Introduction to the Chromista

From microbes to giants. . .

It may seem hard to believe that microscopic diatoms, with their delicate silica skeletons only forty millionths of a meter long, can be related to the giant kelps, which may grow as long as fifty meters, or that either one is related to the downy mildew that nearly destroyed the French wine industry. But they are related -- placed together in the great kingdom-level taxon Chromista.

The name Chromista means "colored", and although some chromists, like mildews, are colorless, most are photosynthetic. Even though they are photosynthetic, chromists are not at all closely related to plants, or even to other algae. Unlike plants, the Chromista have chlorophyll c, and do not store their energy in the form of starch. Also, photosynthetic chromists often carry various pigments in addition to chlorophyll, which are not found in plants. It is these pigments which give them their characteristic brown or golden color.

Photosynthetic chromists are some of the most important organisms in aquatic ecosystems. The cool and temperate coasts of continents are lined with kelp forests, where many commercially important fish and shellfish feed and reproduce, and diatoms are frequently the primary source of food for both marine and fresh-water organisms.

In additional to their roles as producers for marine animals, chromists provide many products for industry. Alginates are viscous chemicals extracted from kelp; these are used in paper production, toothpaste, and in ice cream, where the alginate helps to improve texture and ensure uniform freezing and melting. Ancient chromists, like coccolithophorids, are responsible for deposits of limestone and other rock formations. The skeletons of dead chromists accumulate on the floor of lakes and oceans, where they may become thick deposits of silica or calcium carbonate. These deposits are useful for interpreting ancient climate, and in searching for oil.

Click on the buttons below to learn more about the Chromista.

You can navigate deeper into the Chromista groups by selecting Systematics!

Visit the Tree of Life for a current cladogram showing the relationships among the chromists, also known as stramenopiles.

More pictures of diatoms are available at the Algal Microscopy and Image Digitization server at Bowling Green State University.

For a fuller listing of on-line phycological collections resources, try our Phycological Collections Catalogs Listings.

Images of kelp and Saprolegnia courtesy Wisconsin; coccolith image courtesy Dr. William Ruddiman and the US National Geophysical Data Center; picture of Odontella taken by Karen Wettmore.