The pollen of most of the approximately 140 species ofLinumhas now been examined. Most have tricolpate pollen, but nineteen have been found to have multiaperturate pollen. These are distributed among three of the five subgenera usually recognized in the genus, and almost certainly are the result of three independent evolutionary routes. There is evidence that the multiaperturate condition may have evolved twice in each of two of these subgenera. It is possible, if not probable, therefore, that species with multiaperturate pollen may have evolved from those with triaperturate pollen on as many as five different occasions in this genus.