Most of the species can be found in Mexico, five in the Southwestern United States, and three are scattered in Colombia and Brazil.

[13] Other authorities, however, maintain that this is in error, that the name comes from Melampus, a soothsayer of renown in Greek mythology.

[5] The genus consists of annuals and perennials or bushy plants, growing to a height of 1 m. When fully grown, they tend to fall over.

[5] The numerous fruits are seed-like (they consist of inner involucral bracts each enclosing and fused with individual ray achenes), with a few narrow scales at their tip.

They make this genus one of the most prolific of the summer annuals, with seedlings coming up constantly.