Euastrum crassum is a freshwater green algae characterized by its polygonal shape, often resembling a star or cross, with cells typically ranging from 50 to 100 micrometers in diameter. Each cell features a thin and smooth cell wall and contains multiple disc-shaped chloroplasts arranged radially within. Reproduction primarily occurs through binary fission, producing genetically identical daughter cells. It inhabits freshwater habitats such as ponds and lakes, where it attaches to submerged surfaces via a holdfast or stalk structure. Euastrum crassum contributes to aquatic ecosystems by photosynthesizing and serving as a source of food for various aquatic organisms.