Fundamentals of Evolution - Korzh O.P. - 2006

Part III. PATHS OF LIFE EVOLUTION

Chapter 19. Main Directions of Living Organisms Evolution

19.3. Bryophytes as an Evolutionary Dead End in Higher Plants

Bryophytes are considered a rather distinct, evolutionary blind branch of higher plants whose general Organization approaches that of Algae. They carved out their specific ecological niche long ago and maintain it to this day without any loss of morphological and biological diversity amidst the complex conditions of continental formation, climate change, and shifting vegetation cover.

The distinctiveness of bryophytes lies in the specifics of their life cycle: Morphology/12.html">ALTERNATION OF GENERATIONS differs from that of vascular plants in that the gametophyte expands its role beyond sexual reproduction, taking over the primary vegetative Functions as well (Photosynthesis, Water supply, mineral Nutrition, etc.). Conversely, the sporophyte is practically limited to spore production alone.

The oldest representatives of bryophytes—thalloid liverworts of the order Metzgeriales—are recorded from the Devonian. Marchantiales and true mosses (Bryidae) appear in the Carboniferous, while Ricciales, Sphaerocarpales, and Sphagnales emerge in the Jurassic period.

The vast majority of bryophytes are perennial plants, yet despite their longevity, all of them are low-growing. This group is characterized by a relatively simple external and internal organization: dermal, mechanical, storage, and conducting Tissues are quite weakly expressed (or untraceable in some groups), and specialized vegetative Organs are practically absent (though leaves and stems can be conditionally distinguished in certain groups). This is explained by the fact that the structural capabilities of the gametophyte are more limited compared to the sporophyte, resulting in poorly developed vascular systems and restricted upward growth.

THE ORIGIN OF bryophytes remains a subject of debate, as no intermediate forms between them and other modern higher plants have yet been found. Consequently, the prevailing view today is that bryophytes evolved directly from algae (ancient green algae) independently of other plants. This hypothesis, supported by R. Wettstein, D.K. Zerov, and others, is corroborated by data from various biological fields, particularly the presence of shared biochemical, cytological, and genetic features: identical chlorophylls a and b, similar carotenoids, starch, Cellulose-pectin Cell walls, and so on.

However, the similarity in sex organs and sporangia found in most seedless plants contradicts this view. Therefore, some botanists suggest a common origin for bryophytes and vascular plants. For instance, a hypothesis has been proposed suggesting that bryophytes originated from rhyniophytes As a result of the general reduction of the sporophyte and the Progressive development of the gametophyte (B.M. Kozo-Polyansky, A.L. Takhtajan, et al.). In this case, sporophyte reduction is considered a consequence of bryophyte adaptation to specific environmental conditions—high humidity.