Trefoil, or Clover, in botany: A genus of plants belonging to the class of diadelphia, and order of decandra; and in the natural system ranging under the 32d order, Papilionaceae. The flowers are generally in round heads; the pod is scarcely longer than the calyx, univalve, not opening, deciduous. The leaves are three together. According to Murray's edition of Linnaeus, there are 46 species; of which 17 are natives of Britain. We shall describe some of the most remarkable of these:

1. Meliloti officinalis, or melilot, has naked racemose pods, stipitate, wrinkly, and acute, with an erect stalk. It grows in corn-fields and by the way-sides, but not common. The stalk is erect, firm, striated, branched, and two or three feet high; the leaves ternate, smooth, obtuse oval, and serrated; the flowers are small, yellow, pendulous, and grow in long close spikes at the tops of the branches; the pod is very short, turgid, transversely wrinkled, pendulous, and contains either one or two seeds. The plant has a very peculiar strong scent, and disagreeable, bitter, acid taste, but such, however, as is not disagreeable to cattle. The flowers are sweet-scented. It has generally been esteemed emollient and digestive, and been used in fomentations and cataplasms, particularly in the plaster employed in dressing blisters; but is now laid aside, as its quality is found to be rather acid and irritating than emollient or resolvent. It communicates a most loathsome flavour to wheat and other grain, so as to render it unfit for making bread. It grows in corn-fields.

2. Trifolium repens, white creeping trefoil, or Dutch clover, has a creeping stalk, its flower gathered into an umbellate head, and its pods tetrapermous. It is very common in fields and pastures. It is well known to be excellent fodder for cattle; and the leaves are a good rustic hygrometer, as they are always relaxed and flaccid in dry weather, but erect in moist or rainy.

3. Trifolium pratense, purple or red clover, is distinguished by dense spikes, unequal corollas, by bearded stipulas, ascending stalks, and by the calyx having four equal teeth. This is the botanical description of this species given by Mr Afzelius, who, in a paper of the first volume of the Linnean Transactions, has been at much pains to remove three species of the trifolium from the confusion in which they have been long involved; namely, the pratense, medium, and alpestris. The red clover is common in meadows and pastures, and is the species which is generally cultivated as food for cattle. It abounds in every part of Europe, in North America, and even in Siberia. It delights most in rich, moist, and sunny places; yet flourishes in dry, barren, and shady places. For an account of the mode of cultivating it, see Agriculture, p. 177.

4. Alpestris, long-leaved purple trefoil, or mountain clover, is thus characterized by Mr Afzelius. The spikes are dense; the corollas somewhat equal; the stipulas are bristly and divergent; the leaflets lanceolate; the stalks stiff, straight, and very simple. It grows in dry, mountainous, woody places, in Hungary, Austria, and Bohemia, &c.; but is not said by Mr Afzelius to be a native of Britain.

5. The medium, according to Mr Afzelius, has also been confounded with the two species last mentioned; but it is to be distinguished from them by having loose spikes, corollas somewhat equal, stipulas subulate and connivent, and stalks flexuous and branched. It is found in dry elevated situations, especially among shrubs, or in woods where the soil is chalky or clay, in England, Scotland, Sweden, Denmark, &c.

For a botanical description of the other species of the trifolium, see Lightfoot's Flora Scotiae, Berkenhout's Synopsis of the Natural History of Great Britain and Ireland, and Withering's Botanical Arrangements.