Centaurea cyanus

Morphological description

Annual herbaceous plant, Centaurea cyanus reaches a height between 30 and 100 cm. The stem is erect, simple or branched especially towards the apex, rigid, striated and covered by a fine whitish cobwebby-tomentose hairiness. The plant has a taproot system that is slender.

The basal leaves are petiolate, lyrate in shape with a lanceolate outline and provided with 2-4 lobes; the terminal lobe is larger than the others. They generally measure from 3 to 7 cm in length and from 0.3 to 0.8 cm in width. The upper surface is covered by fine down, while the lower surface is cottony. The cauline leaves are sessile, linear-lanceolate, narrow, small in size (2-3 cm), with entire margins and attenuated base, and are not decurrent along the stem.

The inflorescence consists of solitary heads or grouped in rare corymbs, each 2-3 cm in diameter, supported by erect and elongated leafless branches. The involucre is campanulate-pyriform, 9-16.5 mm long and 4-9 mm wide, formed by dark green outer bracts with tomentose surface and brown-dark, scarious and fringed appendages with thin cilia about 0.3 mm long, and longer inner bracts with a denticulate apex about 1 mm. The bracts are spineless.

The flowers are all tubular and blue-violet in color (sometimes they can vary towards white or purple). The corollas are divided into five lobes; the outer ones, sterile, are radiate and larger (20-25 mm), while the inner flowers, hermaphroditic, are smaller (10-15 mm). The ovary is inferior. The fruit is an obovate achene, 3-5 mm long, gray-brown in color, covered by scattered fine hairs. It is equipped with a reddish pappus formed by biseriate bristles, the outer ones as long as the achene, the inner ones shorter (1-2 mm).

Habitat and distribution

Centaurea cyanus is widespread in Italy and much of the Mediterranean area, with a range that extends mainly in coastal and mountainous areas up to about 1500 meters altitude. It is typical of agricultural soils, particularly cereal fields, and is commonly found in hoed soils, meadows and uncultivated places with nitrogen presence in the soil. It prefers sunny exposures, with well-drained and medium-textured soils.

In Italy the species is still quite widespread, but its presence is declining due to the intensive use of selected seeds and herbicides in cereal crops. However, it is preserved in some protected areas, such as the Monti Sibillini Park, where it can form extensive carpets of blue flowers in plains and field margins.

Flowering period

The flowering of Centaurea cyanus extends from April to August, with a peak that slightly varies depending on altitude and latitude. In mountainous areas, flowering can shift towards the summer months, while in lower and temperate zones it starts early in spring.

Ecology and pollination

The plant is pollinated by pollinating insects, mainly bees and butterflies, attracted by the bright color and nectar of the tubular flowers. The blue-violet corolla, with sterile but showy outer flowers, has an attractive function for pollinators. Centaurea cyanus presents a reproductive strategy that combines sterile radiate flowers and fertile inner flowers, thus maximizing visibility and pollination efficiency.

Seed dispersal occurs through achenes equipped with a bristly pappus, which facilitates wind transport over short distances. Moreover, presence in agricultural habitats favors accidental dispersal through machinery and human activities.

Curiosities and traditional uses

Centaurea cyanus is a medicinal species with numerous traditional uses. In folk medicine it is used in decoctions for the treatment of conjunctivitis, edema, gout, rheumatism and stye, as well as a cough remedy. It contains glycosides, including “cyanine”, an anthocyanic glycoside also used as a natural dye, sesquiterpenic flavonoids, tannins, potassium salts and mucilages.

In homeopathy, it is used to treat flu attacks, menstrual cycle disorders, constipation problems and liver disorders. In cooking, the leaves are a source of a natural dye mainly used to decorate sweets.

Curiously, despite being a dye, cyanine is not used for coloring fabrics because it degrades easily in light and in the presence of acids. In floriculture, several ornamental varieties have been selected with larger flowers and variable shades, from dark blue to pink and purple.

Etymology

The genus name derives from the Greek κέντρον (kéntron), meaning "goad" or "spur", probably referring to the pointed shape of the bud, or from the myth of the centaur Chiron, master of medicine and sciences, from Latin centaureum. The specific epithet cyanus derives from the Greek κύανος (kýanos), meaning "blue", referring to the typical color of the corollas.

The common Italian name "fiordaliso" refers to the delicate shape and bright color of the flower, often associated with the simple beauty of cultivated fields.

Sources

• Acta Plantarum - Flora delle regioni italiane (actaplantarum.org)
• Acta Plantarum - Scheda di Nino Messina
• World Flora Online (WFO)