Medicago polymorpha
Medicago rigidula
bur medic, bur-clover, bur-clover or medic, burr medic, California burclover, smooth medic, tooth bur clover, tooth medic, tooth medick
rigid or Tifton bur (burr) medic, Tifton burclover, Tifton medick
procumbent, decumbent, or ascending.
procumbent to ascending.
blades obovate, obcordate, or cuneate, 8–20 × 7–18(–20) mm, margins usually serrate, rarely laciniate, on distal 1/3–1/2.
blades cuneate to obovate, (4–)6–12 × (3–)4–8 mm, margins serrate on distal 1/2.
(1 or)2–6(–10)-flowered, racemes.
1–3(–6)-flowered, racemes.
3.5–6 mm;
calyx sparsely pubescent, hairs eglandular, lobes equal to tube;
corolla yellow, usually less than 2 times length of calyx.
(3–)4–6(–8) mm;
calyx pubescent, hairs eglandular and/or glandular, lobes shorter to longer than calyx length;
corolla yellow, less than 2 times length of calyx.
with 1.5–7 coils, discoid, short to long cylindrical, or conical-truncate, 2–12 × 4–10 mm, usually glabrous, margin usually prickly, sometimes tuberculate or prickleless, prickles, when present, often relatively thin and flexible, base 2-rooted, 1 root arising in dorsal suture, other in submarginal vein;
faces moderately soft, sometimes very hard at maturity, coil face with transverse veins anastomosing in outer part of coil before entering lateral vein near coil edge.
with (4–)5–6.5(–7.5) coils, coils weakly to strongly adpressed, usually ovoid, sometimes cylindrical, discoid, or spherical, 5–10(–12) × 5–10(–15) mm, usually pubescent with eglandular and gland-tipped hairs, evident only when young, when glandular, often producing velvety appearance, rarely glabrous, margin prickly, tuberculate, or prickleless, prickles, when present, at different angles to plane of coil, very stocky and difficult to bend, base often round, 2 roots often apparent at maturity;
faces very hard at maturity, coil face with strongly curved radial veins anastomosing somewhat towards coil periphery, veins obscure at maturity from developing spongy tissue.
2–12, light yellow to brownish, reniform, 2–4 × 1.5–2.2 mm;
radicle 1/2 seed length.
yellow to yellow-brown, reniform, (2.5–)3–4(–4.5) × (1.3–)1.5–2(–2.5) mm;
radicle 1/2, or slightly less, seed length.
margins laciniate.
margins dentate to laciniate.
= 14, 16.
= 14, 16.
Medicago polymorpha
Medicago rigidula
Medicago polymorpha is one of the more important annual medics that have been developed for use as pasture forage for dry, hot environments. About a dozen cultivars have been bred.
Medicago polymorpha is the most likely species of the genus to be confused with other species. The fruits are easily misidentified as one of the hard-fruited Medicago (M. rigidula, M. truncatula, M. turbinata), but are fairly similar to those of certain of the soft-fruited taxa, particularly M. laciniata and M. minima, two species that are also quite common as weeds. The fruit coil faces of both of the latter species have distal veinless areas. The coil face of M. polymorpha has quite reticulate venation, whereas that of M. laciniata has notably S-shaped radial veins that anastomose little. Medicago minima is a quite hairy plant, whereas M. polymorpha is almost always glabrous.
(Discussion copyrighted by Flora of North America; reprinted with permission.)
Medicago rigidula has been sown for forage only to a limited extent. There are a few forage cultivars, including ‘Laramie’, a self-regenerating pasture species for the Central High Plains of the United States.
The European and African populations of this species complex have been segregated as Medicago rigiduloides E. Small, based particularly on pollen morphology and fruit characters (E. Small et al. 1990). Additional studies confirming separation of these taxa are needed (D. C. Heft and R. W. Groose, http://www.naaic.org/Publications/ 1996Proc/poster_session.htm), before determining their applicability to the plants in the flora area.
(Discussion copyrighted by Flora of North America; reprinted with permission.)
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