Mapping is provisionsal. This widespread annual weed from Eurasia has several segregates or close allies that need more assessment in Ky. (2n = 40, 60). Although treated recently as subspecies for FNA 5, some of these taxa have often been considered species, and there is little or no intergradation in many areas. Those reported from Ky. are P. arenastrum (= aviculare ssp. depressum (Meisner) Arcangeli); P. bellardii (= aviculare ssp. neglectum (Besser) Arcangeli); and P. buxiforme (= aviculare ssp. b. (Small) Costea & Tardif); see notes under those names. Most records of aviculare should probably be transferred to arenastrum.