Figure 1.- Heterostyly and homostyly in Primula vulgaris. Heterostylous floral morphs can be either short-styled (S-morphs) or long-styled (L-morphs). They are characterized by reciprocal placement of male (anthers) and female (stigmas) sexual organs (i.e., reciprocal herkogamy), promoting outcrossing. Additionally, a physiological self-incompatibility mechanism prevents self- and intramorph fertilization. Homostylous floral morphs (H-morphs) are characterized by reduced or no herkogamy and are self-compatible, favoring selfing. Most homostyles have both stigma and anthers at the mouth of the corolla tube (i.e., long-homostyly); short homostyly is rare (not shown). Long-homostyles stem from S-morphs and retain their compatibility type, thus can fertilize only L-morphs. Conversely, S-morphs cannot fertilize long homostyles due to stigma clogging in the latter. Red arrows indicate compatible, likely pollinations between floral morphs. Anthers are represented in yellow and stigmas in green.