New physaloid fruit‐fossil species from early Eocene South America

Abstract

PREMISE: Solanaceae is a scientifically and economically important angiosperm family with a minimal fossil record and an intriguing early evolutionary history. Here, we report a newly discovered fossil lantern fruit with a suite of features characteristic of Physalideae within Solanaceae. The fossil comes from the early Eocene Laguna del Hunco site (ca. 52 Ma) in Chubut, Argentina, which previously yielded the only other physaloid fruit fossil, Physalis infinemundi. METHODS: The fruit morphology and calyx venation pattern of the new fossil were compared with P. infinemundi and extant species of Solanaceae. RESULTS: Physalis hunickenii sp. nov. is clearly distinct from P. infinemundi in its fruiting calyx with wider primary veins, longer and thinner lobes, and especially in its venation pattern with high density, transverse tertiary veins; these features support its placement in a new species. In comparison with extant physaloid genera, the calyx venation pattern and other diagnostic traits reinforce placement of the new fossil, like P. infinemundi, within the tribe Physalideae of Solanaceae. CONCLUSIONS: Both species of fossil nightshades from Laguna del Hunco represent crown-group Solanaceae but are older than all prior age estimates of the family. Although at least 20 transoceanic dispersals have been proposed as the driver of range expansion of Solanaceae, the Patagonian fossils push back the diversification of the family to Gondwanan times. Thus, overland dispersal across Gondwana is now a likely scenario for at least some biogeographic patterns, in light of the ancient trans-Antarctic land connections between South America and Australia.

Diversity and Conservation Gap Analysis of the Solanaceae of Southern South America

“…This is especially relevant in southern South America, a territory recognized as especially important in the evolution of diverse families, such as Solanaceae, Bignoniaceae, Verbenaceae, Asteraceae, Orchidaceae ( Olmstead, 2013 ; Ulloa Ulloa et al, 2017 ). In southern South America, the wide geographic distribution of the family Solanaceae and its taxonomic richness is partly explained by a long evolutionary history since the early Eocene ( Dupin et al, 2017 ; Deanna et al, 2020 ).…”

“…Of special interest for plant conservation at a continental and subcontinental scale are several angiosperm groups that exhibit early diversification in South America, including the Bignoniaceae, Verbenaceae, Asteraceae, and Solanaceae ( Olmstead, 2013 ; Dupin et al, 2017 ; Deanna et al, 2020 ). Obtaining a comprehensive understanding of the diversity and distribution of these taxa in South America is a challenge, but this effort is paramount to guide future conservation efforts.…”

Evolution and development of inflorescences and floral symmetry in Solanaceae

“…Based on the molecular phylogeny and fossil evidence, the crown‐group age of Solanaceae is estimated to be ca. 60–30 million years ago (Mya) (summarized by Stevens [2001 onward]; also see the discovery of early Eocene fossils [52.5 Mya] of Physalis infinemundi Wilf and Physalis hunickenii Deanna, Wilf & Gandolfo from Argentina [Wilf et al, 2017; Deanna et al, 2020]), and much of the later radiation of the group appears to be primarily centered in South America (Olmstead, 2013; Dupin et al, 2017). Sixteen of the 19 recognized clades are represented in the New World, and all of these 16 clades have South American representatives (Olmstead, 2013).…”

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

“…However, the presence of lineages with New World affinities such as Physalis (Solanaceae; Wilf et al, 2017a;Deanna et al, 2020), at Laguna del Hunco suggest that the composition of the LH paleoflora is not entirely contained in any single modern region (Merkhofer et al, 2015).…”