Botany - B.Ye. Yakubenko 2017

Part Three. Plant Kingdom (Planthae)
Chapter VII. Systematics of Higher Plants
7.4. Division Psilotophyta

The division Psilotophyta includes modern flora representatives that are phylogenetically related to fossil rhyniophytes. They are distributed in the tropics and subtropics of both hemispheres and are represented by only two genera: Psilotum and Tmesipteris. Stem branching is dichotomous, roots are absent, and rhizoids perform their Functions. Phylloids are scale-like, as in Psilotum, or green, leathery, with a central vein, as in Tmesipteris. The Internal Structure of the stem is more complex than that of rhyniophytes; beneath the epidermis, they possess cortical parenchyma, and the vascular bundle consists of phloem surrounding a actinostel (star-shaped xylem), with a pith located in the center of the stem. Sporangia fuse into synangia, and spores are homosporous. Gametophytes are often subterranean, small, and develop over several years. Fertilization is possible only in the Presence of Water.

Phylogenetically, psilophytes share certain affinities with rhyniophytes, yet they represent an evolutionary side branch, and their definitive taxonomic position within the plant kingdom remains unresolved.

Class="center">Self-Control Questions

1. When did the first land plants appear?

2. Which paleobotanist first described rhyniophytes?

3. What is the External structure of Rhynia major?

4. Which generation is dominant in The life cycle of Rhynia?

5. Why are gametophytes absent in fossil remains of rhyniophytes?

6. Name the representatives of Psilotophyta.

7. What features characterize The structure of psilophytes?



Last update: 07/08/2026

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