Alsike clover is not nearly as common as Red Clover (Trifolium pratense) or White Clover (Trifolium repens). It does look rather like a cross between the two; Linnaeus thought it was, which is why it is saddled with the species name hybridum. The bicolored flower heads make this a very decorative plant. This patch was blooming May 30 in South Side Park.
For a more detailed description, see the Trifolium hybridum reference page.