Abstract
BackgroundWe revisit the palaeopalynological record of Loranthaceae, using pollen ornamentation to discriminate lineages and to test molecular dating estimates for the diversification of major lineages.MethodsFossil Loranthaceae pollen from the Eocene and Oligocene are analysed and documented using scanning-electron microscopy. These fossils were associated with molecular-defined clades and used as minimum age constraints for Bayesian node dating using different topological scenarios.ResultsThe fossil Loranthaceae pollen document the presence of at least one extant root-parasitic lineage (Nuytsieae) and two currently aerial parasitic lineages (Psittacanthinae and Loranthinae) by the end of the Eocene in the Northern Hemisphere. Phases of increased lineage diversification (late Eocene, middle Miocene) coincide with global warm phases.DiscussionWith the generation of molecular data becoming easier and less expensive every day, neontological research should re-focus on conserved morphologies that can be traced through the fossil record. The pollen, representing the male gametophytic generation of plants and often a taxonomic indicator, can be such a tracer. Analogously, palaeontological research should put more effort into diagnosing Cenozoic fossils with the aim of including them into modern systematic frameworks.
Highlights
The Loranthaceae, a moderately large family comprising about 76 genera and over 1,000 species in five tribes (Nickrent, 1997 onwards; Nickrent et al, 2010), has a wide geographical distribution
We investigated the fossil Loranthaceae pollen grains using the ‘single grain method’ (Zetter, 1989), whereby the same fossil pollen grain is first analysed under the light microscopy (LM) and scanning-electron microscopy (SEM)
The Eocene and Oligocene pollen grains documented in this study show morphologies (1) not found in any modern taxon studied so far (Stolzenbach MT, Profen MT1, Theiss MT), or (2) found exclusively in a single modern genus, or (3) are limited to a modern lineage (Elytrantheae: Profen MT3–5; core Lorantheae: Changchang MT) with none of the other modern species studied so far having an identical pollen
Summary
The Loranthaceae (order Santalales), a moderately large family comprising about 76 genera and over 1,000 species in five tribes (Nickrent, 1997 onwards; Nickrent et al, 2010), has a wide geographical distribution. Molecular studies on Loranthaceae (and Santalales in general) have focused on three issues: (1) clarifying the evolutionary relationships within the family (Vidal-Russell & Nickrent, 2008a); (2) explaining the transition from root to aerial parasitism (Wilson & Calvin, 2006); (3) dating the time of transition to aerial parasitism (Vidal-Russell & Nickrent, 2008b). The crown age of the aerial parasitic clade within the Loranthaceae, comprising the mostly New World Psittacantheae and Old World-Australasian Erytrantheae and Lorantheae, was placed in the middle Oligocene, approximately 28 Ma (estimated via a Bayesian relaxed clock and fixing the Santalales root to a maximum age of 114 Ma); a time characterised by global cooling (Zachos et al, 2001) and retreat of subtropical and tropical vegetation. Palaeontological research should put more effort into diagnosing Cenozoic fossils with the aim of including them into modern systematic frameworks
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