Flora of North America species comparison

Medicago lupulina is valued as a pasture plant (there are several cultivars), cover crop, and as a green manure plant; it is typically plowed under in the fall as part of a crop rotation. Although M. lupulina is often considered a lawn weed, nitrogen fixation associated with this plant contributes to lawn health.

Medicago lupulina is a variable species, but the variation is not structured in ways that can reasonably be classified formally. Of the many criteria that have been used to delimit infraspecific groups, presence of gland-tipped hairs and whether annual/biennial or perennial have been most frequently employed. Density of glandular trichomes is highly variable in the species (L. R. Goertzen and E. Small 1993), and taxa such as M. lupulina var. glandulosa Neilreich have no merit.

(Discussion copyrighted by Flora of North America; reprinted with permission.)

Species ca. 85 (13 in the flora).

Several species of Medicago not treated here have been recorded very rarely in the flora area, particularly as coastal, ballast waifs. These include Medicago disciformis de Candolle, collected in 1949 from Worcester County, Massachusetts (Johnson s.n., DINH, now transferred to CONN); M. monantha (C. A. Meyer) Trautvetter collected in 1884 from Middlesex County, Massachusetts (Swan s.n., NEBC); and M. sphaerocarpa Bertoloni, collected in 2016 from Santa Catalina Island, California, by C. M. Guilliams (SBBG). Several annual species are present in parts of the flora area because they escape from experimental or commercial forage cultivation; additional introduced species will likely be discovered, and because the majority are of Mediterranean origin, it will likely be in California and the southern states. All of the species treated here have shown weedy tendencies in some areas outside of the flora area, while some are weeds in the flora area. None is significantly troublesome.

Medicago sativa is arguably the most important temperate region forage plant in the world. Several other perennial species, and, more commonly, annual species, which are commonly called medics or medicks, are cultivated for forage, but infrequently in the flora area.

Species in sect. Spirocarpos, all with coiled fruits, normally have two rows of prickles on the dorsal suture, but in some plants these are reduced to tubercles or the dorsal sutures are without ornamentation. Cultivars often have been selected for lack of fruit prickles, as this prevents entanglement in fur and makes the nutritious fruits easier for livestock consumption. Cultivars have been grown in the flora area, increasing the likelihood that prickleless-fruited forms will be encountered. The prickles protect the fruit, serve to adhere to fur for distribution, and perhaps also to facilitate burial of the indehiscent fruits in soil. In their native area, prickly and prickleless forms occur randomly on a geographic basis. The literature is replete with extensive infraspecific classifications of the species on the basis of presence and length of prickles.

In the nineteenth and twentieth centuries, Medicago was controversially separated from Trigonella, less controversially from Melilotus, with given species assigned to these and many other genera depending on taxonomic treatment. Recent morphological, chemical, and molecular evidence has made it clear that Medicago is well demarcated from its nearest allies, including Trigonella, Melilotus, and Trifolium. Medicago flowers have an irreversible explosively tripping pollination mechanism, which is degenerate in the annual species, but evident by a syndrome of floral characteristics. Although fruits of Medicago are usually indispensable for species identification, flowers suffice for distinguishing Medicago from allied genera. Contrasting characters possessed by Medicago but not related genera include: banner, except when very small, with major basal vein usually with more than three branches near base; horn of wing petal large, about one-third of wing limb; keel very strongly adherent to wing by a wing spur in a keel invagination; androecium with apex of fused portion of anther column arched, alternating distinct portions of filaments often relatively thick; stigma fungiliform; style always short.

Several character states are unique to one or just a few species in the flora range. Medicago arabica is the only species in which the fruit has a dorsal suture with a pattern of four ridges separated by three grooves. Medicago lupulina is the only species that has one-seeded fruits. Medicago monspeliaca is the only species that has deflexed fruit and a stellate inflorescence; M. monspeliaca and M. orbicularis are the only species with rough-surfaced seeds. Medicago orbicularis is the only species with papery pod edges (although M. scutellata fruits are somewhat reminiscent). Medicago sativa is the only species that has violet or purple flowers. Medicago scutellata is the only species that has fruit resembling a stack of bowls. Medicago rigidula, M. truncatula, M. turbinata, and sometimes M. polymorpha have fruits that are extremely hard-walled at maturity, while the remaining species have fruit walls that are flexible or relatively easily bent.

Several forage species have a number of widely used common names, some often more or less confined to Europe, Australia, or different areas of the United States. Only vernacular names that have been used repeatedly in the literature are reported here.

Perennial species of Medicago are slightly to substantially outbreeding, while annual species are mostly strongly inbreeding.

(Discussion copyrighted by Flora of North America; reprinted with permission.)