Cell wall: generally contains cellulose (1-10% of thallus dry-weight), alginic acid, and sulfated polysaccharides
Plastids: varies among genera – may be from one to many per cell; typically have a girdle lamella; have a periplastidal endoplasmic reticulum, which is continuous with the nuclear envelope
Pigments: fucoxanthin, which gives the algae their characteristic greenish-brown color; chlorophyll a; chlorophylls c1 and c2; beta-carotene; and violaxanthin
Photosynthetic reserve product: laminarian
(Lee, 1999; Graham & Wilcox, 2000)
There are three general types of life history among the Phaeophyaceae: isomorphic alternation of generations, heteromorphic alternation of generations, and diplontic (see diagrams among images). (Graham & Wilcox, 2000)
“There are no unicellular or colonial organisms in the order, and the algae are basically filamentous, pseudoparenchymatous, or parenchymatous.” (Lee, 1999)
See also: algaebase.org Phaeophyceae
Visible thalli range from a few centimeters to over 45 m (150 ft), depending on species and environmental conditions. The gametophytes of species with heteromorphic alternation of generations are microscopic. (Connor & Baxter, 1989).
Phaeophyceae are nearly all marine and most occur on rocky substrates in the upper littoral zone and the low to mid intertidal. There are only four genera with freshwater species, however, several marine taxa can also occur in the brackish water of saltmarshes. (Lee, 1999)
Phaeophyceae can dominate the rocky subtidal and intertidal of temperate regions, where, though the species diversity is lower than that of the red algae, their numbers are much higher. The “Sargasso Sea” is the only area in warm waters where Phaeophyceae is abundant – as large “rafts” of floating Sargassum. (Lee, 1999).
Sexual and vegetative, with three general life history classes: isomorphic alteration of generations, heteromorphic alternation of generations, and diplontic. Populations occurring in brackish waters have almost totally lost their ability for sexual reproduction. Their primary method of propagation is vegetative.
(Lee, 1999; Graham & Wilcox, 2000).
Evolution and Systematics
Systematics and Taxonomy
This is still debated. Some classify Phaeophyceae as a phylum (aka “division”) within the kingdom Plantae, whereas others place it in the taxonomically narrower kingdom “Chromista.” Some algal biologists use the term “Phaeophycean” and place that in the higher taxon “Ochrophytes.” Others classify Phaeophyceae within the “Heterokontophyta.”