Medicago is a genus of flowering plants, commonly known as medick or burclover, in the legume family (Fabaceae). It contains at least 87 species. The genus name is based on the Latin name for that plant, medica, from Greek: μηδική (πόα)Median (grass).
The genus is distributed mainly around the Mediterranean Basin, also extending across temperate Eurasia and sub-Saharan Africa. Its best-known member is alfalfa (M.sativa), an important forage crop.
Description
Most members of the genus are low, creeping herbs, resembling clover, but with burs (hence the common name). However, alfalfa grows to a height of 1 metre (3+1⁄2ft), and tree medick (M.arborea) is a shrub. Members of the genus are known to produce bioactive compounds such as medicarpin (a flavonoid) and medicagenic acid (a triterpenoid saponin). Chromosome numbers in Medicago range from 2n = 14 to 48.
The species Medicago truncatula is a model legume due to its relatively small stature, small genome (450–500 Mbp), short generation time (about 3 months), and ability to reproduce both by outcrossing and selfing.
Comprehensive descriptions of the genus are Lesinš and Lesinš 1979 and Small and Jomphe 1989. Major collections are SARDI (Australia), USDA-GRIN (United States), ICARDA (Syria), and INRA (France).
Species
The genus contains at least 87 species.
Recent molecular phylogenic analyses of Medicago indicate that the sections and subsections defined by Small & Jomphe, as outlined below, are generally polyphyletic. However, with minor revisions sections and subsections could be rendered monophyletic.
The status of the following species is unresolved:
Medicago agropyretorum Vassilcz.
Medicago alatavica Vassilcz.
Medicago caucasica Vassilcz.
Medicago cyrenaea Maire & Weiller
Medicago difalcata Sinskaya
Medicago grossheimii Vassilcz.
Medicago gunibica Vassilcz.
Medicago hemicoerulea Sinskaya
Medicago karatschaica (A. Heller) A. Heller
Medicago komarovii Vassilcz.
Medicago meyeri Gruner
Medicago polychroa Grossh.
Medicago schischkinii Sumnev.
Medicago talyschensis Latsch.
Medicago transoxana Vassilcz.
Medicago tunetana (Murb.) A.W. Hill
Medicago vardanis Vassilcz.
Medicago virescens Grossh.
Evolution
Medicago diverged from Glycine (soybean) about 53–55 million years ago (in the early Eocene), from Lotus (deervetch) 49–51 million years ago (also in the Eocene), and from Trigonella 10–22 million years ago (in the Miocene).
Etymology
The genus name is based on the Latin name for alfalfa, medica, from Greek: μηδική (πόα)Median (grass).
Béna et al. (2005) constructed a molecular phylogeny of 23 Sinorhizobium strains and tested the symbiotic ability of six strains with 35 Medicago species. Comparison of these phylogenies indicates many transitions in the compatibility of the association over evolutionary time. Furthermore, they propose that the geographical distribution of strains limits the distribution of particular Medicago species.
Agronomic research has been conducted on Medicago species. Other than its best-known member, alfalfa, several of the prostrate members of the family (such as M.lupulina and M.truncatula) have been used as forage crops. Select species in the Medicago genus naturally develop spiney pods during the reproductive phase of growth (such as M.intertexta and M.polymorpha). Despite having high levels of agronomic performance, these are typically viewed as undesirable in sheep based farming systems due to their ability to become lodged in wool, reducing fleece value. Breeding efforts in the 1990s have yielded spineless varieties of burr medic, providing valuable production amongst farming systems in low rainfall (<300mm annual), free draining, alkaline soils.
Notes
↑ Some sources treat Medicago citrina as a synonym of Medicago arborea.
↑ The validity of Medicago sinskiae has been questioned by Small and Jomphe, 1988.
↑Lesinš KA, Lesinš I (1979). Genus Medicago (Leguminosae): A Taxogenetic Study. The Hague, The Netherlands: Dr. W. Junk B. V. Publishers. p.132. ISBN978-90-6193-598-8.
Downie SR, Katz-Downie DS, Rogers EJ, Zujewski HL, Small E (1998). "Multiple independent losses of the plastid rpoC1 intron in Medicago (Fabaceae) as inferred from phylogenetic analyses of nuclear ribosomal DNA internal transcribed spacer sequences". Can J Bot. 76 (5): 791–803. Bibcode:1998CaJB...76..791D. doi:10.1139/b98-047.
