, 25 mL of wetting agent plus 4 g of Lontrel®750 or 1 g of Logran® in 10 L water applied in early winter provides reasonably selective control. Metsulfuron(600g/kg) at 10 g/ha also provides good control but is less selective. Repeat annually for several years.
Plant tall growing perennial species to reduce re-invasion. It is relatively tolerant to glyphosate, grazing and mowing.

Herbicide resistance:

It is relatively tolerant to glyphosate.

Biological Control:

Related plants:

Barrel Medic. (M. truncatula)
Black Medic (M. lupulina)
Burr Medic (M. polymorpha)
Button Medic (M. orbicularis)
Calvary Medic (M. intertexta)
Cutleaf Medic (M. laciniata)
Disc Medic (M. tornata)
Gama Medic (M. rugosa)
Lucerne (M. falcata ssp. sativa)
Lucerne (M. sativa)
Small leaved Burr Medic (M. praecox)
Snail Medic (M. scutellata)
Spotted Medic (M. arabica)
Strand Medic (M. littoralis)
Woolly Burr Medic(M. minima)
Yellow Lucerne (M. falcata)

Plants of similar appearance:

Clovers (Trifolium species) usually have the central leaflet on a stalk the same length as the side leaflets.
Melilotus species
Oxalis species usually have a bitter taste.
Trefoils
It differs from native species which have leaves divided into 3 leaflets such as Gompholobium and Kennedia and in its flower and fruit characters.
Gompholobium marginatum has similar leaves but a loose cluster of few larger flowers and a stalked, somewhat brittle, broad pod.
Kennedia species usually have much larger leaflets and have much larger pink to red or orange flowers and a cylindric pod.

References:

Black, J.M. (1965). Flora of South Australia. (Government Printer, Adelaide, South Australia). P459. Diagrams.

Burbidge, N.T. and Gray, M. (1970). Flora of the Australian Capital Territory. (Australian National University Press, Canberra). P223. Diagram.

Cunningham, G.M., Mulham, W.E., Milthorpe, P.L. and Leigh, J.H. (1992). Plants of Western New South Wales. (Inkata Press, Melbourne). P402-3. Photo.

Everist, S.L. (1974). Poisonous Plants of Australia. (Angus and Robertson, Sydney). P470-471.

Hussey, B.M.J., Keighery, G.J., Cousens, R.D., Dodd, J. and Lloyd, S.G. (1997). Western Weeds. A guide to the weeds of Western Australia. (Plant Protection Society of Western Australia, Perth, Western Australia). P154. Photo.

Hyde-Wyatt, B.H. and Morris, D.I. (1975). Tasmanian weed handbook. (Tasmanian Department of Agriculture, Hobart, Tasmania). P104-105. Diagram.

Lamp, C. and Collet, F. (1990). A Field Guide to Weeds in Australia. (Inkata Press, Melbourne).

Lazarides, M. and Hince, B. (1993). CSIRO handbook of economic plants of Australia. (CSIRO, Melbourne). #806.12.

Marchant, N.G., Wheeler, J.R., Rye, B.L., Bennett, E.M., Lander, N.S. and Macfarlane, T.D. (1987). Flora of the Perth Region. (Western Australian Herbarium, Department of Agriculture, Western Australia). P284.

McBarron, E.J. (1983). Poisonous plants. (Inkata Press, Melbourne). P138-139. Diagram.

Wilding, J.L. et al. (1987). Crop weeds. (Inkata Press, Melbourne). P105. Diagrams. Photos.

Acknowledgments:

Collated by HerbiGuide. Phone 08 98444064 or www.herbiguide.com.au for more information.