Amaranthus retroflexus

Morphological description

Annual herbaceous plant, monoecious, with an erect habit and height varying between 20 and 100 cm, but sometimes reaching up to 300 cm. The stem is robust, erect and from simple to branched, with a woody texture in the lower part; it has a light green color tending to reddish especially at the base, while the surface is striated and pubescent in the upper part and on the branches, which bear a dense inflorescence.

The leaves are long-petiolate, with the petiole that can also reach the length of the blade. The leaf blade is ovate-rhomboid or elliptical in shape, with dimensions ranging from 2 to 15 cm in length by 1-7 cm in width. The apex can be acute, obtuse or flat, and the margin shows a slight undulation. The lower surface of the leaf shows well-marked and pubescent veins.

The inflorescence is a compact panicle consisting of terminal and lateral spikes of similar size, with the apex often reflexed (bent backward), from which the epithet "retroflexus" derives. The flowers are unisexual and pentamerous, with spatulate-ovate or lanceolate-spatulate tepals, white or whitish in color, about 2.5-4 mm long. The bracts of the female flowers are lanceolate or subulate, with a rigid and sharp terminal mucro, longer than the tepals (3.5-6 mm). Each male flower has five stamens longer than the perianth, while the stigmas of the female flowers are 2 or 3.

The fruit is a subglobose (pissidium) ellipsoid capsule, similar in size to the perianth, which opens horizontally (dehiscent). The seeds are lenticular in shape, dark brown or reddish in color, with a wrinkled and shiny surface, about 1-1.4 mm in diameter.

The root system is not specifically described in the consulted sources, but as an annual herbaceous species it is presumed to have a taproot or fasciculate root system typical of plants colonizing disturbed habitats.

Habitat and distribution

Native to North America, it is now a cosmopolitan species widespread in all temperate zones of the world. In Italy and the Mediterranean basin it commonly grows in anthropic and disturbed habitats such as cultivated fields, uncultivated land, ruins, rubble, gravel areas and along riverbeds, from sea level up to about 900 m altitude.

It prefers well-drained soils, often gravelly or sandy, and conditions of sunny or partially shaded exposure. It is frequently considered a weed due to its adaptability and rapid growth in open and disturbed environments.

Flowering period

Flowering extends from May to October, with possible variation depending on altitude and latitude. In Italy, the plant generally flowers from late spring to late autumn, taking advantage of the warm seasons for seed production.

Ecology and pollination

The species has unisexual flowers with male and female flowers mixed in the inflorescence, favoring cross-pollination. The morphology of the flowers, small and inconspicuous with white tepals, suggests an adaptation to anemophilous pollination (pollen transport by wind), although occasional insect visits are not excluded.

Seed dispersal occurs through horizontal dehiscence of the fruit, which releases small, shiny and wrinkled seeds, easily transported by wind, water or human activities. Rapid germination and growth allow this species to quickly colonize open and disturbed spaces.

Curiosities and traditional uses

Common amaranth is an edible species with various food and traditional uses. The leaves, harvested in rosette stage, are consumed as a vegetable, usually boiled for soups, with a taste reminiscent of spinach. The young stem, before the development of the inflorescence, can be used like asparagus.

The seeds, ground and used as flour, enrich the diet with proteins, representing an alternative resource to traditional cereals. From a nutritional point of view, the plant is rich in vitamins A and C, calcium and iron, with astringent and revitalizing properties, traditionally used to improve the health status of debilitated individuals.

However, it is important to avoid using the cooking water of the leaves, because the plant accumulates nitrates that can contaminate the water.

Etymology

The genus name, Amaranthus, derives from the Greek "a-maraino" meaning "I do not wither", referring to the calyx and the scarious bracts of the plant that seem never to wither. In the past it was also interpreted as "imperishable" or, by other authors, as deriving from "amor" and "anthos" (flower of love).

The specific epithet retroflexus refers to the characteristic central spike of the inflorescence that often folds backward. The common Italian name "amaranto comune" emphasizes its wide distribution and recognizability among amaranth species.

Sources

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