Medicago sativa L. (alfalfa)
Pl. 402 h–j; Map 1783
Plants long-lived perennials, with deep
taproots below a knobby or sometimes short-branched, woody caudex. Stems
30–60(–90) cm long, erect to loosely ascending, sometimes from a spreading
base, sometimes clump-forming, glabrous or finely hairy. Petioles mostly 10–50
mm long (those of the uppermost leaves sometimes shorter). Stipules 6–18 mm
long, the margins entire or shallowly toothed toward the base, fused to the
petiole toward the base. Leaflets 10–32 mm long, 2–12 mm wide, oblanceolate to
elliptic or narrowly obovate, rounded to minutely notched at the tip, the
midvein often extended as a short, narrowly triangular, sharply pointed tooth
at the very tip, the surfaces glabrous or sparsely hairy, the upper surface
lacking a red or purple spot. Inflorescences dense racemes, appearing as headlike
clusters, more or less globose to oblong-ovoid or short-cylindric at flowering,
with 10–30 flowers, often extending beyond the subtending leaves, the stalk
10–30 mm long. Calyces with the tube 1.5–2.0 mm long, the lobes 2.5–3.5 mm
long. Corollas 6–11 mm long, blue to purple, rarely yellow (white, lavender, or
variegated elsewhere). Filaments with the fused portion 4–5 mm long, the free
portion 1–2 mm long. Fruits 4–6(–10) mm long, longer than wide, strongly curved
to loosely coiled 1–3 turns, smooth, not prickly, glabrous or finely hairy,
yellow to brown, 3–8-seeded. 2n=16,
32. May–September.
Introduced, scattered nearly throughout
the state (native of Europe, Asia; introduced nearly throughout the U.S.
[including Alaska, Hawaii], Canada, and elsewhere in the world). Banks of
streams and rivers, marshes, and tops of bluffs; also pastures, levees,
railroads, roadsides, and open, disturbed areas.
The deep and strong taproots enable
this species to withstand drought and to grow in dry, rocky habitats. Once
established, it can persist for a long time. Medicago sativa is perhaps the oldest and most important cultivated
forage crop (Quiros and Bauchan, 1988). Alfalfa was cultivated long before
recorded history began in the area now known as Iran. Its development as a crop
was tied to the increasing use of horses for transport and warfare. Early Roman
writers reported that it was introduced into Greece as early as 490 B.C. by
invading Mede and Persian armies. It was later taken to Italy and other
European countries. Early attempts during the 1700s to grow alfalfa by
colonists in the eastern portion of what is now the United States apparently
were unsuccessful (Oakley and Westover, 1922; Barnes et al., 1988). However,
the plant was successfully introduced into California from Chile by the Spanish
during the Gold Rush era of the 1850s (Oakley and Westover, 1922; Barnes et
al., 1988).
Yellow flowered specimens of M. sativa are occasionally collected in
Missouri and have been difficult to name. The M. sativa polyploid complex consists of a series of diploid (2n=16)
taxa and various polyploid derivatives. These have variously been treated as
several closely related species (Lesins and Lesins, 1979; Isely, 1998) or
mostly as a series of subspecies of M.
sativa (E. Small and Jomphe, 1989). Among these, cultivated alfalfa (ssp. sativa) is thought to have arisen as an
autotetraploid (2n=32) derivative from a wild, blue-flowered, somewhat smaller,
diploid taxon known as ssp. caerulea
(Less. ex Ledeb.) Schmalh., which is native to the Middle East and adjacent
Europe. In contrast, yellow-flowered plants with sickle-shaped (rather than
coiled) pods are known as ssp. falcata
(L.) Arcang. (E. Small and Brooks, 1984; E. Small and Jomphe, 1989). These
diploid plants apparently are native to northern portions of Europe and Asia,
and have also been brought into cultivation. Molecular studies of the complex
based on chloroplast and mitochondrial markers have been confounded by the
unusual inheritance of the chloroplast genome, which is biparental with a
strong paternal bias (rather than the much more widespread maternal
inheritance), but Havananda et al. (2010) concluded that the blue- and
yellow-flowered diploid taxa are likely better treated as subspecies than as
species. Further complicating the issue of taxon recognition, the blue- and
yellow-flowered taxa are known to hybridize readily, producing an intergrading
swarm of offspring with mixtures of yellow, blue, violet, and variegated
corolla colors, and the hybrid germplasm is now widely distributed. The hybrids
have been called ssp. ×varia (Martyn)
Arcang. (Rabeler, 1984). However the hybrids form a continuum, with frequent
backcrossing, and are difficult to characterize morphologically (E. Small and
Brooks, 1984). The Missouri specimens have legumes coiled about 1.5 times,
which is consistent with some specimens of ssp. sativa, but have yellow corollas typical of ssp. falcata. Isely (1998) suggested that
true M. falcata is probably rather
rare in the U.S., and the Missouri plants probably fall somewhere within the
broad continuum of independent character-sorting in cultivated lineages with
contributions from both ssp. sativa
and ssp. falcata that sometimes have
been called ssp. ×varia. Because of
the ambiguous nature of the situation, no infraspecific taxa of M. sativa are recognized formally in the
current treatment.