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Medicago
See list of 11 species in this genusThough flowering specimens possess many good characters on which to base identifications, fruits are generally necessary for identification of some of the rarer species of Medicago that have been introduced to New England. Reference: Small and Jomphe (1989).
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1a. Inflorescence with 1 or 2 (–3) flowers; legume (30–) 40–100 mm long, unarmed, merely curved
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1b. Inflorescence with (1–) 2–50 flowers; legume 1–10 mm long, armed with thin prickles or unarmed, curved to coiled up to 7 times (rarely straight in M. falcata and M. lupulina)
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2a. Corollas 6–12 mm long, blue-purple to purple or rarely yellow; legumes unarmed; plants perennial
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3a. Corollas blue-purple to purple, usually 8–11 mm long; legumes coiled (1–) 2–3 times; stems erect to ascending
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3b. Corollas yellow, usually 5–8 mm long; legumes falcate-curved (rarely straight or partly coiled); stems prostrate to erect
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2b. Corollas 2–5 (–7) mm long, yellow; legumes armed with thin prickles (always unarmed in M. lupulina, rarely unarmed in M. rigidula) [Fig. 645];
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4a. Legume reniform-curved or slightly spiraled near the apex, without prickles [Fig. 646], with a single seed; inflorescence with (10–) 14–24 (–50) flowers
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4b. Legume 2- to 7-times spiral-coiled, with thin prickles (prickles rarely lacking in M. rigidula), with several seeds; inflorescence with (1–) 2–5 (–8) flowers
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5a. Legume in a very tight spiral, extremely hard-walled, usually glandular-puberulent, the young legume concealed within the calyx when the petals drop; prickles of legume (when present) stocky, firm, ± round at the base
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5b. Legume in a somewhat tight spiral, soft-walled, glabrous or pubescent with eglandular hairs (sometimes glandular in M. minima, but that species with small fruits 3–5 mm in diameter), the young legume projecting sideways from the calyx when the petals drop; prickles of legume relatively thin, flexible, with 2 roots, 1 root arising in the dorsal surture, the other root arising in the submarginal vein
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6a. Faces of the fruit coils lacking a reticulum of veins over much of the surface; prickles of legume tending to slant toward the base of the fruit
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6b. Faces of the fruit coils with a reticulum of bold veins over much of the surface (the veins sparingly branched in M. laciniata, but still evident); prickles of legume tending to project outward from fruit (i.e., parallel with fruit coil)
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7a. Leaflets broad-obovate to broad-obcordate, 0.7–1.1 times as long as wide, usually with a dark blotch or mottles on the adaxial surface; prickles on legume usually curved and somewhat conforming to the outline of the fruit [Fig. 645]
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7b. Leaflets elliptic to obovate or obcordate, 1–2 (–2.5) times as long as wide, without dark mottles; prickles on legume relatively straight (except near apex of fruit), diverging from outline of fruit
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8a. Stipules entire or slightly dentate; legumes sparsely pubescent; stems moderately to densely villous
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8b. Stipules lacerate; legumes usually glabrous; stems glabrous or sparsely pubescent
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9a. Corolla 2–3 (–4) mm long; coils of fruit loosely appressed to each other (i.e., spaces evident between the coils when the fruit is viewed on edge); margin of fruit coils very broad
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9b. Corolla (3–) 4–8 mm long; coils of fruit moderately to tightly appressed to each other; margin of fruit coils narrow
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10a. Leaflets 8–20 mm long, apically denticulate; legumes 4–8 (–10) mm in diameter, with transverse veins that anastomose toward the margins, with the submarginal veins separated from the marginal vein by a deep groove that is visible when the legume is viewed on edge
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10b. Leaflets 5–10 (–12) mm long, commonly laciniately toothed; legumes 2.5–5 mm in diameter, with tranverse veins that are merely sparingly branched toward the margins, with the submarginal veins separated from the marginal vein by a narrow groove that is ± not visible when the legume is viewed on edge
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Each photo represents one species in this genus.