T.E.R:R.A.I.N - Taranaki Educational Resource: Research, Analysis and Information Network


Melilotus officinalis (Yellow sweetclover)

Kingdom: Plantae
(unranked): Angiosperms
(unranked): Eudicots
(unranked): Rosids
Order: Fabales
Family: Fabaceae
Subfamily: Faboideae
Tribe: Trifolieae
Genus: Melilotus
Species: M. officinalis
Binomial name: Melilotus officinalis
Common names: Yellow sweetclover, Yellow melilot, Ribbed melilot

Melilotus officinalis (Yellow sweetclover) is a species of legume native to Eurasia and was introduced to New Zealand. It is a a biennial and sometimes annual or short-lived perennial that in New Zealand it inhabits dry waste areas and in waste coastal areas. In New Zealand it is found in Gisborne, Palmerston North, Wellington, Blenheim, Canterbury and Gore.
Yellow sweetclover is an erect plant and can grow to about 2 m tall with spreading branches. Stems become somewhat woody at the base, especially in the second year. Leaves are fully divided into three leaflets that have a serrated margin. . Leaflets are egg shaped to oblong and mostly 1–2.5 cm long. The middle leaflet has a short stalk. Leaves are alternate to one another along the stem.
Small, yellow, sweetly fragrant, pea like, short-stalked flowers bloom during spring and summer. They are in 3–12 cm long clusters along the end of each flowering stem. They produce seeds in a hairless oval-shaped pod (3–5 mm long) that has a sharply ridged or veined, light brown surface. The pods hang from downward bent stalks. Each pod typically containing one seed that are somewhat oval, smooth, yellowish green to orange-tan in colour and sometimes they have purplish or brown spots. Seeds can be viable for up to 30 years. The plants have large taproots and tend to grow in groups. Plants have a characteristic sweet odour.

Yellow sweetclover can a problematic weed because the leaves and flower buds contain a low level toxicant called coumarin. If sweet clover hay is poorly cured, it can develop mould that converts the coumarin to a more toxic compound called dicoumarin which is a powerful anticoagulant toxin. Animals feeding on mouldy sweetclover hay can lead to an often, fatal hemorrhaging disorder called “sweetclover poisoning”. This has not been reported in New Zealand.
In the chemical industry, dicoumarin is extracted from the plant to produce rodenticides