Hornwortdivision Anthocerotophytaalso called horned liverwortany of about species of small nonvascular plants. Hornworts usually grow on damp soils or on rocks in tropical and warm temperate regions. The largest genusAnthoceroshas a worldwide distribution. Dendroceros Hornwort asexual reproduction Megaceros are mainly tropical genera. Hornworts have an ancient lineage and are thought to be some of the earliest plants to have evolved on land.
The plant bodies of liverworts and hornworts represent the gametophytic sexual phase of the life cycle, which is dominant in these plants. In the liverworts, the sporophyte is borne upon or within the gametophyte but is transitory.
Liverwort and hornwort plants, depending on the…. Traditionally, hornworts have been classified as bryophytestogether with mosses division Bryophyta and liverworts division Marchantiophyta.
In some classification systems, hornworts have been grouped as horned liverworts in the Hornwort asexual reproduction Anthocerotidae class Hepaticaeclass Anthocerotopsida, order Anthocerotales.
However, molecular evidence suggests that hornworts have an evolutionary history distinct from both mosses and liverworts, and the plants are now placed in their own taxonomic division, Anthocerotophyta. The classification of the group remains controversial, and the number of hornwort families, genera, and species is under revision.
The sporophyteor 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 thallusor flat, gametophyte, usually lacks a midrib.
Hornwort asexual reproduction 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 from other bryophytes 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 spore-bearing capsule in liverworts is absent in hornworts.
Hornworts reproduce sexually by means of waterborne spermwhich travel from male sex organ antheridium to the female sex organ archegonium. A fertilized egg in a female sex organ develops into an Hornwort asexual reproduction 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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The Editors of Encyclopaedia Britannica. Anthocerotae, Anthocerotophyta, Anthocerotopsida, horned liverwort. Learn More in these related Britannica articles: Anthocerotophyta hornworts Gametophyte thalloid, with Hornwort asexual reproduction single large chloroplast per cell, mucilage cavities present; sporophytes persistent, erect hornlikephotosynthetic, arising from upper surface of gametophyte, possessing stomata, columella, basal meristem, and pseudoelaters opening by 2 valves but lacking an operculum; representative genus, Anthoceros.
The gametophyte is a small ribbonlike thallus that resembles a thallose liverwort. The name hornwort is derived from the unique slender, upright sporophytes, which are about 3—4 cm 1. Hornwort s are unusual among the bryophytes because the sporophyte has indeterminate growth.
This means that throughout the growing season new tissue is continually produced, even when spores are being shed. Early in its Hornwort asexual reproduction within the archegonium, the embryo produces a foot that penetrates the…. More About Hornwort 5 references found in Britannica articles Assorted References annotated classification In bryophyte: Annotated classification In plant: Annotated classification characteristics In bryophyte: Form and function description In plant: Division Anthocerotophyta system of reproduction In plant reproductive system: Help us improve this article!
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