Melilotus albus

Herbs usually biennial, rarely annual, 30–150(–260) cm. Stems erect or ascending. Leaves: stipules lanceolate-subulate to setaceous, 4–6(–10) mm, margins usually entire, sometimes toothed at base; leaflet blades narrowly oblong-obovate to suborbiculate-oblong, 10–24(–50) × 5–12(–15) mm, margins dentate. Racemes 40–80(–120)-flowered. Pedicels 1–1.5(–2) mm. Flowers 3.5–5(–6) mm; corolla white; ovary glabrous. Legumes obovoid, subglobose, or globose-ovoid, 3–5 mm, reticulate-veined, glabrous. Seeds 1 or 2(or 3), ovoid, (1.7–)2–2.5(–3.5) mm. 2n = 16.

Phenology: Flowering spring–fall.
Habitat: Grasslands, mixed forests, canyons, streamsides, riverbeds, lakeshores, waste places, roadsides.
Elevation: 0–2700 m.

Loading map...

Introduced; Greenland, St. Pierre and Miquelon, Alta., B.C., Man., N.B., Nfld. and Labr., N.W.T., N.S., Nunavut, Ont., P.E.I., Que., Sask., Yukon, Ala., Alaska, Ariz., Ark., Calif., Colo., Conn., Del., D.C., Fla., Ga., Idaho, Ill., Ind., Iowa, Kans., Ky., La., Maine, Md., Mass., Mich., Minn., Miss., Mo., Mont., Nebr., Nev., N.H., N.J., N.Mex., N.Y., N.C., N.Dak., Ohio, Okla., Oreg., Pa., R.I., S.C., S.Dak., Tenn., Tex., Utah, Vt., Va., Wash., W.Va., Wis., Wyo., Eurasia, introduced also in Mexico, West Indies, South America, Australia.

Discussion

Melilotus albus is extremely variable in Eurasia, and has been divided into many infraspecific taxa. It is the most important economic species in Melilotus, often grown as a crop, green manure, and honey plant, and posing a widespread weed problem.

Essentially all white-petaled Melilotus plants growing outside of cultivation in North America are M. albus; herbarium specimens often do not show the color well, sometimes resulting in misidentification, particularly between M. albus and M. officinalis. Aside from petal color, the species are quite similar. The venation areolae on the mature pods tend to differ: the raised venation ridges tend to form an irregular reticulation on the mature fruits of M. albus; they tend to form transverse areolae on the fruits of M. officinalis (S. J. Darbyshire and E. Small 2018). Although M. albus and M. officinalis are sometimes merged, there are very strong barriers to interbreeding between the two (G. T. Webster 1955; M. Maekawa et al. 1991), in addition to geographical and ecological differences, which justify their continued recognition as separate species.

P. Coulot and P. Rabaute (2013) included Melilotus albus in Trigonella sulcata (Desfontaines) Coulot & Rabaute (treated here as M. sulcatus). Most botanical literature incorrectly lists the authority for Melilotus albus as Desrousseaux in Lamarck instead of Medikus.

Selected References

None.

Lower Taxa