Annual

annual, plant that germinates from seed, blossoms, produces seed, and dies within one year. Annuals propagate themselves by seed only, unlike many biennials and perennials. They are thus especially suited to environments that have a short growing season. Cultivated annuals are usually considered to be of three general types: tender, half-hardy, and hardy. Tender and half-hardy annuals do not mature and blossom in one ordinary temperate growing season unless they are started early under glass and are set outdoors as young plants. Hardy annuals are usually sown where they are expected to bloom. Quite often they reseed themselves year after year. Blooming is prolonged by cutting the flowers before the seeds can form. Typical annual flowers are cosmos, larkspur, petunia, and zinnia; annual vegetables include corn, tomatoes, and wheat.

Bibliography

See H. G. W. Fogg, Dictionary of Annual Plants (new ed. 1972).

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annual

Any plant that completes its life cycle in a single growing season. The dormant seed is the only part of an annual that survives from one growing season to the next. Annuals include many weeds, wildflowers, garden flowers, and vegetables. See also biennial, perennial.

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annual

a plant that completes its life cycle in less than one year

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Annual 

a plant that completes its life cycle within a single growing season of usually two to five months. The seeds usually sprout in the spring or summer; by autumn (in temperate climates) the plant is bearing fruit and dying. Annuals include flax, millet, buckwheat, spring wheat, corn cockle, and wild oats. Annual plants that develop particularly rapidly are known as ephemerals; they often mature in four to ten weeks. Some annuals, including knapweeds and shepherd’s purse, can survive the winter in the rosette phase if germination occurs late in the season.

Annuals grow only in those regions where they can complete their growth cycle in the period of a single year. Their numbers are greatest in desert areas and fewest in tundras. Annuals are most common where the plant cover is the least dense. In areas where dense plant cover is present, as in meadows, the annuals generally obtain supplementary nourishment through parasitism or symbiosis; these annuals include such hemiparasites as Alectrolophus, eyebright, and cowwheat, as well as such mycotrophic plants as clover, alfalfa, and gentian. As growing conditions worsen (with increasingly higher latitudes in the northern hemisphere or higher elevations in the mountains), the number of annual plants declines. Some species that are not able to complete their life cycle in harsh conditions in one year become perennials; an example is annual blue grass, which becomes a perennial in arctic and alpine settings.