Lably
Skip to content

Allium

Genus of flowering plants

  • 12 min read
  • 9 chapters
Flowering ramsons (in Groß-Gerau , Hesse , Germany )
Thomas Pusch · CC BY-SA 4.0

Related on Lably

Through Monocotyledon, Temperate climate and Flower

Lab · Class 11Anatomy of Flowering Plants — Animated Chapter FilmLab · Class 11Plant Tissue AnatomyLab · Class 9–11Inside a PlantLab · Class 8–12Using a Microscope

Allium species occur in temperate climates of the Northern Hemisphere, except for a few species occurring in Chile (such as A. juncifolium), Brazil (A. sellovianum), and tropical Africa (A. spathaceum). They vary in height between 5–150 centimetres (2–59 in). The flowers form an umbel at the top of a leafless stalk. The bulbs vary in size between species, from small (around 2–3 mm in diameter) to rather large (8–10 cm). Some species (such as Welsh onion A. fistulosum and leeks (A. ampeloprasum)) develop thickened leaf-bases rather than forming bulbs as such.

Carl Linnaeus first described the genus Allium in 1753. The generic name Allium is the Latin word for garlic, and the type species for the genus is Allium sativum which means "cultivated garlic". The decision to include a species in the genus Allium is taxonomically difficult, and species boundaries are unclear. Estimates of the number of species are as low as 260, and as high as 979. In the APG III classification system, Allium is placed in the family Amaryllidaceae, subfamily Allioideae (formerly the family Alliaceae). In some of the older classification systems, Allium was placed in Liliaceae. Molecular phylogenetic studies have shown this circumscription of Liliaceae is not monophyletic.

Various Allium species have been cultivated from the earliest times. About a dozen species are economically important as crops, or garden vegetables, and an increasing number of species are important as ornamental plants. Plants belonging to this genus produce cysteine-derived organosulfur compounds, which impart a distinctive onion or garlic flavor and scent. Many are used as food plants, though not all members of the genus are equally flavorful. In most cases, both bulb and leaves are edible. The characteristic Allium flavor depends on the sulfate content of the soil the plant grows in. In the rare occurrence of sulfur-depleted growth conditions, all Allium species completely lose their usual odors and flavors.

Description

The genus Allium (alliums) is characterised by herbaceous geophyte perennials with true bulbs, some of which are borne on rhizomes, and an onion or garlic odor and flavor.

The bulbs are solitary or clustered and tunicate and the plants are perennialized by the bulbs reforming annually from the base of the old bulbs, or are produced on the ends of rhizomes or, in a few species, at the ends of stolons. A small number of species have tuberous roots. The bulbs' outer coats are commonly brown or grey, with a smooth texture, and are fibrous, or with cellular reticulation. The inner coats of the bulbs are membranous.

Many alliums have basal leaves that commonly wither away from the tips downward before or while the plants flower, but some species have persistent foliage. Plants produce from one to 12 leaves, most species having linear, channeled or flat leaf blades. The leaf blades are straight or variously coiled, but some species have broad leaves, including A. victorialis and A. tricoccum. The leaves are sessile, and very rarely narrowed into a petiole.

The flowers, which are produced on scapes are erect or in some species pendent, having six petal-like tepals produced in two whorls. The flowers have one style and six epipetalous stamens; the anthers and pollen can vary in color depending on the species. The ovaries are superior, and three-lobed with three locules.

The fruits are capsules that open longitudinally along the capsule wall between the partitions of the locule. The seeds are black, and have a rounded shape.

The terete or flattened flowering scapes are normally persistent. The inflorescences are umbels, in which the outside flowers bloom first and flowering progresses to the inside. Some species produce bulbils within the umbels, and in some species, such as Allium paradoxum, the bulbils replace some or all the flowers. The umbels are subtended by noticeable spathe bracts, which are commonly fused and normally have around three veins.

Some bulbous alliums increase by forming little bulbs or "offsets" around the old one, as well as by seed. Several species can form many bulbils in the flowerhead; in the so-called "tree onion" or Egyptian onion (A. × proliferum) the bulbils are few, but large enough to be pickled.

Many of the species of Allium have been used as food items throughout their ranges. There are several unrelated species that are somewhat similar in appearance to alliums but are poisonous (e.g. in North America, death camas, Toxicoscordion venenosum), but none of these has the distinctive scent of onions or garlic.

Sign in to keep reading

8 more chapters are free with a Lably account.

More in Plants

Molecular phylogeneticsBranch of phylogeny that analyzes genetic, hereditary molecular differencesMicrometreUnit of length; one millionth of a metrePerennialPlant that lives for more than two yearsDeciduousPlants that shed leaves seasonallyGram-negative bacteriaGroup of bacteria that do not retain the Gram stain used in bacterial differentiationLegumePlants in the family Fabaceae