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ISHS Acta Horticulturae 615: IV International Conifer Conference

THE WOLLEMI PINE, ANOTHER LIVING FOSSIL?

Author:   K.D. Hill
Keywords:   Araucariaceae, Araucarioides, branching pattern, cuticle micromorphology, Dilwynites, epicuticular wax, leaf morphology, orthotropy, plagiotropy, pollen, Wollemia
DOI:   10.17660/ActaHortic.2003.615.13
Abstract:
The discovery of the Wollemi Pine (Wollemia nobilis) in late 1994 excited international interest. These tall trees represent a genus in the conifer family Araucariaceae with close fossil links dating back to the Mesozoic era, but previously unknown as living organisms. Three very small stands numbering less than 50 adult individuals occur, in a narrow canyon in the sandstone massif of the Wollemi Wilderness, within 150 km of Sydney. The Wollemi Pine grows as a slender emergent above the canopy of warm temperate rainforest dominated by Ceratopetalum apetalum and Doryphora sassafras. Although clearly a member of the Araucariaceae, the Wollemi Pine possesses unique features such as the spongy nodular bark, the cones borne terminally on first-order branches, and the epicormic branching habit. Adult and juvenile leaves are highly dimorphic, as are leaves on plagiotropic and orthotropic shoots. All leaves show thick cuticle and smooth epidermal cell surfaces, with stomata randomly orientated, sunken and lacking any Florin ring development. Juvenile plagiotropic shoots have chartaceous, hypostomatic leaves, whereas those of adult plagiotropic shoots are coriaceous and amphistomatic. Juvenile leaves display a very compact amorphous wax on the upper surface and a thick, finely granular wax on the lower surface, including over the stomatal plugs. Adult leaves have compact amorphous wax on both surfaces, with massive stomatal plugs. Cuticular morphology is most like that of Araucaria section Eutacta of all extant groups, but is even more similar to that of the fossil genus Araucarioides. However, leaf morphology suggests that Wollemia and Araucarioides may be generically distinct. Features shared with Araucaria include broad-based leaves with no abscission zone, terminal seed and pollen cones, spinescent bract-scales, and lack of Florin rings. Features shared with Agathis include wholly fused bract-scales, winged seeds that are shed free from the bract-scales, and obtuse leaves. Close links exist with both pollen and macrofossils from the late Cretaceous and early Tertiary, most likely from genera closer to Wollemia than either Agathis or Araucaria. DNA sequence data indicate that Wollemia is closest to Agathis, both Agathis and Araucaria are monophyletic, and Podocarpaceae are the sister group to Araucariaceae

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