"Tommies"(Crocus tommasinianus) naturalize happily in short grass and under deciduous trees (and in pots on my window sill). They're sometimes called the Woodland Crocus but they need the sun on them for the flowers to unfurl and reveal the bright orange anther dusted with pollen.
 They range in colour from a rare white form through silvery shades of violet into deeper tones of pink and purple. They have an ethereal quality but they're tough: flowering in February they can withstand the last throes of winter.