Trigonella officinalis

Morphological description

Biennial herbaceous plant belonging to the Fabaceae family, Melilotus officinalis presents a habit that can vary from prostrate-ascending to erect and branched, reaching a height between 50 and 150 cm. The stems are numerous, branched, grooved, and often hollow, giving the plant a robust yet flexible structure.

The root system is characterized by a taproot, deep and sometimes tuberous, allowing good anchorage and effective absorption of water and nutrients even in poor or rocky soils.

The leaves are alternate, petiolate, and trifoliate, with elliptic-elongated leaflets that can reach 10-25 mm in the upper leaves. The margins of the leaflets are irregularly serrated, while the central leaflet is longer and equipped with an elongated rachis. The stipules are strap-shaped and entire, contributing to easy identification of the species.

The inflorescence is a pedunculate raceme 4 to 10 cm long, positioned above the axillary leaf. It contains 30 to 70 small pendulous flowers, bright yellow in color and endowed with a pleasant fragrance that attracts numerous pollinating insects. The flowers are papilionaceous, with a zygomorphic corolla 4.5 to 7 mm long; the standard is similar in size to the wings, which in turn are longer than the keel. The calyx is bell-shaped with five linear and subequal teeth, shorter than half of the corolla.

The fruit is a small indehiscent legume called camara, oval and pendulous, 2.5 to 3.5 mm long, glabrous and light brown at maturity. It has a transversely reticulate and sinuous venation, containing one or two ovoid and smooth seeds.

Habitat and distribution

Melilotus officinalis is widely distributed in Italy and the Mediterranean basin. It prefers open environments such as rubble, uncultivated fields, roadsides, and disturbed areas, showing excellent adaptability to poor and often calcareous soils. The species generally grows from 0 up to about 1500 meters in altitude, finding favorable conditions in mountainous and hilly areas.

In Italy it is present throughout most of the territory, while in the Mediterranean its distribution is subcosmopolitan, being present in almost all temperate regions of the world, although with some geographical gaps.

Flowering period

Flowering mainly occurs between May and August, with possible local variations related to altitude and climatic conditions. In warmer climates, flowering can start as early as May, while at higher altitudes it tends to concentrate in the summer months.

Ecology and pollination

The yellow and fragrant flowers of Melilotus officinalis are very attractive to pollinating insects, particularly bees and other hymenopterans, which play a crucial role in the species’ pollination. The plant produces a significant amount of nectar and pollen, making it a valuable resource for pollinators and thus contributing to the biodiversity of the ecosystems where it is found.

Seed dispersal mainly occurs by natural fall, thanks to the pendulous structure of the fruit which facilitates deposition near the mother plant, but it can also be aided by animals or humans, especially in cultivated or disturbed areas.

Curiosities and traditional uses

Melilotus officinalis contains coumarinic derivatives, aromatic substances that develop especially during drying and give the plant a characteristic hay-like scent. These compounds are responsible for the sedative and antispasmodic properties recognized in the plant, which has traditionally been used to promote sleep, soothe nervous irritations, neuralgia, headaches, and digestive disorders.

In folk medicine, Melilotus has also been used as a diuretic and as a balsamic expectorant. For external use, infusions of the plant have been used in decongestant washes for eyelids, mouth, throat, and minor wounds, thanks to its astringent and mild sedative properties.

It should be noted, however, that coumarin, while beneficial in moderate amounts, can be slightly toxic if taken in excess; therefore, therapeutic uses must be carried out with caution.

Besides medicinal uses, young leaves of Melilotus are consumed in salads, while the plant is also appreciated in beekeeping as a melliferous plant, contributing to honey production. In agriculture, it is used as forage and for soil improvement, thanks to its ability to fix nitrogen.

Etymology

The genus name "Trigonella" derives from the Greek τρίγωνος (trígonos) meaning "triangular," referring to the shape of the leaves composed of three leaflets. The specific epithet "officinalis" indicates the medicinal use of the plant, traditionally employed in herbal medicine and pharmacopoeia.

The common Italian name "Meliloto" recalls the characteristic sweet aroma of the plant, derived from coumarinic compounds that resemble the smell of honey ("meli-") and sweetness ("-loto"), also highlighting its value as a melliferous plant.

Sources

• Acta Plantarum - Flora delle regioni italiane (scheda di Anja Michelucci)