The history of Ilex (Aquifoliaceae) with special reference to Australia: Evidence from pollen

Abstract

Ilex is cosmopolitan excluding the arid and arctic areas and consists of some 400 species. Australia has one species, Ilex arnhemensis, which is restricted to the north.

The pollen of Ilex is very distinctive and fossil specimens can be related to it with certainty. There is an undescribed fossil species in the Turonian (earliest Upper Cretaceous) of south-eastern Australia, where Ilex predates the first appearance of Nothofagus. Ilexpollenites spp. are usually present from Maastrichtian (latest Upper Cretaceous) to late Miocene. Elsewhere in the world there are three other Cretaceous records and abundant Tertiary occurrences from every geographic region. Ilex was cosmopolitan throughout the Tertiary and it may have been world wide in the Upper Cretaceous also.

Ilex grows as a tree or shrub and requires a relatively wet and equable climate (with perhaps a few exceptions). The seeds are dispersed by birds and the embryo undergoes continuous development until germination which may take from 2 to 8 years. Such strategies must be an asset for a wide distribution.

Previous works on modern distributions and morphology have implicated south-eastern Asia as the place of origin of Ilex. The fossil record does not support this hypothesis although it is not sufficient to pinpoint its origin. At the time when Ilex evolved, more equable climates extended much further towards the poles than they do today. The south-east Asian region has had one of the most stable climates and is a refuge for ancient angiosperms, regardless of place of origin. No doubt the development of aridity in Australia has restricted Ilex to the north.