Two fossil species of Metrosideros (Myrtaceae) from the Oligo-Miocene Golden Fleece locality in Tasmania, Australia.

PREMISE OF THE STUDY: The capsular-fruited genus Metrosideros (Myrtaceae) is one of the most widely distributed flowering plant genera in the Pacific but is extinct in Australia today. The center of geographic origin for the genus and the reason for and timing of its extinction in Australia remain uncertain. We identify fossil Metrosideros fruits from the newly discovered Golden Fleece fossil flora in the Oligo-Miocene of Tasmania, Australia, shedding further light on these problems. METHODS: Standard paleopalynological techniques were used to date the fossil-bearing sediments. Scanning electron microscopy and an auto-montage camera system were used to take high-resolution images of fossil and extant fruits taken from herbarium specimens. Fossils are identified using a nearest-living-relative approach. KEY RESULTS: The fossil-bearing sediments are palynostratigraphically dated as being Proteacidites tuberculatus Zone Equivalent (ca. 33-16 Ma) in age and provide a confident Oligo-Miocene age for the macrofossils. Two new fossil species of Metrosideros are described and are here named Metrosideros dawsonii sp. nov. and Metrosideros wrightii sp. nov. CONCLUSIONS: These newly described fossil species of Metrosideros provide a second record of the genus in the Cenozoic of Australia, placing them in the late Early Oligocene to late Early Miocene. It is now apparent not only that Metrosideros was present in Australia, where the genus is now extinct, but that at least several Metrosideros species were present during the Cenozoic. These fossils further strengthen the case for an Australian origin of the genus.

Plant traits demonstrate that temperate and tropical giant eucalypt forests are ecologically convergent with rainforest not savanna.

Ecological theory differentiates rainforest and open vegetation in many regions as functionally divergent alternative stable states with transitional (ecotonal) vegetation between the two forming transient unstable states. This transitional vegetation is of considerable significance, not only as a test case for theories of vegetation dynamics, but also because this type of vegetation is of major economic importance, and is home to a suite of species of conservation significance, including the world's tallest flowering plants. We therefore created predictions of patterns in plant functional traits that would test the alternative stable states model of these systems. We measured functional traits of 128 trees and shrubs across tropical and temperate rainforest - open vegetation transitions in Australia, with giant eucalypt forests situated between these vegetation types. We analysed a set of functional traits: leaf carbon isotopes, leaf area, leaf mass per area, leaf slenderness, wood density, maximum height and bark thickness, using univariate and multivariate methods. For most traits, giant eucalypt forest was similar to rainforest, while rainforest, particularly tropical rainforest, was significantly different from the open vegetation. In multivariate analyses, tropical and temperate rainforest diverged functionally, and both segregated from open vegetation. Furthermore, the giant eucalypt forests overlapped in function with their respective rainforests. The two types of giant eucalypt forests also exhibited greater overall functional similarity to each other than to any of the open vegetation types. We conclude that tropical and temperate giant eucalypt forests are ecologically and functionally convergent. The lack of clear functional differentiation from rainforest suggests that giant eucalypt forests are unstable states within the basin of attraction of rainforest. Our results have important implications for giant eucalypt forest management.

Unified changes in cell size permit coordinated leaf evolution.

The processes by which the functions of interdependent tissues are coordinated as lineages diversify are poorly understood. Here, we examine evolutionary coordination of vascular, epidermal and cortical leaf tissues in the anatomically, ecologically and morphologically diverse woody plant family Proteaceae. We found that, across the phylogenetic range of Proteaceae, the sizes of guard, epidermal, palisade and xylem cells were positively correlated with each other but negatively associated with vein and stomatal densities. The link between venation and stomata resulted in a highly efficient match between potential maximum water loss (determined by stomatal conductance) and the leaf vascular system's capacity to replace that water. This important linkage is likely to be driven by stomatal size, because spatial limits in the packing of stomata onto the leaf surface apparently constrain the maximum size and density of stomata. We conclude that unified evolutionary changes in cell sizes of independent tissues, possibly mediated by changes in genome size, provide a means of substantially modifying leaf function while maintaining important functional links between leaf tissues. Our data also imply the presence of alternative evolutionary strategies involving cellular miniaturization during radiation into closed forest, and cell size increase in open habitats.