[2] Crucigenia consists of colonies of four cells in a flattened square shape, up to 16 μm in diameter; occasionally these colonies may be joined together to form 8- or 16-celled compound coenobia.

Cells are triangular, ovoid, ellipsoid, or rectangular, forming a small hole in the center of the colony.

It was first described by Charles François Antoine Morren in 1830 containing the type species C. quadrata, but then renamed Staurogenia by Friedrich Traugott Kützing without an explanation; later the name Crucigenia was noted to be the correct name.

[3] The genus Tetrastrum, unlike Crucigenia, may have spines or warts on its cell walls.

[5] Species are distinguished from each other by the cell shape, and whether a pyrenoid is absent or present.