Algae are actually plants that do not have roots, stems, leaves, flowers, et cetera. However, the variety that grows on roofs relies on the sun, moisture, and the shingles to provide sustenance for their growth. Since asphalt shingles are made of limestone, algae have ample supply of food from these shingles. The most common type of algae that grow on roofs is gloeocapsa magma.
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