When did the mistletoe family Loranthaceae become extinct in Tasmania? Review and conjecture

‘Mistletoe’ is the common name for a diverse group of hemi-parasitic shrublets that grow attached to and within the branches of trees and shrubs. Vidal-Russell and Nickrent (2008a) and Nickrent et al. (2010) infer that the mistletoe habit has evolved five times in the sandalwood order Santalales. The first of these clades is the family Misodendraceae, which is endemic to southern South America and whose species grow mainly on Nothofagus. The habit evolved three times within the Santalaceae – in the cosmopolitan tribe Visceae, which includes the ‘archetypal’ European Mistletoe Viscum album, in tropical American species of Santaleae that were formerly placed into a separate family, the Eremolepidaceae, and in the tropical tribe Amphorogyneae. The third clade comprises all members of the Loranthaceae except the early diverging genera Nuytsia and Atkinsonia. The family is restricted to the Southern Hemisphere except for a few genera growing north of the equator in the tropics and around the Mediterranean.

Two mistletoe clades are extant in Australia. These are (1) Visceae (three genera including Viscum), which is restricted to rainforests, monsoon forests and woodlands along the northern and eastern margins, and (2) Loranthaceae (12 genera), which is widely distributed across mainland Australia, with hosts ranging from coastal mangrove forests to mulga (Acacia aneura) woodlands in the arid zone (www.anbg.gov.au/abrs/online-resources/flora/redirect.jsp). Two Australian species are root parasites and for this reason give the appearance of being stand-alone shrubs or small trees – Nuytsia floribunda, which is endemic to southwest Western Australia, and Atkinsonia ligustrina, which is confined to exposed habitats in the Blue Mountains of NSW (Barlow 1984).

No mistletoes now occur in Tasmania. The reason(s) for this remain obscure given the wide ecological tolerance of many genera within the Loranthaceae and their observed dispersal over long distances by birds (www.anbg.gov.au/mistletoe/remote-islands.html). In this review, we illustrate and discuss the implications of Loranthaceae-type pollen recovered from a range of offshore and onshore sites around Tasmania (Figure 1). Unlike many fossil angiosperm pollen types, the morphology of these specimens is sufficiently distinctive to allow them to be assigned to this family and one of the six fossil species possibly to an extant genus.