Stramenopiles

    Stramenopiles are a diverse group of eukaryotic organisms grouped together largely on the basis of recent molecular studies. Stramenopiles include the water molds (Division Oomycota), the golden algae (Division Chrysophyta), the diatoms (Phylum Bacillariophyta), the brown algae (Division Phaeophyta), and several other groups of organisms. Information on each group is presented below.

Water molds

    Approximately 580 species of water molds or oomycetes are known. The vegetative stage of water molds is typically fungus-like in appearance and is composed of coenocytic hyphae. Cells walls are primarily composed of cellulose. Flagellated cells, when present, are generally biflagellate. Water molds, as their name implies, commonly occur in water or damp soil and are often important decomposers in aquatic systems. Some oomycetes are plant parasites, with notable examples including the organisms responsible for downy mildew of grapes (Plasmopara viticola) and late blight of potatoes (Phytophthora infestans). Others occur as saprobes and animal parasites.

Golden algae

    The chrysophytes are named for their characteristic golden color, which results from large amounts of yellow and brown carotenoids which often mask chlorophylls a and c. Golden algae are autotrophic and can be unicellular, colonial, or filamentous. Cell walls, when present, are composed of cellulose, often with a silica component. The storage material present in the golden algae is chrysolaminarin. Approximately 850 species of golden algae are known.

Diatoms

    Almost all of the approximately 10,000 species of diatoms are unicellular, although there are some colonial and filamentous forms. Members of Phylum Bacillariophyta have distinctive cell walls composed largely of silica that are divided into two halves. Diatoms are abundant in both freshwater and marine environments and are important primary producers in the phytoplankton.

Brown algae

    The brown algae are the most complex members of the stramenopiles. They are exclusively multicellular and most occur in marine environments. The brown algae contain large amounts of brownish carotenoids in addition to chlorophylls a and c. Cell walls are composed of cellulose and large quantities of various phycocolloids. Members of this group are filamentous, membranous, or plant-like in appearance and range in size from relatively small to very large.

Points to remember:

• Stramenopiles are a group based mainly on molecular studies and include the water molds, golden algae, diatoms, and brown algae, to name a few.
• Water molds are fungus-like in appearance and occur in aquatic or damp terrestrial environments.
• Golden algae are autotrophic organisms characterized by the presence of yellow and brown carotenoid pigments.
• Diatoms are extremely important primary producers in phytoplankton and occur in fresh and marine water.
• Brown algae are complex, mostly marine organisms that range in size from diminutive forms to very large forms.

Representative organisms:

Water molds

•  Plasmopara (provided courtesy of Tom Volk, University of Wisconsin La Crosse)

Golden algae*

• Dinobryon
• Chrysosphearella longispinum

*Golden algae images were taken from the Susquehanna University Algal Image Archive.

Diatoms**

• Fragillaria pinnata
• Cymbella minuta
• Selaphora pupula

**All diatom images were taken from Bowling Green State University Center for Algal Microscopy and Image Digitization.

Links:

• The Tree of Life shows the phylogeny of the stramenopiles and has a more complete listing of the organisms contained within this grouping.
• The University of California at Berkeley Museum of Paleontology has an informative page describing some of the stramenopiles.
• Click here for pictures and other information regarding brown algae (Division Phaeophyta).