Saturday, July 24, 2010

Needle-leaf Mistletoe

Amyema cambagei

Here’s a plant that hides itself well!

I would have walked right past it on this tree, if my attention hadn’t been drawn by the much more conspicuous “variable mistletoe” Amyema congener. (Notice its leaves in the photo at left.)

Yet like many “edge trees” this belah Casuarina cristata at Irongate is carrying a large community of mistletoes.
Most of them are the well-camouflaged needle-leaf mistletoe, and once I had noticed it, I realised that it was flowering prettily.
It’s a curious thing that some mistletoes have evolved to mimic their most usual hosts. At first glance this seems self-defeating. Surely a plant wants to be conspicuous to the birds which eat its fruits, and therefore distribute its seeds? However, there is a theory to explain it.
To begin with, mistletoes want to hide from predators. Possums find their foliage much tastier than that of many mistletoe host plants, and appreciate its higher water content. (In New Zealand, which was possum-free before human interference introduced the pesky beasts, mistletoes which are closely related to the Australia ones haven’t developed the ability to mimic their hosts. Possums have now driven at lest one New Zealand mistletoe to extinction.)
There are some butterflies - jezebels and azures - which lay their eggs on no plants except mistletoes, so depend on them for survival. Perhaps the mistletoes are trying to avoid some caterpillar-grazing as well, though it seems unlikely as butterflies are more likely to find their hosts by their smell.
Meanwhile, it is possible that birds know to look for the host plants, and only when they have found them do they begin to search for mistletoe fruits. This would explain why mistletoes tend to get spread among the same species of host plant even when they can survive on others.
As you might expect, this plant is usually found on she-oaks, though it does sometimes find its way onto Eucalyptus and Eremophila hosts, exploding the myth that mistletoes are unable to thrive on anything other than their most usual hosts.
Needle-leaf mistletoes are pretty plants. The whole plant is covered with pale grey down, and the plum-red flowers, with their bright yellow stamens, emerge from pale velvety buds, retaining this texture on the outer base of the flower. The little fruits are pinkish red.

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