The kingdom protista contains a variety of different organisms,
ranging from animal-like to fungi-like. These organisms have all been included
to the same taxonomic kingdom for their simple construction, and most are
unicellular species. Algae used to be classified with plants because they
have chlorophyll a, they are plantlike and photosynthetic. But
they have since been moved to Protista because of their simple construction,
the broad range of photosynthetic pigments they use, the lack of protective
tissue surrounding their "naked" gametes, and their highly varied
life histories.The algae are considered primitive photosynthetic organisms
based on their reproduction and simplistic construction. Algae have been
found in the fossil record as early as 590 million years ago for macroscopic
algae, and 1900 million years ago for microscopic algae.
Motile cells are heterokonts; their two flagella are
of unequal length and differing morphologies. The brown algae are
placed into one class: Phaeophyceae. Their distinguishing characteristics
are outlined within the class.
The class Phaeophyceae contains 265 genera and over 2000 species,
of which 99% are marine organisms. The brown algae are distinguished
by a suite of characteristics including the following:
Photosynthetic pigments: chlorophyll a and c,
beta carotene, violaxanthin, and fucoxanthin.
Food reserves: laminaran,
a soluble polysaccharide, and mannitol, a sugar-alcohol.
Cell construction: cellulose
fibers bound with alginic acid form cell walls,
Chemistry: presence of soluble
extract, fucoidans, which are sulfated polysaccharides.
Reproduction: most are haplobiontic,
except the diplontic, oogamous Fucales
Reproduction: diplontic, oogamous life history, with unique sperm
morphology (anterior flagellum is shorter and pleuronematic).
Cell construction: chloroplasts
Contains as many as 17 genera.
Cell construction: single
apical cell terminates each axis; three-sided
apical cell (thought to be a more primitive,
Reproduction: formation of
one ova per oogonium.
Characterized by highly differentiated basal and apical regions; presence
of catenate pneumatocysts.
Characterized by chains of pneumatocysts on terminal
apical fronds and bipinnate branching of basal blades.