In article , Kay Easton
writes
Heterostylous means that the species is polymorphic for style length.
It's associated with outcrossing, but I forget the details. Many
Primulas are heterostyles, and the trait turns up in other taxa as well.

In primroses, you get the pin and thrum flowers, depending on whether
the stigma is above or below the stamens (as a technique to encourage
cross-pollination). Is this what you mean?

Yes.
--
Stewart Robert Hinsley