Trigonella L.

The generic boundaries of Trigonella underwent dramatic changes in the past decades. Based on flower tripping mechanism numerous ‘medicagoid’ members were transferred to the genus Medicago (see Small 1987, Small & al. 1987, Small & Jomphe 1989) and molecular data approved this transfer (e.g. Bena 2001). The remainder of the genus Trigonella, however, still is a polyphyletic assemblage with about 55 species. The same molecular studies have shown that all species releasing coumarin (including fenugreek) are in fact nearer to Melilotus than to the other species of Trigonella. For reasons of priority the latter would then best include all species traditionally accommodated in Melilotus. The non-coumarin species of Trigonella should be divided over several smaller genera, some not yet described. Pending further studies Trigonella and Melilotus are here kept as separate genera with only the ‘medicagoid’ species of the former being removed from it. Since Medicago and Trigonella are very closely related and morphologically hardly separated, one should consult the accounts for both genera. See under Medicago for the distinction of Medicago and Trigonella.   
Trigonella is mainly distributed in the Mediterranean area and Macaronesia with some species also occurring in South Africa and Australia (Mabberley 2008). One species, Trigonella foenum-graecum, is economically important (fenugreek): it is cultivated for fodder (including birdseed) or as a spice plant in large parts of the world (but probably less so today). A second species, Trigonella caerulea, was also formerly cultivated for fodder and used to be a regular alien in Belgium but it is only exceptionally seen these days. Several other species are weeds of agricultural land and are sometimes introduced outside their natural distribution range.
The presence of (mature) pods is essential for the identification of species of the genus Trigonella.

1 Flowers solitary or paired. Corolla cream, sometimes tinged with violet. Calyx tubular, 6-8 mm long. Pod linear, 60-110 mm long === Trigonella foenum-graecum
Flowers more numerous. Corolla pure yellow, blue or whitish. Calyx campanulate, 2-4 mm long. Pod variable in outline, at most 50 mm long (often much shorter) === 2

2 Pod much flattened, 5-8 mm wide, membranous, with ciliate-spiny margins. Corolla whitish === T. arabica
Pod linear, not distinctly flattened and membranous. Corolla pure yellow or blue === 3

3 Corolla blue, sometimes very pale. Pod up to 5 mm long === 4
Corolla pure yellow. Pod at least 10 mm long === 5

4 Inflorescence capitate, not elongating in fruit (about as long as wide at maturity). Stem usually erect === T. caerulea
Inflorescence much elongating in fruit, many times longer than wide at maturity. Stem often procumbent, less frequently erect === T. procumbens

5 Pod 30-45(-50) mm long, erect to patent at maturity, not deflexed. Corolla 8-10(-12) mm long === T. caelesyriaca
Pod 10-15(-20) mm long, deflexed at maturity. Corolla 6-7 mm long === 6

6 Calyx teeth unequal. Fruiting peduncle up to 60 mm long. Inflorescence with 8-20 flowers === T. esculenta
Calyx teeth equal. Fruiting peduncle up to 20 mm long. Inflorescence with 3-10 flowers === T. maritima

Additional aliens: Trigonella calliceras Fisch. (W-As., wool alien), T. hierosolymetana Boiss. (syn.: T. hamosa L. nomen rej., T. spruneriana Boiss. subsp. hierosolymetana (Boiss.) Ponert) (E-Medit., W-Asia, grain alien), T. spinosa L. (E-Medit., wool alien) and T. stellata Forssk. (SW-As., N-Afr., Macaronesia, wool alien).


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Taxonomic name: 
Scratchpads developed and conceived by (alphabetical): Ed Baker, Katherine Bouton Alice Heaton Dimitris Koureas, Laurence Livermore, Dave Roberts, Simon Rycroft, Ben Scott, Vince Smith