Charlie Pridham writes

Violets often produce seed without needing fertilization,

Not only that, but without producing the full-scale showy flower. Do
they produce an insignificant flower which self fertilises, or what?

while other plants
seem to know if the plant is related and will not set seed readily by
crossing either with other flowers on themselves

Others will set seed with their own pollen, but have mechanical ways of
avoiding it - for example, it may have different sexed flowers appearing
at different times (eg courgette) or the stigma and anthers may grow at
different rates - stigma may be prominent at first to get good chance of
cross pollination, but if that fails, it will bend towards anthers and
pick up its own pollen (eg hippeastrum)

or a clone of themselves
but will set seed quite happily with a different genetic clone (i.e.
Lapageria) The plants I have the most trouble getting to set fruit are
Holboellia's and Akebia's, nothing I have tried seems to work, answers on a
postcard please!


--
Kay