Leaf preservation in Eucalyptus woodland as a model for sclerophyll fossil floras

Abstract

Retallack, G.J., 7 May 2018. Leaf preservation in Eucalyptus woodland as a model for sclerophyll fossil floras. Alcheringa 43, 71–84.

A comparison of 29 identifiable vascular plant species in litter beneath Eucalyptus woodland with at least 74 species living nearby showed that the litter is a poor representation of standing vegetation. The leaf litter is dominated by sclerophyll leaves, which are a factor of 6.2 over-represented in litter for Angophora costata, factor of 5.7 for Melaleuca linariifolia, of 3.6 for Eucalyptus spp., of 3.5 for Pteridium esculentum and of 2.1 for Acacia linifolia. Angophora leaves are favored by lignification, with denser venation than Eucalyptus leaves. Sparse emergent oil glands of Angophora also provide fewer entry points for bacteria than rotted internal oil glands of Eucalyptus. The myrtaceous taxa Angophora, Eucalyptus, Melaleuca and Kunzea all have oils dominantly of preservative terpene. Melaleuca linariifolia and Acacia linifolia also have leaves and phyllodes (respectively) that are narrow with a thick lignin midrib. Thickly cuticled, succulent, hirsute, pubescent, and pinnate leaves, and green stems are not favored for preservation, because they rot from the inside out. Conspicuously absent in the leaf litter are nonsclerophyll leaves, most grasses and low herbs. This modern sclerophyll leaf litter matches Sydney Basin Permian and Triassic fossil plant localities above nutrient-poor siliceous paleosols, which may have had much more diversity than the preserved fossil flora. Clayey calcareous paleosol leaf litters and lake deposits may record a truer record of local floristic diversity in deep time than sclerophyll leaf litters.

Gregory J. Retallack [[email protected]], Department of Earth Sciences, University of Oregon, Eugene, OR 97403-1272, USA.

Key words:

• Taphonomy
• leaf litter
• Angophora
• Dicroidium
• Lepidopteris

Acknowledgments

I thank Frank J. Burrows for inspiration to conduct this study, and access to scales and other equipment. Heather Adamson, Alison Edgecombe, Jean Vanry and N.C.W. Beadle helped with plant identification. Bob Spicer offered useful comments on an earlier draft.