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Whilst hybridism
has been constantly reported in Eucalyptus no hybrids between
species of different subgenera have ever been seen in the field.
Moreover, manipulated hybrids between species from different subgenera
have never been successful.
Hybridism requires genetic compatibility and synchronous flowering
times (unless manipulated). Hybrids between species within a subgenus
are rare in natural forests or scrubs. They are more likely to be
seen as regrowth trees or mallees in disturbed areas where changed
environmental conditions may be more amenable to the success of
the hybrid combination. Hybrids in stands appear to be selected
against in favour of the parent species.
Many reported hybrids are better interpreted as natural intergrades
between closely related species. e.g. E. burgessiana and
E. stricta in eastern New South Wales, E. dalrympleana
subsp. dalrympleana and E. viminalis subsp.
viminalis in Tasmania, and E. angulosa and E. incrassata
in coastal South Australia and Western Australia.
There are a few well-known formally named hybrids where both parents
have been identified and are seen in the field, e.g.
E. brachyphylla (E. kruseana
X E. loxophleba subsp.
lissophloia)
E. erythrandra (E. incrassata or E. angulosa
X E. tetraptera),
E. missilis (E. cornuta X E.
angulosa)
and possibly E. balanites (E. lanepoolei X E.
decipiens).
In another example, E. annuliformis,
only one
parent is evident, E. drummondii, the other being a mystery.
Many presumed hybrids have been formally named by botanists of the
eucalypts over the last 200 years. The most recent annotated list
of many of these names can be found in Chippendale (1988, pp. 428–442).
References
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