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Turtle grass, Thalassia sp., is one of the very few true marine plants. Although not found on reefs, back-reef areas may have beds of turtle grass, which nourish crustaceans and juvenile fishes as well as the dugong.

The marine algas Udotea (top) and Halimeda can both be occasionally found on the reef. Udotea is only lightly calicified, but the calcium carbonate disks of Halimeda are in some areas a major component of the reef substrate.

On the reef, however, despite its teeming life, plants seem absent. In fact, plants are the primary producers on the reef, just like every other environment. Most of the algae found on the reef grows as a short "turf," a fine carpet of hairs that is a mix of dozens or hundreds of species of brown, red and green algaes. While diving, look closely at an area of bare coral rock and you will probably see a fine carpet of "hairs" growing on it.

The algal turf grows at a prodigious rate, but a herd of grazers—tangs, parrotfish, damselfish, sea urchins, snails and many others—keeps it clipped short. If an area of reef were caged off to prevent the entry of herbivores, the turf would quickly sprout into a thicket. The farmerfish damsel (Stegastes lividus) does just this, by force of personality keeping out all intruders from his own luxurious green patch of hair algae.