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Published In: Species Plantarum 2: 778–779. 1753. (1 May 1753) (Sp. Pl.) Name publication detailView in BotanicusView in Biodiversity Heritage Library

Project Name Data (Last Modified On 8/29/2017)
Acceptance : Accepted
Project Data     (Last Modified On 7/9/2009)
Status: Introduced


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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.



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