Mistletoes - biogeography
Loranth history in Australia
How does mistletoe biogeography in Australia contribute to our understanding of the evolution of the Australian flora as a whole?
The northward separation of Australia from Antarctica commenced about 125 million years ago (Ma), but movement remained slow (4.5 mm/yr) until 55 Ma, when it increased to 60-70 mm/yr. Narrow land connections between Australia, Antarctica and South America may have persisted until 40 Ma, and when circumpolar oceanic circulation was initiated, heat transport from equator to pole was reduced, temperature gradients increased, and arid conditions started to overtake Australia from the south. Our unique scleromorphic flora developed in response to these changes. Thus we can identify a Gondwanan element in the Australian flora, derived from the original plant stocks which were there at the time of separation. Within it we can identify two subelements: a relict sub-element representing the little-changed descendents of the original Gondwanan flora (found mainly in our rain forests), and the derived autochthonous sub-element represented by our arid-adapted scleromorphic flora.
The northward-moving Australian plate collided with the volcanic arcs of the Sunda region in the Miocene, and by 7 Ma a connection to Asia and a land plant migration route was established. The strong floristic contact led to an exchange of plants in both directions. We can therefore identify a second element in the Australian flora, the intrusive element, comprising the descendents of plant groups which reached Australia/New Guinea subsequent to its isolation from Gondwanaland, and much of this element has been derived from our tropical northwest.
We can place Australian/New Guinean Loranthaceae in both elements of the Australian flora (see Table). Accordingly we can create a scenario for the history of loranths in the Australian region.