Plant relationship: Most sources, including USDA and the Checklist of the Vascular Plants of Minnesota of the U of M, consider M. alba to be simply a color variant of Yellow Sweet Clover, M. officinalis. Except for the color of the flowers, both are erect annual to biennial invasive plants. Stems are green, ridged or slightly angled, upright, and can be from 1 to 5 feet high.
Leaves are 3-parted with oblong leaflets with the side leaflets on very short stalks and the middle leaflet on a stalk about 5x longer. Leaf edges have teeth-like serrations. At the base of the 1/2 inch or longer stalk of the compound leaf is a pair of very small pointed stipules.
The flowers are 5-parted, small, 1/8 to 1/4 inches long, stalked, and appear in 4 inch tall, long-stalked racemes, springing from the leaf axils of the upper leaves of the many widely branching stems. On the flower raceme flowers tend to be loosely arranged. As a biennial (usually the case in Minnesota) the flowers appear on 2nd year plants. The flower corolla forms a tube in typical pea flower fashion. At the outer end the corolla separates into 5 petals with the large banner (or standard) petal curving upward, flanked by two forward projecting laterals that are slightly under and much longer than the two keel petals which form the center of the flower. In many pea family flowers the laterals enclose the keel. Inside the keel petals are the reproductive parts, usually 10 stamens and a single slightly curved style. The green calyx is about 1/3 to 1/2 as long as the corolla and has 5 pointed teeth of unequal length. The entire flower curves upward slightly from its drooping position.
Seeds are contained in a small flattened seedpod, smooth or slightly patterned, containing 1 to 2 seeds, each 2 to 3 mm long. These are viable in the ground for 30 years.
Habitat: Melilotus develops a deep tap root and grows best in full sun but tolerates some shade. Soil conditions can be poor to good with adequate moisture, but tolerates slightly dry conditions. Roadsides and disturbed soil are thus the ideal places to find this plant. It is nitrogen fixing however.
Names: The genus name Melilotus comes from two Greek words Meli meaning "honey" and lotos, meaning "lotus", all referring to the plant having abundant sweetness and being a favorite of bees. The species names are - alba, meaning 'white' and officinalis meaning 'sold in shops;' a name which is used when plants have some medicinal qualities, real or supposed, and herbalists made the plant available in their shops. See notes below. The author name for the plant classification of White Sweet Clover, ‘Medikus’ is for Friedrich Kasimir Medikus (1738-1808) German botanist, director of the University of Heidelberg and curator of the botanical garden at Mannheim and for Yellow Sweet Clover, the first to classify was '(L.)' which refers to Carl Linnaeus (1707-1778), Swedish botanist and the developer of the binomial nomenclature of modern taxonomy. His work was updated by ‘Lam.’ which is for Jean-Baptiste Lamarck (1744-1829) French naturalist and biologist, an early proponent of evolution who among other things, published the 3 volume Flore francaise. He is best known for his theory of the inheritance of acquired characteristics.
Above: White Sweet Clover. Below: Yellow Sweet Clover (Melilotus officinalis (L.) Lam.). Several differences between the yellow and the white have been noted: Yellow is shorter and blooms slightly earlier. Otherwise there are no noticeable differences. The flowers of sweet clover are loosely arranged on the raceme and each one tends to droop downward on its short stalk. Note the pointed teeth on the green calyx.
Below: 1st photo - Yellow Sweet Clover - The typical 3-parted oblong leaflets with the middle leaflet on a stalk that is about 5x longer than that of the side leaflets. 2nd photo - leaf of White Sweet Clover.
Below: 1st photo - Where the leaf stalk meets the stem are a pair of very small pointed stipules.
Below: 1st photo - Detail of the 5 petals. Note the two lateral petals, instead of enclosing the keel, are partially under and much longer than the two keel petals in the center of the flower. 2nd photo - when the keel petals fall away the stamens and the longer curved style are visible.
Below: 1st photo - Seed pods of Yellow Sweet Clover, note the slight reticulation (vein network) on both the green pods and the mature pods. 2nd photo - Seed pods of White Sweet Clover, with the reticulation quite visible. Each pod contains 1 to 2 smooth tan colored seeds.
Below: The root is a deeply penetrating branching taproot with fibrous feeder roots. Very difficult to remove on stout plants.
Notes: White and Yellow Sweet Clover are non-native plants, now naturalized all over the United States and found in most counties of Minnesota. Although Eloise Butler did not catalogue it in her first Garden records, she noted planting it on July 19, 1922 with plants she brought in from Glenwood Park (which partially surrounded the Garden). It was listed on Martha Crone's 1951 Garden Census. It is listed as a non-native invasive in most states, including Minnesota. The plant arrived in the United States from Europe in the 1600's. Wildlife however, use parts of the plant in their diet, particularly browsers. Studies have found that mule deer make up 70% of their diet with Sweet Clover in the summer and fall. Cattle however, do not like it due to the bitter taste of the chemical coumarin found in the plant, but they become used to it and then include it in their diet. Realization of this fact, caused it to be planted extensively on range land in the west for the browsing cattle herds. As it escaped to the roadsides and other places where it was not wanted, it became known as 'weedy'. In the western states in the national parks and monuments it has taken over great swaths of roadside and fields.
Lore: The plant has some very early history of medicinal use as an emollient and digestive. The entire plant would be dried and then in solution would come out the active ingredient, Coumarin. While the plant was not widely found in Great Britain, Gerard (Ref. 6a) did write about it and in regards the plant's invasive character he had this to say:
"For certainty no part of the world doth enjoy so great plenty thereof as England and especially Essex, for I have seen between Sudbury in Suffolke and Clare in Essex and from Clare to Hessingham very many acres of earable pasture overgrowne with the same; in so much that it doth not only spoil their land, but the corn also, as Cockle or Darnel and is a weed that generally spreadeth over that corner of the shire." John Gerard (1545-1612) Gerard's Herbal.
References: Plant characteristics are generally from sources 1A, 32, W2, W3, W7 & W8 plus others as specifically applied. Distribution principally from W1, W2 and 28C. Planting history generally from 1, 4 & 4a. Other sources by specific reference. See Reference List for details.
Identification booklet for most of the flowering forbs and small flowering shrubs of the Eloise Butler Wildflower Garden. Details Here.
Friends of the Wild Flower Garden, Inc. Text and photos are by G. D. Bebeau unless otherwise credited. "www.friendsofthewildflowergarden.org"