Fossil evidence from South America for the diversification of Cunoniaceae by the earliest Palaeocene

Abstract

Background and Aims Cunoniaceae are woody plants with a distribution that suggests a complex history of Gondwanan vicariance, long-distance dispersal, diversification, and extinction. Only four out of c. 27 genera in Cunoniaceae are native to South America today, but the discovery of extinct species from Argentine Patagonia is providing new information about the history of this family in South America Methods We describe fossil flowers collected from early Danian (early Palaeocene, ~64 Mya) deposits of the Salamanca Formation. We compare them with similar flowers from extant and extinct species using published literature and herbarium specimens. We used simultaneous analysis of morphology and available chloroplast DNA sequences (trnL–F, rbcL, matK, trnH–psbA) to determine the probable relationship of these fossils to living Cunoniaceae and the co-occurring fossil species Lacinipetalum spectabilum Key results Cunoniantha bicarpellata gen. et sp. nov. is the second species of Cunoniaceae to be recognized among the flowers preserved in the Salamanca Formation. Cunoniantha flowers are pentamerous, complete, the anthers contain in-situ pollen, and the gynoecium is bicarpellate and syncarpous with two free styles. Phylogenetic analysis indicates that Cunoniantha belongs to crown-group Cunoniaceae among the core-Cunoniaceae clade; although it does not have obvious affinity with any tribe. Lacinipetalum spectabilum, also from the Salamanca Formation, belongs to the Cunoniaceae crown-group as well, but close to tribe Schizomerieae Conclusions Our findings highlight the importance of west Gondwana in the evolution of Cunoniaceae during the early Palaeogene. The co-occurrence of Cunoniantha bicarpellata and Lacinipetalum spectabilum, belonging to different clades within Cunoniaceae, indicates that the diversification of crown-group Cunoniaceae was underway by 64 million years ago

Phylogenomics and biogeography of Cunoniaceae (Oxalidales) with complete generic sampling and taxonomic realignments

“…Secondly, the Southern Cone of South America appears to have been another significant center of diversity for the Cunoniaceae, with fossils described from the Paleocene and Eocene of Argentina. These comprise two extinct genera, Lacinipetalum Jud, Gandolfo, Iglesias & Wilf (Jud et al, 2018 ) and Cunoniantha Jud & Gandolfo (Jud and Gandolfo, 2021 ), as well as an extinct species of Ceratopetalum (Gandolfo and Hermsen, 2017 ), a genus now composed of nine extant species in Australia and New Guinea. In addition, fossils from the Oligocene of Tasmania have been placed in the genera Acsmithia Hoogland (= Spiraeanthemum ), Callicoma , Schizomeria , and Vesselowskya , although these genera no longer occur on this island (Carpenter and Buchanan, 1993 ), and a fossil assigned to Codia was described from the middle Eocene to Oligocene of Western Australia (Barnes and Hill, 1999 ), although this genus is now confined to New Caledonia.…”

Cunoniaceae infructescences from the early Eocene Laguna del Hunco flora, Patagonia, Argentina

“…or Cunonieae more broadly. It should be noted, however, that Jud and Gandolfo (2021) expressed reservations about the assignment of Cretaceous and Paleogene Weinmannioxylon wood to crown Cunoniaceae; furthermore, not all species of Weinmannioxylon are thought to be related to Weinmannia s.l. or other genera of Cunonieae (discussed further below).…”

“…Weinmannioxylon multiperforatum (the type species) and Weinmannioxylon pluriradiatum , also considered similar to wood of Weinmannia s.l. and Cunonia (Petriella, 1972; Brea et al, 2015), have been found at several Paleogene localities in Chubut and Neuquén provinces in Argentina (Petriella, 1972; Raigemborn et al, 2009; Brea et al, 2015; Jud and Gandolfo, 2021). One Neogene occurrence of wood from the Falkland (Malvinas) Islands has been assigned to cf.…”

“…have been found at several Paleogene localities in Chubut and Neuquén provinces in Argentina (Petriella, 1972;Raigemborn et al, 2009;Brea et al, 2015;Jud and Gandolfo, 2021). One Neogene occurrence of wood from the Falkland (Malvinas) Islands has been assigned to cf.…”

“…The macrofossil record of Patagonia indicates the existence of multiple lineages of Cunoniaceae by the Paleogene; it was recently summarized by Jud and Gandolfo (2021) and is briefly updated here. The earliest Cunoniaceae macrofossil records from the southern hemisphere are Late Cretaceous wood assigned to the genera Eucryphiaceoxylon and Weinmannioxylon from Antarctica (Pujana et al, 2018;Poole et al, 2000;Jud and Gandolfo, 2021; Figure 1) whereas the Patagonian record begins in the early Paleocene (early Danian) (Jud et al, 2018;Iglesias et al 2021;Jud and Gandolfo, 2021). Most Paleocene to Eocene macrofossil reports of Cunoniaceae from Patagonia are from Chubut Province, Argentina.…”