Melilotus alba, white sweetclover

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Intermountain Flora
Closely resembling the preceding in habit, foliage, and inflorescence, but the petals white (ochroleucous when dried), often shorter and more evidentally graduated, the banner (3) 3.5-5 (6) mm long, distinctly longer than wings; pod subsymmetrically ellipsoid, more abruptly contracted at base, 2.5-3 x 1.5-2 mm, the valves finely reticulate, all venules about equally strong; ovules only 2-4; seed of M. officinalis but never mottled.

Cronquist, A., Holmgren, A.H., Holmgren, N.H., Reveal, J.L., and Holmgren, P.K. (1989) "Intermountain Flora" pg. 234, vol. 3 part B, The New York Botanical Garden New York.