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plant that germinates from seed, blossoms, produces seed, and dies within one year. Annuals propagate themselves by seed only, unlike many biennialsbiennial,
plant requiring two years to complete its life cycle, as distinguished from an annual or a perennial. In the first year a biennial usually produces a rosette of leaves (e.g., the cabbage) and a fleshy root, which acts as a food reserve over the winter.
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 and perennialsperennial,
any plant that under natural conditions lives for several to many growing seasons, as contrasted to an annual or a biennial. Botanically, the term perennial applies to both woody and herbaceous plants (see stem) and thus includes numerous members of the kingdom.
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. 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.


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



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.


a plant that completes its life cycle in less than one year
References in periodicals archive ?
Suicide rates peak in the spring in the northern hemisphere (Goodwin, 1986), which is the time of the nadir of circannual testosterone levels in the human male (Dabbs, 1990).
One well-accepted hypothesis is that patterns of melatonin mediate the synchronization between an endogenous circannual rhythm in reproductive activity and the external annual rhythm in day length.
Circannual rhythms and interactions of vitamin D metabolites, parathyroid hormone, and biochemical markers of skeletal homeostasis: a prospective study.
We monitored circannual and circadian patterns of wallowing frequency by American bison during 1996-1997 in the tallgrass prairie region of eastern Kansas.
Circannual cycle in plasma testosterone levels in man.
gametogenesis, gamete release, larval release) in marine species is commonly entrained by environmental factors with circannual, lunar, or semilunar rhythms, or is triggered by specific temperatures or photoperiods (reviewed by Korringa 1947, Giese and Kanatani 1987, Neumann 1987, Santelices 1990, Brawley and Johnson 1992).
Circaseptan (about weekly) and circannual (about yearly) rhythms are examples of infradian rhythms.
Circannual rhythm A rhythm with a period of approximately 1 year.
Photoperiod: main proximal and distal factor of the circannual cycle of reproduction in farm animals.
Circannual variation of total testosterone has been studied in women in three studies, one of which demonstrated a statistically significant seasonal variation (24).
The parr-smolt transformation is subject to an endogenous circannual rhythm in which hypoosmoregulatory ability peaks during a period of a few weeks (Lundqvist and Eriksson 1985), and fish must achieve a minimum size for migration prior to this narrow time window (Elson 1957, Bilton et al.
Such continuous rectilinear photoperiods have previously been used to detect circannual rhythms (Randall et al.