Kingdom: Plantae
(unranked): Angiosperms
(unranked): Eudicots
(unranked): Rosids
Order: Fabales
Family: Fabaceae
Subfamily: Faboideae
Genus: Medicago
Species: M. polymorpha
Binomial name: Medicago polymorpha
Common names: Burclover, California burclover, toothed bur clover, Toothed medick, Burr medic.
Medicagopolymorpha is an annual, broadleaf plant species of the genus Medicago. It is native to the Mediterranean basin but is found throughout the world. It forms a symbiotic relationship with the bacterium Sinorhizobium medicae, which is capable of nitrogen fixation. It inhabits agricultural land, roadsides and other disturbed areas and lawns.
Medicago polymorpha when fully grown has reddish-purple coloured stems up to 60 cm long and they usually sprawl along the ground and will climb over other vegetation. The stems often root at the nodes; adult plants, and even young plants that have been able to grow for a few weeks undisturbed can be very difficult to pull out, leaving behind taproots and a network of plant pieces when pulled. It becomes invasive and displaces more desirable vegetation.
The first true leaf is rounded. Later leaves will be tripartite, with a characteristic clover-like shape, appearing alternately on the stems. Leaflets have slightly serrated edges.
The tiny yellow flowers (3–6 mm long) are clover-like and cluster into flower heads of 2 to 10 flowers at the stem tips. Flowering occurs in spring. After flowering when the leaves turn yellow, tiny green (7 mm across) seed pods develop. These are coiled tightly > 6 times. The pods have rows of prickles on the outside edge. They start out green and relatively soft, but quickly turn brown and hard. Inside each pod (burr) there are several seeds.
The hooked prickles on the seed pods cling to the clothing or fur of any species that pass near it, thus facilitating the geographic spread of this species. They can be quite difficult to remove and when attached to sheep they reduce the value of the wool.
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The curled, dried seed pod (a burr)
Thanks to Wikipedia for text and information: https://creativecommons.org/licenses/by-sa/3.0/
