Figure 1.

Heterostyly in Primula: (A) Diagrams of short‐styled (S‐) and long‐styled (L‐) morphs of distylous Primula sp., with sexual organs placed reciprocally at two levels in the corolla tubes of compatible, heteromorphic flowers (i.e., reciprocal herkogamy). Photographs of S‐ and L‐morphs of (B) Primula elatior and (C) Primula vulgaris. High anthers of S‐morphs match the position of high stigmas in L‐morphs, and low anthers of L‐morphs match the position of low stigmas in S‐morphs (i.e., sexual organ reciprocity between exposed and sunken organs, respectively; solid arrows). Conversely, incompatible sexual organs of the same flower or floral morph (i.e., homomorphic) do not match spatially (dashed and dotted arrows, respectively). Distyly promotes pollen transfer between heteromorphic, compatible flowers (i.e., disassortative pollination). Photograph (B) courtesy of Florian Boucher; the others were taken by the first author in natural Swiss populations.