I. Characteristics

A. Multicellular, branching filaments
B. Cell wall with inner cellulose layer, gelatinous pectic layer containing algin.
C. Motile cells with 2 different flagellae
D. Chloroplasts with high proportion of carotenaids to chlorophyll.(a and c) several xanthophylls includiog fucoxanthins. Chloroplasts variable, but usually discoid.
E. Food reserves laminarin & mannitol, sometimes fats

III. Structure

A. Size - few are microscopic, most much larger - up to 150' . Larger forms with complex structure.
B. Cell wall - "Algin" - outer pectin layer is major component
C. Tissues - some specialization seen here. Tissues are groups of similar cells with similar function.  Tissues with essentially similar cells - simple tissues, different types of cells contribute to similar function - complex tissues. Groups of tissues making up a morphologically and often functionally distinct part of organism - organ. Many brown algae have different tissues & have stem-like, root-like, leaf-like organs. Since they do not have vascular systems, these structures are not true stems, roots, or leaves. Termed rhizoid, stalk or stipe, caulalia, and phyllidia. Tissues which are relatively unspecialized- parenchyma. Usually thin-walled, often isodiametric. Most photosynthetic tissues are of this kind. Tissue char. by cell division - meristem.

General life cycle-
 

One class, including Fucus has the gametophyte generation greatly reduced, and not an independent plant.

V. Representative genera.

A. Ectocarpus
    Commonly found as an epiphyte of larger brown algae. Often very much branched. Isomorphic alternation of generation, L.c. essentially as above.
B. Laminaria - kelp
    Mature sporophyte with distinct holdfast, stipe & blade.
Stipe erect, unbranched, XS with 3 parts
    1. medulla, - some cells of which are conducting cells.
    2. Cortex - with mucilaginous cells.
    3. Epidermis.
Sporangia produced on both surfaces of blade - n zoospore - 32 or 64 - microscopic gametophytes, 1/2 zoosp. - Male gametophyte, 1/2 - female gametophyte syngamy - zygote - sporophyte. (Heteromorphic alt. of gen.)
C. Macrocystis - giant kelp.
D. Nereocystis
E. Postelsia palmiformis - Monterey
F. Fucus
    Diploid thallus, gametophyte essentially non-existent. Only haploid portion - "gametes" - actually spores acting as gametes. Sporangia or gametangia borne in conceptacles scattered over receptacles,
G. Sargassum
    tropical & subtropical. Attached or freefloating. Sargasso Sea L.C. Similar to Fucus

A. Fertilizer
B. Burn, recover potassium & iodine No longer profitable.
C. Food - esp. Japan
D. Source of algin - stabilizer & moisture retainer in many products such as ice cream, cake frosting, paint, pharmaceutials, & processing of natural & synthetic rubber.