Phaeophyta 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 kelps are abundant – as large “rafts” of floating Sargassum. (Lee, 1999).

“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).

The Phaeophyta 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)

brown algae is prey of:
Nereis diversicolor
Nereis virens

Based on studies in:
Scotland (Estuarine)

This list may not be complete but is based on published studies.

There are three general types of life history among the Phaeophyta: isomorphic alternation of generations, heteromorphic alternation of generations, and diplontic (see diagrams among images). (Graham & Wilcox, 2000)

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).

This is still debated. Some algal biologists (phycologists) classify Phaeophyta as a phylum (aka "division") within the plant kingdom, others put it in the kingdom Chromista, and some still classify it among the protists.

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)