homogeneous / homogenous
Uniform versus related by origin.
Homogeneous means of one kind throughout: a homogeneous sample. Homogenous is the biological word for structures that share an origin. Homogenous also turns up as a loose spelling of homogeneous. If you mean uniform, use homogeneous.
Examples
Use a homogeneous group
Avoid a homogenous group (If you mean only that the group is uniform.)