Changes

:Chromosome number: ''x''= 8;''M. alba'': 2''n''= 16, 24, 32;''M. indica'': 2''n''= 16;''M. officinalis'': 2''n''= 16, 32;''M. suaveolens'': 2''n''= 16

* ''M. suaveolens'' : Daghestan sweetclover (En)*. Vietnam: nhãn hương.

Sweetclovers are widely distributed throughout Europe and Asia, mainly in temperate and subtropical areas, extending into North Africa, India ( ''M. indica'' ), Indo-China and Taiwan ( ''M. suaveolens'' ). ''M. alba'' and ''M. officinalis'' are cultivated extensively in North America, where they have attained their greatest importance in the Corn Belt and Great Plains of the United States and Canada, and in Eastern Europe and the Russian Federation. They have been introduced into Australia, South America and into eastern and southern Africa. ''M. indica'' is cultivated in India (mainly in the northern parts), in Pakistan and the United States. ''M. suaveolens'' is occasionally cultivated in China and North America.

*Annual or biennial, sometimes scented herbs. *Leaves trifoliolate; stipules adnate to the petiole, subulate; leaflets dentate. *Inflorescence an axillary raceme; flowers small; bracts small; bracteoles absent; calyx .*Calyx campanulate with 5 subequal teeth; corolla yellow or white, rarely purple, glabrous, caducous, standard usually longer than keel and wings, keel shorter than wings, obtuse, not adnate to stamens; stamens diadelphous, anthers uniform. *Fruit a small pod, straight, ovoid to nearly globose, with persistent pedicel and calyx, 1-4-seeded. *Seed smooth or nearly so.

* === ''M. alba'' . Erect, ascending or decumbent, sparsely branched, scented, annual herb, up to 1.5(-2.5) m tall, with long taproot. Stipules lanceolate to setaceous, 4-6 mm long; petiole 0.5-2 cm long, petiolule up to 5 mm; leaflets obovate to oblong-obovate, 1-2.5 cm × 5-12 mm, serrate-dentate almost to the base. Raceme 5-20 cm long, on an up to 4 cm long peduncle; flowers white, calyx about 2 mm long, corolla 4-6 mm long, style 1.7-2.3 mm long. Pod obovoid to ovoid, 4 mm long, reticulately veined, greyish to blackish-brown when ripe. Seed ovoid, about 2 mm long, yellow-brown.===

* ''M. indica'' . Erect, ascending or decumbent, sparsely branched, scented, annual herb , up to 60 cm tall1. Stem pubescent5(-2.5) m tall, with long taproot. *Stipules lanceolate to setaceous, 54-8 6 mm long; petiole up to 40.5 -2 cm long, petiolule up to 5 mm; leaflets oblong obovate to oblong-obovate, 0.81-2.5 cm × 25-9 12 mm, serrate-dentate almost to the base. *Raceme 105-16-flowered; peduncle 20 cm long, on an up to 3 4 cm long; flowers yellow; peduncle.*Flowers white, calyx about 1.5 2 mm long, teeth triangular-lanceolate; corolla 24-3 6 mm long; , style 01.97-12.2 3 mm long. *Pod 1-seededobovoid to ovoid, 1.5-4 mm long, prominently reticulately veined, olivegreyish to blackish-greenbrown when ripe. *Seed ovoid, about 2 mm long, yellow-brown, finely verrucose.

* === ''M. officinalisindica'' . An erect, much branched, scented annual or biennial with stout stem up to 1.5(-3) m tall and thickened roots. Stipules 3-6 mm long; petiole up to 3 cm long, petiolule up to 6 mm; leaflets obovate to oblong-lanceolate, 1-2.5 cm × 4-15 mm. Raceme up to 10 cm long, peduncle about 2 cm long; flowers 4.5-8(-10) mm long; calyx teeth equal, acute; corolla yellow; style 1.7-2.3 mm long. Pod ovoid, 3-6 mm long, glabrous, brown when ripe, transversely reticulate or irregularly rugose, usually 1-seeded. Seed ovoid, about 2 mm long, yellow-green.===

* Erect, annual herb up to 60 cm tall. Stem pubescent.*Stipules lanceolate to setaceous, 5-8 mm long; petiole up to 4.5 cm long, petiolule up to 5 mm; leaflets oblong to obovate, 0.8-2.5 cm × 2-9 mm.*Raceme 10-16-flowered; peduncle up to 3 cm long.*Flowers yellow; calyx about 1.5 mm long, teeth triangular-lanceolate; corolla 2-3 mm long; style 0.9-1.2 mm long.*Pod 1-seeded, 1.5-4 mm long, prominently reticulately veined, olive-green.*Seed ovoid, about 2 mm long, yellow-brown, finely verrucose. === ''M. suaveolensofficinalis'' === *An erect, much branched, scented annual or biennial with stout stem up to 1. 5(-3) m tall and thickened roots.*Stipules 3-6 mm long; petiole up to 3 cm long, petiolule up to 6 mm; leaflets obovate to oblong-lanceolate, 1-2.5 cm × 4-15 mm.*Raceme up to 10 cm long, peduncle about 2 cm long.*Flowers 4.5-8(-10) mm long; calyx teeth equal, acute; corolla yellow; style 1.7-2.3 mm long.*Pod ovoid, 3-6 mm long, glabrous, brown when ripe, transversely reticulate or irregularly rugose, usually 1-seeded.*Seed ovoid, about 2 mm long, yellow-green. === ''M. suaveolens'' === *Annual to biennial herb, up to 1.5 m tall, pubescent to subglabrous, with thickened roots. Stem erect, angular, glabrous. *Stipules 8-10 mm long; petiole up to 2 cm long, petiolule up to 1 mm; leaflets narrowly elliptical to obovate, 1-3 cm × 3-8 mm. *Raceme 10-15 cm long, densely flowered, elongate after anthesis; peduncle 2-5 cm long; flowers .*Flowers pale yellow, 3-4 mm long; style 1.7-2.3 mm long. *Pod ellipsoid, about 3 mm long, finely reticulate. *Seed ellipsoid, 2 mm long, reddish.

Well-ripened, mature seed is hard. Seed can be stored for long periods. After storage for 40 years in stoppered glass bottles, 60% of the seed still germinated in a trial in the United States. During the first year, biennial cultivars form a primary stem which becomes much branched under favourable conditions, a deeply penetrating taproot and, as the season progresses, a crown. When sweetclover is cut early, regrowth is from buds higher up the stem. Top growth reaches maximum development during late summer when a rapid increase in the size of the taproot begins which continues during autumn. Growth in the second year starts quickly and largely consists of rather coarse stems, which may reach to nearly 3 m in ''M. officinalis'' . Root thickening does not occur in annual cultivars. Control of flowering and taproot thickening is not fully understood. The flowering of biennial cultivars is initiated by long days. Under a daylength of 18 hours, flowering starts within 3 months after sowing. Vernalization seems to be of only minor importance.

Pollination is by insects, mostly honey bees. Flowers of ''M. alba'' and ''M. officinalis'' only set seed when tripped by visiting insects. ''M. alba'' and ''M. indica'' are self-fertile; self-incompatibility is common in ''M. officinalis'' .

''Melilotus'' comprises about 25 species found chiefly in the Mediterranean region and central Asia. The following characteristics may be useful to easily distinguish between the 4 species described here: ''M. indica'' : style length 0.9-1.2 mm (other species 1.7-2.3 mm); ''M. alba'' : flowers white (other species yellow); ''M. officinalis'' : pod strongly transversely veined (other species irregularly veined); ''M. suaveolens'' : style 1.7-2.3 mm long, flowers yellow, pod irregularly veined, plant very fragrant.

''M. alba'' and ''M. officinalis'' are closely related and sometimes hybridize naturally. Some authors prefer to write ''M. albus'' and ''M. indicus'' instead of ''M. alba'' and ''M. indica'' .

Sweetclover is affected by several diseases in the more humid parts of its area of cultivation in the United States and Canada. ''Phytophthora cactorum'' causes root rot and crown injury in the spring of the second year. ''Ascochyta caulicola'' and ''Cercospora davisii'' cause "black stem", characterized by stunted, blackened stems, poor flowering and reduced seed set. The sweetclover weevil ( ''Sitona cylindricollis'' ) is the main insect pest in North America. Seedlings are most vulnerable, adult plants may be defoliated, but generally survive and outgrow the damage.

A germplasm collection of some 1300 accessions is maintained at the Canada Department of Agriculture, Brandon, Canada. The development of strains with large seed, resistance to seedling diseases, winter hardiness, drought resistance, tolerance to acid and saline soils, and a higher proportion of permeable seed are objectives for improving these crops. Breeding work is being done in Canada, the United States and the Russian Federation. Cultivars with low coumarin content have been bred, following the discovery of a low-coumarin gene in ''M. dentata'' (Waldst. & Kit.) Pers. and its transfer into ''M. alba'' and ''M. officinalis'' .

*R.K. Arora & P.N. Mathur