Abstract
BackgroundThe aquatic flowering-plant family Hydatellaceae has a classic Gondwanan distribution, as it is found in Australia, India and New Zealand. To shed light on the biogeographic history of this apparently ancient branch of angiosperm phylogeny, we dated the family in the context of other seed-plant divergences, and evaluated its biogeography using parsimony and likelihood methods. We also explicitly tested the effect of different extinction rates on biogeographic inferences.ResultsWe infer that the stem lineage of Hydatellaceae originated in the Lower Cretaceous; in contrast, its crown originated much more recently, in the early Miocene, with the bulk of its diversification after the onset of the Pliocene. Biogeographic reconstructions predict a mix of dispersal and vicariance events, but considerations of geological history preclude most vicariance events, besides a split at the root of the family between southern and northern clades. High extinction rates are plausible in the family, and when these are taken into account there is greater uncertainty in biogeographic inferences.ConclusionsA stem origin for Hydatellaceae in the Lower Cretaceous is consistent with the initial appearance of fossils attributed to its sister clade, the water lilies. In contrast, the crown clade is young, indicating that vicariant explanations for species outside Australia are improbable. Although long-distance dispersal is likely the primary driver of biogeographic distribution in Hydatellaceae, we infer that the recent drying out of central Australia divided the family into tropical vs. subtropical/temperate clades around the beginning of the Miocene.
Highlights
The aquatic flowering-plant family Hydatellaceae has a classic Gondwanan distribution, as it is found in Australia, India and New Zealand
Simulation studies show that area extinction rates in Lagrange are strongly biased towards zero [67]; as an alternative we evaluated lineage extinction rates [70] as a proxy for the area extinction rate, the parameter used in our analyses
Molecular dating and diversification Hydatellaceae are estimated to have diverged from the water lilies 126.7 Millions of (Ma) (120.6–133.2 Ma, 95% Highest posterior density (HPD)), in the Lower Cretaceous, with a crown clade age of 19.1 Ma (15.7–23.4 Ma, 95% HPD), in the early Miocene
Summary
The aquatic flowering-plant family Hydatellaceae has a classic Gondwanan distribution, as it is found in Australia, India and New Zealand. Hydatellaceae were recently recognized as the sister group of the water lilies (Cabombaceae and Nymphaeaceae), placing their divergence close to the root of angiosperm phylogeny e.g., [10]. They have since attracted considerable attention because of the insights they may provide into the evolution of early angiosperms [11,12,13,14,15,16]. Of particular interest is the nature of the reproductive structures in the family, which may represent floral, prefloral, or pseudanthial arrangements of reproductive organs, and the incidence of unisexual and bisexual reproductive units These may bear on our understanding of the ancestral floral Bauplan of angiosperms [8,9,13]. Contemporary taxonomic and phylogenetic work on the family recognizes one genus, Trithuria Hook. f., and 12 species in four monophyletic sections [8,9]
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