Lactuca saligna

Morphological description

Biennial herbaceous plant generally 30 to 100 cm tall, with erect habit and stem simple or branched at the base. The stem is glabrous, whitish-bone colored, thinner compared to related species such as Lactuca serriola, lacking subspiny hairs. The root system, typical of biennial species, is well developed to support the vegetative and reproductive phases.

The basal leaves are pinnatifid-runcinate or sinuately toothed, glaucous green in color, with thin lobes and often elongated and acuminate apex. The cauline leaves are almost linear, entire or rarely slightly divided, with margin sometimes spiny on the lower vein, glaucous green in color, and clasp the stem through two acute and mucronate auricles, giving an appearance similar to willow leaves, from which the common name derives. The leaves often arrange themselves parallel to the sun’s rays, a behavior known as “compass grass.”

The inflorescence consists of numerous subsessile capitula, arranged in elongated and appressed spikes along the stem. Each capitulum has an involucre with lanceolate-obtuse scales arranged in 3-4 series. The flowers are all ligulate, hermaphroditic, pale yellow in color, often streaked with purple on the outer face, with actinomorphic symmetry and scapose habit (i.e., arranged terminally on long and thin peduncles).

The fruits are fusiform achenes (cypsela), light brown in color, with a subglabrous surface and a filiform beak about one and a half to twice the length of the achene body. The pappus is composed of simple white hairs, facilitating anemochorous dispersal (wind transport).

The internal latex is cream-colored, typical of the genus Lactuca.

Habitat and distribution

The species is widespread in central and southern Europe, in the Mediterranean basin, in North Africa, and in western Asia up to central Asia. In Italy it is present throughout the central and northern territory, including Corsica.

It grows mainly in mountainous and hilly environments, up to about 1000 meters altitude. It prefers uncultivated places, road edges, plowed fields, rubble, and rocky areas, with preferably calcareous substrate. It is a species that easily adapts to disturbed and poorly fertilized soils, typical of anthropized and semi-natural habitats.

Exposure is usually sunny, with preference for open and well-drained environments.

Flowering period

Flowering occurs mainly from May to August, with some variation linked to altitude and latitude. In some Mediterranean areas it can extend until September. The flowers appear in elongated spikes and are visible simultaneously along the stem.

Ecology and pollination

The plant is mainly pollinated by pollinating insects, attracted by the pale yellow color of the flowers and the presence of nectar. The morphology of the flowers, all ligulate and hermaphroditic, facilitates visits by bees, hymenopterans, and other pollinating insects.

Seed dispersal occurs through the feathery pappus which allows the fruit to be transported by wind, favoring effective colonization of new environments, especially in disturbed areas.

The plant is characterized by a particular phototropic behavior: the leaves tend to arrange themselves parallel to the sun’s rays, reducing evapotranspiration and optimizing photosynthesis.

Curiosities and traditional uses

The genus name Lactuca derives from the Latin "lac", meaning milk, referring to the white and creamy latex contained in the internal tissues of the plant, similar to that of other species in the genus.

The specific epithet "saligna" refers to the similarity of the leaves to those of the willow (Salix spp.), particularly evident in the narrow, linear cauline leaves with auricles clasping the stem.

Historically, as with other Lactuca species, the latex has been used in herbal medicine for its mildly sedative and analgesic properties, although Lactuca saligna is not among the species most exploited for medicinal or food purposes.

In local folklore, the leaves of Lactuca saligna, like those of Lactuca serriola, have been observed for their phototropic behavior, which gave rise to the nickname "compass grass," useful for orientation relative to the sun.

Etymology

The scientific name derives from the Latin "lac" (milk), referring to the white latex present in the plant, and from the adjective "salignus", meaning "similar to willow", for the shape of the cauline leaves.

The Italian common name “willow-leaved lettuce” directly recalls this leaf characteristic, which indeed resembles the narrow and elongated leaves of the willow.

Sources

• Prof. S. Pignatti, Flora d’Italia
• Acta Plantarum - Flora delle regioni italiane (sheet by Anja Michelucci)
• Tela Botanica / H. Coste, Flore descriptive et illustrée de la France
• World Flora Online (WFO)