Progymnosperm
Radial section of the wood of Archaeopteris ( bar = 1 mm).
The Progymnospermen are a group of vascular plants that mediate in their characteristics between the ferns and seed plants. Today they are regarded as the group of plants from which the seed plants have developed.
Features
The Progymnospermen usually had a shrubby to tree-like growth habit. Your branch was pseudomonopodial, but they did not form axillary buds. They wore either dichotomously branched units or flat leaves with dichotomous venation.
The organization of the vascular system ranged from a protostele to a Eustele with mesarcher Xylemreifung (from the center of the primary xylem in both directions). They had a bifaziales cambium that produced secondary tissue. The secondary xylem is pyknoxylisch and consists of tracheids with bordered pits and rays. In order for the wood resembled the extant conifers.
The Progymnospermen formed spores. These have sporangia that were formed along the adaxial or lateral side of lateral branches or modified leaves. There are both isospore and straight spore representative.
Systematics and evolution
The Progymnospermen likely to have evolved from the Trimerophytophyta that dreirippige protostele the early representatives resembles the Trimerophyta.
The Progymnospermen following orders are counted:
- Archaeopteridales Archaeopteris
- Tetraxylopteris
The Progymnospermen be adopted today generally considered the progenitor of the seed plants. There are, however, there are two main theories:
- Rothwell assumes that the monophyletic seed plants from an ancestor that matches the Aneurophytales descended.
- Beck assumes that the seed plants have emerged diphyletisch: the seed ferns would thus descended from the Aneurophytales, Cordaitales and conifers of the Archaopteridales.
History of Research
The Progymnospermen as spore-forming plants with conifer -like wood were recognized only in 1960 by Charles E. Beck as such, as he could put together the hitherto known only separated wood and leaves of the plant now known as Archaeopteris.
Documents
- Thomas N. Taylor, Edith L. Taylor: The Biology and Evolution of Fossil Plants, pp. 440, 459 Prentice Hall, Englewood Cliffs, 1993 ISBN 0-13-651589-4.