Yellow Sweet Clover, Melilotus officinalis, and White Sweet Clover, Melilotus albus

Sweet clover, genus Melilotus, is a group of some 23 species native to Eurasia, in the pea family, Fabaceae. Two of them, yellow sweet clover, Melilotus officinalis, and white sweet clover, Melilotus albus, are found all over North America. They are weedy and often quite aggressive, building up large populations quickly. But they add nitrogen to the soil, are good forage for livestock, are a source of honey for bees, and more. They have both supporters and detractors.

yellow sweet clover, Melilotus officinalis

white sweet clover Melilotus albus

The literature on yellow and white sweet clover is confusing, because more than 30 years ago, an expert called them a single species, with the name Melilotus officinalis, sweet clover. When not flowering, they are hard to tell apart. Both yellow and white sweet clover are very widespread. No expert has made a worldwide collection so there are many questions about how similar they might be in little-studied areas. Dried, both yellow and white flowers fade to cream-colored. However, they do not cross. Over the last 100 years repeated studies have tried to cross them, and they don't. For example, one experiment planted them together. Only 1 probable hybrid was found in 11,400 plants tested. If they were color variants of the same species, you'd expect thousands of hybrid plants. Recent genetic studies revealed they are quite different; DNA mapping puts them in different parts of the genus Melilotus. Thus, despite physical similarity, they are two separate species. (See Darbyshire and Small 2018 reference.) There are other examples of cryptic species of animals and plants, where the two species never cross, even though they look identical to humans. Biologists don't like it, but Nature didn't ask us. I will follow Darbyshire and Small and the Flora of Colorado, and call them two species. Note that the USDA Plants data base lists only one species, Melilotus officinalis.

Both species are from Eurasia and are now all over the world, welcomed by some and treated as weeds by others. White sweet clover is the one more commonly planted as a crop, for forage or for bees or as a medicinal. Yellow sweet clover is less often planted so it more often seen as a weed problem.

A lot of yellow sweet clover, Colorado

The name Melilotus is from Greek, meli for honey, lotus a leguminous plant; the species epithet officinalis means "of the office" that is, the one the doctor prescribed; albus means white. 

Botanical geek trivia: Older works, including the very important Gray's Manual of Botany, use Melilotus alba not Melilotus albus. Scientific names treat the genus name as a noun, the species epithet as an adjective that must match the gender of the noun. Latin nouns ending in -us are generally masculline, the ending -a indicates a feminine noun, and -um a neuter noun. Endings for adjectives are typically -us masculine, -a feminine, and -um neuter, though there are a number of other possible endings. Languages with genders frequently have a few words that don't conform, which might, for example, have a typical masculine ending but in fact be feminine and so take feminine adjectives. (I've been studying Spanish, which has some of those). That occurred in Latin too. A variety of tree scientific names are feminine but end in -us, for example Cornus (dogwoods) and Pinus (pines) so Cornus sericea and Pinus ponderosa are correct. Apparently scholars of the early 20th century considered Melilotus as a feminine noun. However, the current international code of nomenclature for plants specifically states that Melilotus and Lotus are masculine. So Melilotus officinalis and Melilotus albus are the correct forms. 

The common name sweet clover links it to other clovers, which it resembles, though it is more closely related to alfalfa. I have always thought "sweet" referred to the scent of the flowers, which is strong and distinctive when you walk through a patch of sweet clover in flower. Online sources point to the scent of the crushed leaves; they release coumarin which smells sugary. Modern sources almost all use the common name sweet clover, but older English works call it melilot. 

yellow sweet clover

Sweet clovers are good forage for cattle and other livestock, if part of a diverse diet. Coumarins slow blood clotting, so livestock should eat sweet clovers in moderation. Cultivated sweet clover varieties have been bred to have less coumarin.

They produce a rich nectar which honey bees make into clover honey, and their flowers attract and feed many other nectar-feeders, such as bees, butterflies, flies, as well. 

Sweet clovers add nitrogen to the soil and can be cut and plowed in to raise the nitrogen and organic content of the soil. They are sometimes planted as a cover crop to stabilize the soil while slower-growing plants get established.

The small nutty seeds are eaten by songbirds and small mammals.

In North America, and elsewhere outside their native range, the sweet clovers are aggressive, taking over waste areas, especially those low in nitrogen where their nitrogen-fixing capacity gives them an edge. To people who wanted other plants in that area, sweet clovers are invasive weeds. 

dense stand of yellow sweet clover, Melilotus officinalis

Sweet clovers have a long history as medicines. They were used as a poultice to soften scar tissue and speed healing. Sweet clover tea treated upset stomachs and flatulence. German Commission E tested them and found sweet clovers effective in healing blunt injuries, treating hemorrhoids, and aiding chronic venous insufficiency such as pain and heaviness in the legs. The coumarins in the leaves are blood thinners and as far as I can tell, sweet clover plants can differ greatly in the concentration of coumarins, so working with reliable sources of plants, rather than foraging, seems prudent. And sweet clovers as medicines are counter-indicated for anyone with blood clotting problems.

Sweet clover's pleasant, "vanilla-y" scent carries over into a pleasant tea. Dried, the plants were used as room fresheners, the scent reportedly serving as an antidote for melancholy. Historically they were also used with stored clothing, to provide the appealing scent and to protect furs from moths. 

This one showed up uninvited in my yard. I
weeded it out. Now I'm sorry. At minimum, it would
make a pretty, sweet-smelling bouquet.

Mostly I see them in large numbers on the roadside and think of sweet clovers as weeds. Clearly, it would be better to think of them as a plant introduced to North America that, overall, does more good than harm. Try smelling a bouquet of sweet clover!

Comments and corrections welcome

References

Ackerfield, J. 2020. Flora of Colorado. 2nd edition. BRIT Press, Fort Worth, Texas. 

Darbyshire, S. and E. Small. 2018. Are Melilotus albus and Melilotus officinalis conspecifics? Genetic Research and Crop Evolution. 65: 1571-1580.

Fernald, M.L. 1970. Grays Manal of Botany. 8th edition. D. Van Nostrand Company. New York, New York.

Grieve, M. 1931. A Modern Herbal. Dover Publications, New York. online  (as melilot). Accessed 5/22/25.

Moore, M. 2003. Medicinal Plants of the West. revised ed. Museum of New Mexico Press. Santa Fe, New Mexico. 

RXlist. Sweet clover. link Accessed 5/22/25.

Thomson Healthcare, Inc. 2007. PDR for Herbal Medicine. 4th ed. Thomson Publishing, Montvale, New Jersey. 

Turland, N. J. (chair) 2018. International Code for Nomenclature for algae, fungi and plants (ShenZhen Code). International Association for Plant Taxonomy. (VIII, 2. 2.1, Note 2) link Accessed 5/20/25.

Kathy Keeler

A Wandering Botanist

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