I. SYNONYMS: Brown algae, phaeophyta.

II. NUMBER: >900 species (250 genera).

III. PHYLUM CHARACTERISTICS:

• A. Structure and Physiology
  • Cell Form: Filamentous, thalloid or multicellular to 50m long.
  • Flagella: Two flagella; recurrent (text with tooltip) Recurrent flagella bend to the posterior end of the cell. Typically, they are identified as recurrent when anteriorly-directed flagella are present. or posterior whiplash (text with tooltip) (1) A whiplash flagellum is a eukaryotic 9+2 flagellum with few or no flagellar hairs or scales. These may be directed anteriorly or posteriorly. (2) A whiplash flagellum is free of hair-like mastigonemes and usually is trailing or posteriorly-directed. and anterior (text with tooltip) An anteriorly-directed flagellum extends in the direction of the motion of the motile cell. The interpretation is that the flagellum functions by pulling the cell. tinsel (text with tooltip) A tinsel flagellum is one that is covered with flagellar hairs and thus appears thicker in light microscopy. Usually, tinsel flagella are anteriorally-directed. .
  • Basal Bodies: Basal bodies (text with tooltip) Basal bodies (also called kinetosomes) are organelles that are not membrane-bound. All eukaryotic flagella (also called undulipodia) are underlain or attached to the cell by the basal body. The basal body is a microtubular structure with the general formula 9(3)+0. They are indistinguishable from centrioles. perpendicular (with striated (text with tooltip) Striated roots (also called kinetodesma, banded roots, kinetodesmal fibers, or striated fibers) are banded flagellar roots that elaborate from basal bodies. They form a distinctive and diagnostic network in the Ciliata. rhizoplast (text with tooltip) A rhizoplast is a striated root system that extends from the basal body tinto the cell, usually to the nuclear envelope. ?)
  • Cell Covering: Cells surrounded by a thick, mucilaginous ( alginic acid (text with tooltip) Alginic acid (n.) is a polysaccharide characteristic of the phaeophytes. It can be up to 40% of the dry weight of the organism. ) cell wall.
  • Chloroplasts: Chloroplasts are yellow-brown with chlorophylls a and c1 and c2 (text with tooltip) Chlorophyll C is a variant of Chlorophyll A. and a secondary photosynthetic pigment in the many of the photosynthetic heterokonts and dinoflagellates. ; also with B-carotene, large amount of fucoxanthin (text with tooltip) Fucoxanthin is a carotenoid secondary photosynthetic pigment that occurs in many of the photosynthetic eukaryotes like the heterokonts and haptotists. and other xanthophylls (text with tooltip) Xanthophyll is an oxygenated carotenoid secondary photosynthetic pigment that occurs in many of the photosynthetic eukaryotes. .
  • Food Reserves: Laminarin (text with tooltip) Laminarin is a photosynthetic storage product of phaeophytes. .
  • Mitochondria: Tubular cristae (text with tooltip) Mitochondrial cristae that form as extended saccate structures or tubes are called tubular cristae. .
  • Golgi: Present and next to the nucleus.
  • Nucleus: Uninucleate cells.
  • Centrioles: Centrioles (text with tooltip) Centric (adj) describes a type of diatom that is radially symmetrical. It also describes nuclear division in which centrioles are present. present; some reports of astral rays.
  • Inclusions and Ejectile Organelles:
  • Not present.

• B. Mitosis, Meiosis and Life History
  • Mitosis: Variable; usually, the nuclear membrane breaks down at least a spindle poles (open mitosis).
  • Meiosis: Present.
  • Sexual Reproduction and Life History: There is usually an alternation (text with tooltip) A life cycle exhibits alternation of generation when it involved the alternation of haploid (gamete-producing) and diploid (spore-producing) phases. of haploid gametophyte (text with tooltip) A gametophyte is haploid, gamete-producing phase of an organism that exhibits alternation of generation. and diploid sporophyte (text with tooltip) A sporophyte is the diploid phase of an organism that exhibits alternation of generation. This phase produces spores usually in specialized sporangia as the immediate products of meiosis. generations, that may be isomorphic (text with tooltip) Isomorphic alternation of generation occurs in organisms in which the haploid gametophyte phase and diploid sporophyte phase are indistinguishable in form. or heteromorphic (text with tooltip) Heteromorphic alternation of generation occurs in organisms in which the haploid gametophyte phase and diploid sporophyte phase are different in form. . Asexual reproduction is by biflagellate zoospores (text with tooltip) A zoospore is an asexual spore that is motile. Zoo- (pronoumced zo-o) is a prefix that means moving. and sexual reproduction involves two biflagellate gametes ( isogamy (text with tooltip) Isogamous (adj) describes sexual reproduction in which the gametes are structurally identical. or anisogamy (text with tooltip) Anisogamous (adj.) describes sexual reproduction in which the gametes are structurally siimilar, but not identical. ) or oogamy with biflagellate spermatozoids and larger oogonia. Taxa that are large in the diploid or sporophyte phase usually cluster the meiosporangia into a region on the thallus, such a cluster of sporangia is called a sorus.
    • Ectocarpus life cycle.
    • Laminaria life cycle.
    • Fucus life history.

• C. Ecology: Mainly found in the intertidal zone, but the giant kelps are subtidal.