The Stramenopiles are a very large algal kingdom presently included in the Chromalveolata.They range in size from single-celled diatoms to giant multicellur kelp.

The definition and organization of the Stramenopiles remain disputed. They all, however, have distinctive flagella in the mobile, single-celled form found at some point in their life cycle.

Stramenopiles have two flagella of different length, one at the front of the cell, and one attached further back. The front flagellum has tiny, three-part forked brstles running along each side (called mastigonemes). This flagellum beats out a water current which moves the cell forward and food back to the cell. The rear flagella is smooth, and has a whip-like motion. (Because of these flagella, the group is sometimes called the Heteokonts - "different flagella")

Most Stramenopiles have chloroplasts surrounded by four membranes - the remnants of an anciently absorbed symbiotic eukaryote, presumably a red alga (Rhodophyta). The chloroplasts have chlorophyll a and c and usually the accessory pigment fucoxanthin, which gives them a golden-brown or brownish-green color (hence their former name Chrysophyta or Golden Brown Algae.)

Some Stramenopiles are colorless (groups Opalinata to Commation). They either branched off from the group before the absorption of the chloroplasts or else lost their chloroplasts later. (Their inclusion makes another name for this kingdom - Chromista, "colored" - irrelevant.)

They all have mitochondria and reproduce by open fission (mitosis).

The name Stramenopiles (replacing the previous Chrysophyta, Heteokonts and Chromista) means "straw-haired'. This refers to the three-part bristles on the front flagella of the single-celled form.

(TOL:This grouping of protists arose largely from molecular studies which categorically confirmed that algae (previously referred to as Heterokonts or Chrysophytes) were related to a variety of non algal protists - such as the heterotrophic bicosoecid flagellates and the fungal oomycetes (Leipe et al, 1994). The group was informally named by Patterson (1989) and was based at that time on cytological evidence. The hairs which define this group are a distinctive subset of hairs encountered in protists, and are distinguished by having a long hollow shaft that gives rise to a small number of fine hairs, and the entire structure inserts into the cell by a basal region. These hairs usually occur on the flagella. A number of supposed stramenopiles are thought (opalines) or known (diatoms) to have lost the hairs. The stramenopiles is a very major grouping of eukaryotes containing some organisms with the largest linear dimensions known in the eukaryotic world (brown algae), as well as ecologically very important organisms - such as the diatoms.)