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How does protandry promote cross-pollination in fireweed and salvias?

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A honeybee collects pollen from the yellow stamens of a pink and cream honeysuckle flower against a blurred green background. — Pollination Common carder bumblebee (*Bombus pascuorum*) pollinating a honeysuckle (*Lonicera* species) flower.

In plants such as fireweed (Epilobium angustifolium) and salvias (Salvia species), protandry serves as a temporal mechanism to prevent self-fertilization and promote cross-pollination.12

Protandry is a form of dichogamy in which the stamens (the male reproductive organs) ripen and shed pollen before the pistils (the female reproductive organs) on the same flower or plant become receptive. By ensuring that the male and female functions are temporally separated, the plant reduces the likelihood that its own pollen will fertilize its own ovules.123

This timing mismatch encourages pollinators to carry pollen from a plant in the male phase to a different plant that is currently in the female phase, thereby facilitating outbreeding and increasing genetic variability within the population.2