Variation in Heterostylous Reproductive Systems Among Populations of Oxalis alpina in Southeastern Arizona

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Abstract
Numerous stages in the evolution of distyly from tristyly may be observed among populations of O. alpina in southeastern Arizona. At one extreme, the mid form is common in populations and features of floral morphology are similar to those of typical trimorphic species. At the other extreme, the mid form is absent and few of the morphological features of tristyly are retained. A spectrum of populations with intermediate mid frequencies and floral morphology connects these extremes. Modifications of style form representation and floral morphology are consistent with those expected in populations where modified incompatibility results in selection against the mid form. Disjunction of populations and variation in evolutionary rates probably resulted in the diversity of intermediate reproductive systems occurring in this region.