Abstract Detail


Siegert, Caroline [1], Gandolfo, Alejandra [1], Wilf, Peter [2].

A new fossil Malvaceae fruit from the Early Eocene of Patagonia, Argentina.

A suite of fossil infructescences and isolated fruits, with characters strongly suggesting affinities to the family Malvaceae and subfamily Malvoideae, were collected from the early Eocene Laguna del Hunco site, Huitrera Formation, Chubut, Argentina. The site represents a caldera lake of approximately 52 Ma with a diverse flora representing a mesic rainforest. Many of the fossil plant species found at Laguna del Hunco and throughout Patagonia have biogeographic connections to Australia, Malesia, and northern South America. The new fossil infructescences are spikes to racemes that display alternate phyllotaxy among their branches as well as the fruits. They bear schizocarps born directly on the axis (“ramiflorous” fruits) or on short peduncles that are subtended by a bract; the schizocarps display an infracarpelar disk and split completely into five ovate mericarps. The mericarps are characterized by their acute apex and the presence of a ridge down their middle. Isolated schizocarps show the same features as the infructescences. The fossils were compared with several families that produce schizocarps on inflorescences, and based on the features observed in the fossils, it is clear that they are more similar to those of the cosmopolitan family Malvaceae. The fossils share characters with several modern Malvaceae genera, such as Julostylis, Plagianthus, Sida, and Sphaeralcea, all of which belong to the subfamily Malvoideae. Based on those comparisons, the fossils show a particular resemblance with species of extant Sida from the tribe Malveae but differ in several features that are widepread in the genus, suggesting the need for erecting a new genus. The family Malvaceae comprises ~4500 extant species within 250 genera distributed worldwide; the subfamily Malvoideae is found in the warm and temperate regions of all continents, but two-thirds of its genera are restricted to the Americas. The presence of Malvaceae at Laguna del Hunco was suggested in the 1920s by E.W. Berry, who gives a description of the fossil genus Malvacarpus, which represents fruits that are distinctly different than the ones in question, along with several Malvaceae leaves. However the findings of E.W. Berry at this particular site have been noted as being somewhat unreliable. The presence of Malvaceae at Laguna del Hunco was recently confirmed by pollen assigned to the subfamily Tilioideae. Previously described macrofossils of the subfamily Malvoideae found in the Southern Hemisphere is limited to Bastardiopsis (wood); thus, these newly described Laguna del Hunco infructescences may represent the first known Malvoideae fossil fruits of the Southern Hemisphere.

1 - Cornell University, Plant Biology, LH Bailey Hortorium, Mann Library, Cornell University, Ithaca, NY, 14850, USA
2 - Penn State University, Geociences, Pennsylvania State University, University Park, PA, 16802, USA


Presentation Type: Oral Paper
Number: PB2004
Abstract ID:265
Candidate for Awards:Isabel Cookson Award,Maynard F. Moseley Award

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