Explain thallus organization in phaeophyta and comment on life cycle pattern in rhodophyta.
Answers
Phaeophyta (fá-O-fa-ta) is made of two Greek roots that mean brown (phaios -φαιός); and plant (phyto -φυτό). The reference is to the dominance of the brown accessory pigments that give the thalli a tawny to dark brown appearance. Kjellman (1891) originally coined the class, Phaeophyceae. The emergence of the class as a separate phylum called for changing the name to Phaeophyta, as it appears in Margulis and Schwartz (1998).
INTRODUCTION TO THE PHAEOPHYTA
The brown algae are the dominant producers in northern temperate and arctic intertidal waters. They range in form from microscopic branched filaments (Figure A), to pseudoparenchymatous and cortical thalli (Figures 2-5), to enormous multicellular parenchymatous kelps (Figures 6-7), and like plants, those at the multicellular end of organization tend to be diploid in their dominant form (usually sporophyte). Some exhibit apical growth (8-11). Fucus and similar taxa have lost the gametophyte entirely and have gametic meiosis (Figures 12-13). Most of the phaeophytes, particularly the kelps, exhibit a heteromorphic alternation of generation.
FILAMENTOUS AND PSEUDOPARENCHYMATOUS TAXA
These taxa all have the same growth form but are not related to each other. In general, they are relatively small as the phaeophytes go, and all form branched filaments. Some of the branched filaments are relatively simple with a single main filament from which lateral branches arise. However, many taxa are made of branched filaments that are woven into a three dimensional structure, usually a tube or flat blade. This more complex condition is called pseudoparenchymatous. though some are pseudoparenchymatous. Most taxa in this group exhibit trichothallic growth, that is cell division occurs in certain well-defined areas of the filament. Because the filaments do not grow from the the tips, these taxa are able to withstand heavy grazing pressure, especially by sea urchins.