Fabaceae: Melilotus officinalis
Family Name
Fabaceae
Common Name
Yellow sweet clover
Description
Melilotus officinalis is a biennial or short-lived perennial herbaceous plant growing 30 to 150 cm tall. It has a deep taproot and a fibrous root system capable of fixing nitrogen. The stems are erect, slender, and often branched, with a smooth to sparsely hairy surface. Leaves are alternate and trifoliate, with three oval to obovate leaflets measuring about 1.5 to 4 cm long and 1 to 2 cm wide; leaflets have finely serrated margins and a smooth to slightly hairy surface. The leaflets are petiolulate with short stalks about 2 to 5 mm long, and stipules are small and lanceolate at the base of the leaf stalks. The inflorescence is a long, slender raceme of small, fragrant, bright yellow pea-shaped flowers blooming from late spring to early fall (May–September). Each flower is subtended by a calyx of five sepals fused at the base into a tubular cup about 3 to 6 mm long, with five pointed lobes that are lanceolate and often hairy. Flowers measure about 6 to 9 mm long. The corolla’s standard petal is broadly ovate, approximately 6 to 8 mm long and 4 to 6 mm wide; the wing petals are about 5 to 7 mm long and 2 to 3 mm wide; the keel, formed by two fused petals, is about 5 to 8 mm long and 2 to 3 mm wide. Flowers have ten stamens, nine of which are fused, and a superior ovary. The fruit is a small pod about 4 to 8 mm long containing one to two seeds. Yellow sweet clover is native to Eurasia but widely naturalized and sometimes invasive in North America, including South Dakota, commonly found in roadsides, fields, and disturbed habitats statewide.
Additional Notes
Yellow Sweet Clover can be highly invasive, crowding out native plant species. It is cultivated for its soil improvement qualities, forage use, and nectar for pollinators. It becomes woody later in the growing season and loses much of its forage value