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Turner Review No. 2 Southern Conifers in Time and Space

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Hill, RS and Brodribb, TJ (1999) Turner Review No. 2 Southern Conifers in Time and Space. Australian Journal of Botany, 47 (5). pp. 639-696. ISSN 0067-1924

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Abstract

The three southern conifer families, Araucariaceae, Cupressaceae and Podocarpaceae, have a long
history and continue to be an important part of the vegetation today. The Araucariaceae have the most
extensive fossil record, occurring in both hemispheres, and with Araucaria in particular having an
ancient origin. In the Southern Hemisphere Araucaria and Agathis have substantial macrofossil records,
especially in Australasia, and Wollemia probably also has an important macrofossil record. At least one
extinct genus of Araucariaceae is present as a macrofossil during the Cenozoic. Cupressaceae
macrofossils are difficult to identify in older sediments, but the southern genera begin their record in the
Cretaceous (Athrotaxis) and become more diverse and extensive during the Cenozoic. Several extinct
genera of Cupressaceae also occur in Cretaceous and Cenozoic sediments in Australasia. The
Podocarpaceae probably begin their macrofossil record in the Triassic, although the early history is still
uncertain. Occasional Podocarpaceae macrofossils have been recorded in the Northern Hemisphere, but
they are essentially a southern family. The Cenozoic macrofossil record of the Podocarpaceae is
extensive, especially in south-eastern Australia, where the majority of the extant genera have been
recorded. Some extinct genera have also been reported from across high southern latitudes, confirming
an extremely diverse and widespread suite of Podocarpaceae during the Cenozoic in the region.
In the Southern Hemisphere today conifers achieve greatest abundance in wet forests. Those which
compete successfully with broad-leaved angiosperms in warmer forests produce broad, flat
photosynthetic shoots. In the Araucariaceae this is achieved by the planation of multiveined leaves into
large compound shoots. In the other two families leaves are now limited to a single vein (except
Nageia), and to overcome this limitation many genera have resorted to re-orientation of leaves and twodimensional
flattening of shoots. The Podocarpaceae show greatest development of this strategy with 11
of 19 genera producing shoots analogous to compound leaves. The concentration of conifers in wet
forest left them vulnerable to the climate change which occurred in the Cenozoic, and decreases in
diversity have occurred since the Paleogene in all regions where fossil records are available. Information
about the history of the dry forest conifers is extremely limited because of a lack of fossilisation in such
environments. The southern conifers, past and present, demonstrate an ability to compete effectively
with angiosperms in many habitats and should not be viewed as remnants which are ineffectual against
angiosperm competitors.

Item Type: Article
Journal or Publication Title: Australian Journal of Botany
Page Range: pp. 639-696
ISSN: 0067-1924
Date Deposited: 10 Dec 2007 00:47
Last Modified: 18 Nov 2014 03:25
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