Medicago lupulina is a summer annual or perennial plant usually considered a weed. It has a tap root. Like other legumes, it has three leaflets; its center leaflet is on a separate petiole

Petiole (botany)

In botany, the petiole is the stalk attaching the leaf blade to the stem. The petiole usually has the same internal structure as the stem. Outgrowths appearing on each side of the petiole are called stipules. Leaves lacking a petiole are called sessile, or clasping when they partly surround the...

. As with other legumes, nitrogen-fixing bacteria

Bacteria

Bacteria are a large domain of prokaryotic microorganisms. Typically a few micrometres in length, bacteria have a wide range of shapes, ranging from spheres to rods and spirals...

, known as rhizobia

Rhizobia

Rhizobia are soil bacteria that fix nitrogen after becoming established inside root nodules of legumes . Rhizobia require a plant host; they cannot independently fix nitrogen...

, are found in nodules on the roots.

Description

Medicago lupulina is an annual or bi-annual plant, sometimes long-lived thanks to adventitious buds on the roots. The plant measures from 15 to 60 cm in height, with fine stems often lying flat at the beginning of growth and later erecting. The nodes bear three leaves, carried by a long petiole and have oval leaflets, partially toothed towards the tip. This species has very small yellow flowers are grouped in tight bunches. The fruit is a pod that does not open upon maturation, of a little arched form and bearing a single seed.

Note: it is sometimes confused with other plants that have small leaves divided into three leaflet

Leaflet

A leaflet in botany is a part of a compound leaf. A leaflet may resemble an entire leaf, but it is not borne on a stem as a leaf is, but rather on a vein of the whole leaf. Compound leaves are common in many plant families...

s and small yellow flowers, such as members of:

• the clover
  Clover
  Clover , or trefoil, is a genus of about 300 species of plants in the leguminous pea family Fabaceae. The genus has a cosmopolitan distribution; the highest diversity is found in the temperate Northern Hemisphere, but many species also occur in South America and Africa, including at high altitudes...
  
   genus, like Hop Trefoil and Lesser Hop Trefoil
  Trifolium dubium
  Trifolium dubium, the Lesser Hop Trefoil or suckling clover is a plant in the family Fabaceae. This species is generally accepted as the primary plant to represent the traditional Irish Shamrock....
  
  
• the false shamrock
  Oxalis
  Oxalis is by far the largest genus in the wood-sorrel family Oxalidaceae: of the approximately 900 known species in the Oxalidaceae, 800 belong here...
  
   genus, like Yellow Woodsorrel
  Oxalis stricta
  Oxalis stricta, called the common yellow woodsorrel , common yellow oxalis, upright yellow-sorrel, lemon clover, or more ambiguously and informally "sourgrass" or "pickle plant", is an herbaceous plant native to North America, parts of Eurasia, and has a rare introduction in Britain...
  
  

Distribution

This plant can be seen through the old world: all of Europe, a great part of Asia, including China, Korea and Taiwan, as well as the Indian sub-continent, North Africa, the islands of the Atlantic (the Canaries, Madeira) and throughout the United States, including Hawaii.

It thrives in dry limestone grounds and coastal sand dunes, where it suffers less competition from the other plants. It is relatively cold resistant and can be seen in mountains up to 1800m.

Use

Medicago lupulina is sometimes used as a fodder

Fodder

Fodder or animal feed is any agricultural foodstuff used specifically to feed domesticated livestock such as cattle, goats, sheep, horses, chickens and pigs. Most animal feed is from plants but some is of animal origin...

 plant. While being of good value, it isn't a very productive fodder. It is sometimes used in the composition of artificial meadows, especially when implanted in dry lands. It is a common sight in natural pastures. It is also one of the flowers that can be used to create honey

Honey

Honey is a sweet food made by bees using nectar from flowers. The variety produced by honey bees is the one most commonly referred to and is the type of honey collected by beekeepers and consumed by humans...

.

External links

• Entry in the Linnean herbarium
• A mention in 1866 from the Correspondence of Charles Darwin
  Correspondence of Charles Darwin
  The British naturalist Charles Darwin had correspondence with numerous other luminaries of his age and members of his family. These have provided many insights about the nineteenth century, from scientific exploration and travel to religious debate and discussion...
  
  : "Several years ago I protected Medicago lupulina from insects, & its fertility was much impaired, but not wholly prevented."
• WeedAlert.com's listing for Medicago lupulina
• Effect of Black Medic Cover Crop on N Supplying Power of Prairie Soils
• Wikispecies entry