hornwort

hornwort
/hawrn"werrt', -wawrt'/, n.
any aquatic plant of the genus Ceratophyllum, found in ponds and slow streams.
[1795-1805; HORN + WORT2]

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Any member of four to six genera of creeping annual or perennial plants of the class Anthocerotopsida.

Hornworts usually grow on damp soils or on rocks in tropical and warm temperate regions. The gametophyte typically is a flattened structure covered with small irregular lobes; the sporophyte forms a tapered cylinder (see alternation of generations). Rhizoids (rootlike structures) on the undersurface anchor the plant. Cavities in the gametophyte sometimes contain colonies of the cyanobacterium Nostoc (see cyanobacteria, nostoc). Hornworts have a region of continuous growth at the base of the sporophyte, and a large, irregular foot. The stalk that attaches the foot to the spore-bearing capsule in liverworts is absent in hornworts.

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also called  horned liverwort 

      any member of 6–7 genera, containing about 300 species of creeping annual or perennial plants of the class Anthocerotopsida. In some classification systems, hornworts have been grouped as horned liverworts in the subclass Anthocerotidae (class Hepaticae), class Anthocerotopsida, order Anthocerotales, or entirely separated from the bryophytes in the division Anthocerotophyta. Most evidence from morphological and developmental studies suggest that the hornworts are only distantly related to mosses and liverworts, but molecular evidence has not confirmed this view. Thus, the classification of hornworts remains controversial.

      The largest genus, Anthoceros, has a worldwide distribution. Dendroceros and Megaceros are mainly tropical genera. Hornworts usually grow on damp soils or on rocks in tropical and warm temperate regions. The plants' gametophytes (gametophyte) (sexual generation) are typically flattened, irregularly lobulated (thallose) structures that are usually less than 2 cm (0.8–1.6 inches) in diameter. The sporophyte, or asexual generation, forms a tapered cylinder. The sporophyte is dependent on the attached gametophyte for nutrients and water. Most sporophytes grow to up to 5 cm (2 inches). The thallus, or flat, gametophyte, usually lacks a midrib. The sexual organs are sunk into the upper surface of the thallus. Rhizoids (rootlike structures) on the undersurface anchor the plant. Cavities in the thallus sometimes contain colonies of the blue-green alga Nostoc.

      Hornworts differ also in having a region of continuous growth at the base of the sporophyte, and a large, irregular foot. The stalk that attaches the foot to the sporebearing capsule in liverworts is absent in hornworts.

      Hornworts reproduce sexually by means of water-borne sperm, which travel from the male sex organ (antheridium) to the female sex organ (archegonium). A fertilized egg in a female sex organ develops into an elongate sporangium, which splits lengthwise as it grows, releasing the spores that have developed within it. Elaters (elongated cells that aid in spore dispersal) are usually irregular and multicellular.

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Universalium. 2010.

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Look at other dictionaries:

  • hornwort — [hôrn′wʉrt΄] n. [after ModL Ceratophyllum: see CERATO & PHYLL] any of a genus (Ceratophyllum) of long, rootless waterlilies of the hornwort family submerged in lakes and slow moving streams and having whorls of finely divided leaves adj.… …   English World dictionary

  • Hornwort — Horn wort , n. (Bot.) An aquatic plant ({Ceratophyllum}), with finely divided leaves. [1913 Webster] …   The Collaborative International Dictionary of English

  • Hornwort — This is an article about the non vascular plants. The name Hornwort is also often applied to an aquatic plant Ceratophyllum demersum in the family Ceratophyllaceae Taxobox fossil range = fossil range|90Upper Cretaceous (but see text) to recent… …   Wikipedia

  • hornwort — paprastoji nertis statusas T sritis vardynas apibrėžtis Nertinių šeimos dekoratyvinis augalas (Ceratophyllum demersum), paplitęs Europoje, Azijoje, Afrikoje ir Šiaurės Amerikoje. atitikmenys: lot. Ceratophyllum demersum angl. common hornwort;… …   Lithuanian dictionary (lietuvių žodynas)

  • hornwort — nertis statusas T sritis vardynas apibrėžtis Nertinių (Ceratophyllaceae) šeimos augalų gentis (Ceratophyllum). atitikmenys: lot. Ceratophyllum angl. coontail; hornwort; morassweed vok. Hornblatt; Hornkraut; Igellock rus. роголистник lenk. rogatek …   Dekoratyvinių augalų vardynas

  • hornwort — noun Date: circa 1805 any of a genus (Ceratophyllum of the family Ceratophyllaceae) of rootless thin stemmed aquatic monoecious herbs with female flowers having a single carpel …   New Collegiate Dictionary

  • hornwort — noun A bryophyte with a leafless thallus characterized by a dominant gametophyte stage of the life cycle and a sporophyte stage shaped like a horn …   Wiktionary

  • hornwort — adj. grew horns, horned, betrayed by one s partner, cheated on by one s husband or wife n. plant that grows in ponds and rivers from the Ceratophyllum family …   English contemporary dictionary

  • hornwort — noun a submerged aquatic plant with narrow forked leaves that become translucent and horny as they age. [Cratophyllum demersum and related species.] …   English new terms dictionary

  • hornwort — horn•wort [[t]ˈhɔrnˌwɜrt, ˌwɔrt[/t]] n. pln any of several rootless aquatic herbs of the genus Ceratophyllum, having finely dissected, whorled leaves …   From formal English to slang

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