In article , Martin Cragg-
Barber writes
The form Corylus avellana contorta has female flowers that open before
the male in all specimens I have examined. Whether this relates to the
contorta mutation I wonder but apparently American researchers have
produced contorta forms from seed and it would be good to know if they
have this same character.
I have always assumed that the pollen release was simply because there
is much more pollen produced and so it makes sense to spread out the
time of release i.e. it's cheaper to produce redundant pollen than
redundant female flowers.

There's a phenomenon known as heterodichogamy in which some plants
produce pollen first and others produce mature stigmas first (I think it
applies to monoecious as well as hermaphrodite plants), which would seem
to be an adaptation for the promotion of outcrossing.

Apart from your comments above, I've no reason to believe that C.
avellana is heterodichogamous.
--
Stewart Robert Hinsley