>----------
>From: Andrew Taylor[SMTP:
>Sent: Monday, 5 May 1997 1:48 PM
>
>To expand on Philip Maher's comments. I believe there are about 60
>Australian members of the family Loranthacae which are aerial stem
>parasites and are hence likely to get the common name Mistletoe.
The members of the family Viscaceae are known as mistletoes too.
>
>These 60 species seem to vary greatly in host specificity. Some are found
>on a wide variety of host species, some are found usually on hosts from a
>particular genus or family and a few mistletoe species occur almost always
>on a single host species.
As Phil pointed out, some mistletoes primarily parasitise other
mistletoes (eg. Dendropthoe on Amyema; Am. miraculosum on other Amyema),
& it's hard to envisage the adaptive significance of leaf shape there!
Common Brushtail Possums are quite keen on chomping mistletoe leaves,
but I don't imagine leaf shape offers much protection in that case, as
the mistletoe plants are essentially arboreal shrubs and their profile
in a tree stands out like a sore thumb (are possums any good at spotting
sore thumbs?). Mistletoe foliage usually smells different to the host's
too, and I imagine possums can detect this quite readily.
Whilst some species are quite host specific, this tends to vary from
location to location for some species, suggesting to me some kind of
environmental determinant of parasite germination success (such as other
stresses on potential host trees). For example where I live, Drooping
Mistletoe (Amyema pendulum) in contiguous forest is primarily found on
Eucaltypus (stringybarks, ashes, peppermints & gums in the main). There
are however a couple of particular roadside locations where it is also
rampant on wattles (Blackwood, Golden Wattle, Silver Wattle, Late Black
Wattle). Normal wattle mistletoes, Wire-leaf (Am. preissii) and Grey
(Am. quandang), are also common at these locations. Isolated,
one-tree-wide strips are often under stress from soil degradation, fire,
wind, altered hydrology, pollution, etc., perhaps bringing about a
subtle alteration to host biochemistry & making some normally resistant
or unsuitable trees vulnerable.
Although some of the Amyema mistletoes have quite a tendency to be host
specific (at least to genus, if not species), other genera such as
Loranthus are more flexible. In my experience in Western Victoria,
Harlequin Mistletoe (Loranthus exocarpi) is found (at least) on
Heterodendrum, Bursaria, Acacia, Myoporum, and Allocasuarina (6 species,
5 families), whereas Buloke Mistletoe (Am. linophyllum) is only found
on Buloke (Allocasuarina luehmanii). Harlequin Mistletoe leaves look
like none of the hosts, but Buloke Mistletoe looks just like Buloke.
Painted Honeyeaters (old endemics) have ONLY been seen to utilise a
handful of Amyema mistletoes (had to get them in here somewhere);
Mistletoebirds (johnny-come-lately) use most or all mistletoes. Many
Australian blue (Lycaenidae) and white (Pieridae) butterflies have
host-specific relationships with particular mistletoe species. It may
be that Amyema has been in Oz longer than the rest, setting up these
specialised, co-evolved relationships with Oz plants and animals.
Creeping Mistletoe (Muellerina eucalyptoides) parasitises a wide range
of exotic Northern Hemisphere trees in suburbia (Prunus spp, apple,
Quercus spp., liquidamber, birch, etc.), suggesting perhaps a
relationship with related plants earlier in time when continents were
otherwise arranged?? or is it just rapaciously filling a vacant niche??
In exotic gardens the vectors must be honeyeaters or rosellas or
whatever, because there's often no Mistletoebirds in these areas. It's
otherwise widely found on River Red Gum (E. camaldulensis) around
Geelong.
>
>I'm certainly not an expert on any of the above.
Neither am I, but aren't they good value!? Putting it back in a birding
context; visit a big flowering Box Mistletoe (Am. miquelii) clump in
winter & enjoy the hordes of nectarivorous birds making use of it.
>
Lawrie Conole
>Geelong, Victoria, Australia
>
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