Friday, 31 May 2013

On mistletoe

The (sort of) traditional view:
On Googling 'mistletoe' I came up with a bunch of links to an alleged song by someone called Justin Bieber who I believe aims his work at the wannabe Princess market.  I have never heard him warble so I shouldn't criticise.

Adding the word 'cartoon' to the search came up with some more helpful works, although many of them were obviously done by people with better skills in art and humour than botany.  Even at very low resolution I can tell that is Holly (Ilex aquifolium) - the red berries are a big hint - rather than the common mistletoe (Viscum_album)  with white berries, employed to encourage a little of this and that and, if you are very lucky, the other, around Christmas.

There is nothing like starting a post with a screen full of irrelevance!  Taking text from Wikipedia "Mistletoe is the common name for obligate hemi-parasitic plants in several families in the order Santalales. These plants attach to and penetrate the branches of a tree or shrub by a structure called the haustorium, through which they absorb water and nutrients from the host plant."

The reason I am writing about this set of plants is the debate on the last ANPS WW about two members of Australian mistletoes, genus Amyema common in the Canberra region.  My post from that walk includes an image of A. miquelii:
Notice that all three of the residual flowers have stalks (aka pedicels).  

We also found on the walk, a flower head of A. pendula but I didn't at the time photograph it.  That omission has been remedied at home:
The fact of flowering at this time of year is a big hint towards A. pendula, but the definitive attribute is the lack of a pedicel on the central floret.
In other words, the species whose name suggests hanging down, does so less than the other common species. (I will note in passing that the species used to be called Amyema pendulum but APNI now reduces that to a mere "orthographic variant"!  I have tried to find the reasons for this change but other than finding it came from the Australian Plant Census have been unsuccesful: perhaps it was just lining up the sex of the words?)

In the local region we have - as far as I am aware - 4 species of mistletoe, in the family Loranthaceae.  A third species in the genus Amyema, A. cambagei is a parasite of Allocauarinas and mimics them rather well making it very difficult to spot them (I haven't found it in any of the visits I have entered so far).  The 4th species Muellerina eucalyptoides - is again a parasite of eucalypts  - and on my observations is far less common that the Amyemas.  A fifth species A. congener is found on the limit of our range to the NE (ie Bungonia) which is also about the western extreme of its range: it also parasitises Allocasurinas.

The distribution of the 4 species, recorded in 32 of 130 Wednesday Walks I have entered to a database, is illustrated in this snip from Google Earth. ( I am very surprised at the absence of records from the Brindabellas/Namadgi.  My friend Ros has suggested this is because the trees are too high - probably a fair call, for differentiating miquelii from pendula.)
Yellow is A. miquelii, turquoise is A. pendula/pendulum; big red drop is A. congener;  big green drop is Muellerina eucalytpoides.

A final thought is to note that mistletoe is seen as a keystone resource (ie leads to a high level of environmental richness) . The seminal work (sorry about that word - it is in fact a polite, even if chiched,  one) is by Watson and Herring.  Incidentally, full praise to them for the full text being available at no cost rather than the rip-off rates usually charged by academia.

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