The term may sound unfamiliar but it is something that lots of plants exhibit and is it a way that plants use to prevent self pollination and a small gene pool, as unwanted in the plant world as it is in humans and other breeding systems. (except for those apomictic plants mentioned the other day, of course)

Most flowers have both male and female parts so it would be easy for the pollen of a flower to land on its stigma and effectively pollinate itself. Plants have various ways to prevent this and the two parts may be far apart or, as in dichogamous plants, the two parts ‘ripen’ at different times. So some plants open their stigmas first, before the stamens shed pollen and others shed pollen first and when it is gone the stigmas then become receptive. A plant that is functionally male first is called protandrous and one that is female first is protogynous (sensible really since proto means first). If the style, on which the stigma is located, is longer than the stamens it can help prevent stray pollen landing on it.

Foxgloves are protandrous and the stamens start to open as soon as the flower expands. Afterwards they are then functionally female. This means that the lower flowers on a spike are female and the upper ones are male. Since bumble bees always fly to the base of the spike and work their way up it ensures that pollen from one flower is deposited on the flowers of a different plant.

dichogamy, foxglove pollination, protandrous, protogyny