Pennsylvanian phylloid algal reefs are widespread and well exposed in south Guizhou, China. Dense networks of closely living phylloid algae induced community restriction on seafloor and organisms seldom survived in such environment. Algal reefs in Guizhou differ from examples reported to date by high biodiversity. This contrasts to the “poisoning hypothesis” and chemical defense was not pronounced. Phylloid algae were able to thrive over a large depth range. Delicate framework formed by upright blades often occurred in calm deepen waters. Blades became larger and fleshy in moderately agitated environment and formed isolated, wide, cup-shaped framework. Large blade size could capture much more sunlight to improve rate of growth and calcification. But successive progressively shallower water may have arrested phylloid algae growth. Thinner, small blades grew closely packed and juxtaposed near and above one another in a wave-dominant environment, producing dense framework clusters to prevent wave destruction.