Abstract Detail

Paleobotany

Stockey, Ruth A. [1], Klymiuk, Ashley [2], Rothwell, Gar W. [3].

Structure and homologies of seed enclosing fructifications among Mesozoic “cupulate” gymnosperms.

Ovules of Mesozoic seed plants typically are enclosed by structures that provide protection, facilitate pollination, and aid in dispersal. Whereas the carpel of flowering plants performs these functions within the most species rich clade of plants, seed enclosing structures characterize many Mesozoic gymnospermous clades as well. Several of those bear ovules within a structurally heterogeneous assemblage of organs referred to as cupules, and are commonly referred to as "seed ferns". The Lower Cretaceous (Valanginian) Apple Bay locality on Vancouver Island, Canada has yielded two new morphologies of gymnosperm cupules, Doylea tetrahedrasperma and a second morphotype that reveals that some Mesozoic gymnosperms produced orthotropous radial seeds within uniovulate cupules at the tip of a stem-like organ. These discoveries emphasize the heterogeneity of Mesozoic cupulate fructifications, and prompt an in depth evaluation of structural homologies for all. Diagnostic characters for inferring cupulate organ homologies include radial or bilateral symmetry in the morphology, radial or bilateral symmetry in the anatomy, presence or absence of a bract subtending the cupulate organ, and presence or absence of the diagnostic leaf trace or branch vascular anatomy of the parts of the cupulate organ. Using these criteria, seed cones of conifers and gnetophytes represent compound shoot systems, those of bennettitaleans and cycads represent simple shoots, and those of pentoxylaleans are derived from a single leaf. The seed integument of gnetophytes and a variety of conifers is also enclosed by an additional covering that is equivalent to a whorl of leaves in gnetophytes, but is of equivocal homologies in taxads. Ovulate fructifications of the Early Cretaceous Doyleales and the recently described Geminispermum virginiense consist of seed cones of compound shoot structure with bract-scale complexes that are most similar to those of conifers.   By contrast, those of Caytoniales, Petriellales, Peltaspermales, and Umkomasiales consist of foliar homologues that are considered to be borne on a stem homologue.   This analysis confirms that the morphology and anatomy of cupulate fructifications provide a wealth of characters for resolving relationships among seed plants. Therefore, the thorough description and accurate interpretation of cupulate organs is of particular importance to the resolution of spermatophyte phylogeny.

1 - Oregon State University, Department of Botany and Plant Pathology, Cordley Hall, Corvallis, OR, 97331, USA
2 - Field Museum, Gantz Family Collections Center, 400 Lake Shore Drive, Chicago, IL, 60605, United States
3 - Ohio University and Oregon State University, Environ. & Plant Biol./Botany & Plant Path., Cordley Hall, Crovallis, OR, 97331, USA

Keywords:
Cupulate Gymnosperms
mesozoic
Frond Homologue
Simple Shoot Homologue
Compound Shoot Homologue
Ovulate Fructifications.

Presentation Type: Oral Paper
Session: PL6, Paleobotany: Paleozoic/Mesozoic Paleobotany
Location: /
Date: Thursday, July 22nd, 2021
Time: 10:45 AM(EDT)
Number: PL6004
Abstract ID:301
Candidate for Awards:None