Diversification of crown groupAraucaria: the role ofAraucaria famiisp. nov. in the Late Cretaceous (Campanian) radiation of Araucariaceae in the Northern Hemisphere

Autor: Gar W. Rothwell, Ruth A. Stockey
Rok vydání: 2020
Předmět:
Zdroj: American Journal of Botany. 107:1072-1093
ISSN: 1537-2197
0002-9122
DOI: 10.1002/ajb2.1505
Popis: PREMISE Exceptional anatomical preservation of a fossil araucarian seed cone from a marine carbonate concretion from Vancouver Island, British Columbia, Canada provides unusually complete evidence for cone structure including seeds, megagametophytes, microgametophytes, and embryos of an Upper Cretaceous (Campanian) species of Araucaria, providing important new insights into the structure and relationships of Cretaceous Northern Hemisphere Araucariaceae. METHODS The cone was studied from serial thin sections prepared by the coal ball peel technique. Phylogenetic analysis using a modified morphological matrix with both discrete and continuous characters was performed using TNT version 1.5. RESULTS The nearly spherical cone, 6 × 6 cm in diameter, has helically arranged cone-scale complexes, consisting of a large bract with an upturned tip and a small, fleshy ovuliferous scale. Vascularization of the cone-scale complex is single at its origin. Widely winged bracts, with a bulging base, contain numerous vascular bundles, interspersed with transfusion tissue, and a large number of resin canals. Seeds are ovoid, 1.2 cm long, 1.2 cm in diameter. Nucellus is free from the integument, except at its base, with a convoluted apex, containing possible pollen tubes. Megagametophytes and mature cellular embryos occur in several seeds. CONCLUSIONS This small cone with attached, imbricate leaves, wide bracts, and unusually large seeds, most closely resembles those of Araucaria Section Eutacta. Width and continuity of secondary xylem in the cone axis, and intact cone-scale complexes indicate that this cone probably did not disarticulate readily at maturity. When added to a modified, previously published phylogenetic analysis, Araucaria famii sp. nov. enhances our understanding of the Cretaceous radiation of Northern Hemisphere Araucaria Section Eutacta.
Databáze: OpenAIRE
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