Variation in within‐morph incompatibility inhibition sites in heteromorphic Primula L.

SUMMARY The inhibition sites for within‐morph incompatibility are reported for 52 species of Primula. Pollen tube inhibition usually occurs at more than one site; when only one site is involved, this is at the stigma surface. Inhibition sites usually vary between pins and thrums within a species, and inhibition characteristics vary widely between species, although related species are frequently similar. There is a close relationship between illegitimate seed set and failure of illegitimate tube inhibition. Total within‐morph incompatibility is only observed in two species, but for almost all species some compatibility is found in both morphs. Inhibition at the stigma surface results in more efficient incompatibility than inhibition within the stigma and style, although multiple‐site inhibition is the most efficient. Within‐thrum inhibition tends to occur more frequently at the stigma surface than does within‐pin inhibition. Four main classes of inhibition characteristics are noted. Some sections show inhibition site complexity in pins, but in others it has developed in thrums. Species with complex within‐morph inhibition in both pins and thrums occur in several unrelated taxonomic groupings.