Psilotophyta


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Related to Psilotophyta: Psilopsida, Psilophyta

Psilotophyta

(sīlō'tŏf`ətə), division of vascular plants consisting of only two genera, Psilotum and Tmesipteris, with very few species. These plants are characterized by the lack of roots, and, in one species, leaves are lacking also. The green, photosynthetic stem is well-developed. Like higher plants, e.g., the angiosperms (MagnoliophytaMagnoliophyta
, division of the plant kingdom consisting of those organisms commonly called the flowering plants, or angiosperms. The angiosperms have leaves, stems, and roots, and vascular, or conducting, tissue (xylem and phloem).
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), Psilotophyta has specialized conducting, or vascular, tissue (xylem and phloem). Psilotum, with only two species, is widespread in tropical and subtropical areas, whereas Tmesipteris species is restricted to Australia and neighboring islands. The spore-producing structures are produced in clusters in the axil of a leaflike at the end of a short lateral branch. The gametophytegametophyte
, phase of plant life cycles in which the gametes, i.e., egg and sperm, are produced. The gametophyte is haploid, that is, each cell contains a single complete set of chromosomes, and arises from the germination of a haploid spore.
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 plant, arising from germination of a spore, is small and colorless, and derives its nutrition through a specialized association with a fungus. Sexual structures on the gametophyte produce eggs and sperm. The motile sperm, with numerous flagella, are able to swim through a film of water to the egg. The fertilized egg, or zygote, first absorbs nourishment from the gametophyte, and later becomes photosynthetic and self-sustaining. The life cycle is very much like that of fernsfern,
any plant of the division Polypodiophyta. Fern species, numbering several thousand, are found throughout the world but are especially abundant in tropical rain forests. The ferns and their relatives (e.g.
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.

Psilotophyta

 

a division of ancient vascular plants that includes one order—Psilotales. The plants are sometimes considered to be a class (Psilotopsida). The Psilotophyta are small rootless plants that are epiphytic or grow on humus-rich soil and in rock crevices. The underground rhizomatous organs contain fungous hyphae (endotrophic mycorrhiza). The stems are covered by an epidermis with stomata that are structurally similar to the primitive stomata of fossil Rhyniaceae.

The Psilotophyta include two genera, Psilotum and Tmesipteris, which have polymorphous species and are usually combined into the family Psilotaceae. There are two species of Psilotum, each having small scalelike leaves and repeatedly dichotomously branching stems that are 20–100 cm long. Both species are found in the tropics and subtropics of both hemispheres. The genus Tmesipteris also has two species, whose stems measure 5–40 cm long and bear well-developed blades (sporophylls) in the upper portion. The Tmesipteris are found primarily in Australia, Tasmania, New Zealand, and Polynesia.

The synangia that form on the Psilotophyta are bilocular or trilocular. The spores, as they sprout, give rise to underground gametophytes that lack chlorophyll and live saprophytically on fungi. The gametophytes do not differ from the young rhizomatous organs in size and form.

REFERENCE

Takhtadzhian, A. L. Vysshie rasteniia, vol. 1. Moscow-Leningrad, 1956.

M. E. KIRPICHNIKOV

Psilotophyta

[‚sī·lō′täf·əd·ə]
(botany)
A division of the plant kingdom represented by three living species; the life cycle is typical of the vascular cryptogams.