17.5: Phaeophyta - The Brown Algae

Brown algae are brown due to the large amounts of carotenoids they produce, primarily one called fucoxanthin. These organisms are exclusively multicellular and can get so large that they require special conductive cells to transport photosynthates from their blades down to the rest of their tissues. These conductive cells are called trumpet hyphae and have sieve plates and resemble sieve tubes found in flowering plants. You may not see these, but be on the lookout for them!

• Morphology: Multicellular thallus
• Cell wall composition: Cellulose
• Chloroplasts: 4 membranes, pigments are chlorophyll a, chlorophyll c, and fucoxanthin
• Storage carbohydrate: Laminarin
• Life cycle: Diplontic
• Ecology: Marine

View the variety of brown algae on display. In the space below, label the morphology of a brown algal thallus. Much like Saprolegnia, the body of an alga is termed a thallus because it is not differentiated into specialized tissues. Label the holdfast, stipe, gas bladder(s) [also called a float], and blade(s).

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