Abstract Detail

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

Atkinson, Brian A. [1].

Early diverging asterids: Paleontological evidence supporting the Late Cretaceous diversification of Cornales.

Cornales is the earliest diverging order within one of the most diverse clade of angiosperms, the asterids (>80,000 species). Characterizing the early evolutionary patterns of this clade is crucial for understanding the initial diversification of asterids. Fossil evidence and divergence time estimates based on molecular data suggest that the Cornales diverged and rapidly radiated during the Late Cretaceous. Due to this rapid radiation, phylogenetic relationships among major lineages within the order are uncertain. Our ability to test phylogenetic hypothesis using paleontological methods is hindered by insufficient sampling of the Cretaceous cornalean fossil record. This study is part of a broader initiative to resolve deep-node cornalean phylogenetic patterns and relationships. Two permineralized cornalean fruits from the lower Campanian (~82 Ma) of Washington State were prepared using the cellulose acetate peel technique and studied anatomically. One specimen was three-dimensionally reconstructed using ImageJ software. The fruits are ellipsoid (at least 16 cm long and 8 cm wide) and consist of valvate endocarps with some remnants of mesocarp. The valves extend along most of the endocarp length and have vertical ridges on the exterior surface. The endocarps are tetralocular with crescent shaped locules in cross section. The valve tissue consists of isodiametric sclereids and a large number of secretory cavities with epithelial linings. The septae are composed of transversely elongated fibers and a number of secretory cavities. In each septum there are typically two rows of vascular bundles that extend the length of the fruit that are surrounded by longitudinally elongated fibers. The locules are lined with an inner epidermis that is made up of longitudinally elongated fibers. Each locule contains one orthotropous unitegmic seed. The fossil fruits display a mosaic of characters that are representative of Cornaceae, Nyssaceae, Davidiaceae, and Mastixiaceae. Based on locule shape, valve morphology, endocarp histology, and vasculature, the fossil fruits are most similar to the “Nyssoid/Mastixioid” lineage (Nyssaceae, Davidiaceae, and Mastixiaceae). However, the novel combination of characters suggests that these fossil fruits represent a new taxon within this lineage. These fruits meaningfully broaden our understanding of the early morphological evolution within Cornales and support phylogenetic hypotheses formulated from both morphological and molecular data. In addition, these fossil fruits further illuminate the early stages of asterid evolution.

1 - Oregon State University, Botany And Plant Pathology, 2082 Cordley Hall, Corvallis, OR, 97331, USA

Keywords:
Cornales
Late Cretaceous
Fruit
Asterids
fossils.

Presentation Type: Colloquium Presentations
Session: C6
Location: Salon 5/The Shaw Conference Centre
Date: Wednesday, July 29th, 2015
Time: 1:45 PM
Number: C6002
Abstract ID:380
Candidate for Awards:None