Abstract Detail

Mesozoic and Cenozoic plant evolution and biotic change: A symposium in honor of Ruth Stockey

Wilf, Peter [1], Carvalho, Monica R. [2], Gandolfo, Maria A. [3], Cuneo, N. Ruben [4].

Early Eocene Physalis fruits from Patagonia turn back the clock on evolution of Solanaceae and inflated calyx syndrome.

Dr. Ruth Stockey has contributed numerous earliest records of important angiosperm clades. In her honor, we here report two fruits from the 52.2 Ma Laguna del Hunco fossil-lake beds in Chubut, Patagonia, Argentina. These specimens represent the first reliable pre-Neogene macrofossils, and the only fossil fruits, of the economically, culturally, and scientifically significant family Solanaceae (nightshades, ca. 2,500 species). The compressed fruits feature greatly inflated, five-lobed calyces, one of which is preserved emerging from a long, slender pedicel and surrounding a large, globose berry. These characteristics are found only in Solanaceae and primarily in the derived genus Physalis (tomatillos, ground cherries, ca. 100 species). Several specialized calyx features place the fossils securely in the crown of Physalis, including invaginated base, angled exterior, regularly incised lobes with angled sinuses, distinct secondary and intersecondary veins, and secondary veins forking before the sinus. Our phylogenetic analyses confirm this placement. The fossils are indistinguishable from several living Physalis species, e.g., P. angustifolia Nutt. (Coastal Groundcherry) of the southeastern USA. Their early Eocene age significantly exceeds corresponding molecular divergence estimates, adding to a growing list of Patagonian fossil plants that show this pattern. Our discovery shows an ancient history for the well-studied genetic pathway that controls the inflated calyx novelty, and the large fossil berry strongly suggests an early appearance of animal-Solanaceae mutualisms. The fossils support the classic idea of early Solanaceae diversification in South America, although Antarctica must now be considered due to its contiguity at the time. Their derived evolutionary position demonstrates that crown Solanaceae had evolved and significantly diversified well before final Gondwanan breakup (ca. 45 Ma). The preservation of delicate Physalis fruits indicates that the source plants grew very close to the ancient lake, most likely on beaches or at the mouths of feeder streams. We observe that living Physalis calyces trap air around the berry, allowing the fruits to float for extended periods of time without damage to the seeds. This feature undoubtedly enables dispersal and also explains how the ancient fruits could have reached the deepwater depocenters of the fossil lake before sinking and becoming fossilized. Moreover, Physalis calyces and their air pockets function as ‘umbrellas’ that prevent wetting of the berry during rains. These calyx functions would have been adaptive in the humid, waterside habitats where the ancient groundcherries lived, offering clues to the selective regimes that favored the earliest cases of inflated calyx syndrome.

1 - Penn State Univ., 537 Deike Bldg., University Park, PA, 16802, USA
2 - Cornell University, Dept Of Geosciences, 412 Mann Library Building, Ithaca, NY, 14853, USA
3 - Cornell University, L. H. Bailey Hortorium, 410 Mann Library Building, Ithaca, NY, 14853-4301, USA
4 - Mef Av. Fontana 140, Trelew-Chubut, N/A, 9100, Argentina

Keywords:
solanaceae
Inflated Calyx Syndrome
Eocene
Gondwana
Physalis
fossils
Laguna del Hunco
Patagonia.

Presentation Type: Colloquium Presentations
Session: C6
Location: Salon 5/The Shaw Conference Centre
Date: Wednesday, July 29th, 2015
Time: 2:15 PM
Number: C6004
Abstract ID:483
Candidate for Awards:None