June: NS Branch Meeting Report
Although our speaker Dr Tony Start was introduced to mistletoes as a child in Kenya, it was his move to the Pilbara in WA as regional superintendent of national parks that rekindled his interest. Knowing the area was prone to wildfires and that mistletoes don’t survive fires, he set about surveying and collecting the mistletoes in the Kimberley, Pilbara and Gascoyne to see if they could be used as surrogate indicators of long-unburnt country. This research then extended to the whole of the state and ultimately led to improved distribution maps of the many species which occur here, including several endemic species.
Botanically, mistletoes are hemi-parasitic stem parasites, which in WA belong to either the Santalaceae or Loranthaceae families. Elsewhere, the former includes the classic mistletoes of Europe (the ones you kiss under) while the latter contains what are sometimes referred to as the “showy” mistletoes.
The two mistletoes in the Santalaceae family that occur in southern WA are both under threat. Korthalsella arthroclada is very sensitive to hydrology changes while K. leucothrix, which lives on acacia species, is endangered because the seedlings of the hosts are being eaten by rabbits. Tony has not been able to find any specimens at a previous site near the border with South Australia.
The Loranths of southern WA are more numerous and colourful. Most have red flowers and red berries: probably an evolutionary trait to attract birds. Lysiana casuarinae , which as the name implies grow on casuarinas including those along the Swan River, is identifiable by its thin banana-shaped yellow flowers (bright red in the Murchison and Gascoyne variety). Amyema linophylla is another species growing on casuarinas (but not Allocasuarinas) and also common along the upper reaches of the Swan River.
Tony then introduced us to the other six species of Amyema, most of which have a wide distribution.
- A. fitzgeraldii is common in the mulga and has edible fruit
- A. gibberula only grows on two species of Hakea, having matchstick flower stems
- A. melaleucae grows only on melaleucas, mainly M. lanceolata, and probably once occurred from Shark Bay to South Australia but is now only in isolated pockets including Garden Island (but extinct on Rottnest)
- A. miquelii is probably the one most familiar to people as it grows on eucalypts and sometimes bottlebrushes
- A. miraculosa is unusual in that it grows on other parasitic plants such as quandongs and sandalwoods, and along the coast on Myoporum species, having yellow berries
- A. preissii is another species which prefers acacias, sometimes having yellow flowers instead of red
- A. nestor has a flower that’s very photogenic, grows mostly in acacias, beyond the Jarrah forests, particularly in the Wheatbelt.
Stem parasites rely on birds, particularly the Mistletoe Bird, to spread their sticky seeds (above, Joff Start), which means areas that are prone to fires—and which therefore have few mature trees—are less likely to be recolonised, particularly if the mistletoes are host specific. While no symbiotic relationship is known between mistletoes and their hosts, mistletoes are keystone species as they provide food for birds and butterflies, which in turn pollinate other plants which then disperse seeds whose mature plants contribute to nutrient recycling and provide the host for the next generation of mistletoes.