Implications of fossil conifers for the phylogenetic relationships of living families

• Published in: The Botanical review Vol. 65; no. 3; pp. 239 - 277
• Main Author: Miller, C.N. Jr
• Format: Journal Article
• Language: English
• Published: Bronx New York Botanical Garden 01.07.1999; Springer Nature B.V
• Subjects: Bracts; checklists; Cladistics; Conifers; Evaluation; Evolution; Fossils; Genera; literature reviews; old and fossil wood; Paleobotany; Parsimony; Phylogenetics; Phylogeny; Phylogeny (Botany); Pinopsida; plant morphology; Plant phylogeny; species; Taxa; We they distinction; United States
• ISSN: 0006-8101; 1874-9372
• DOI: 10.1007/bf02857631

Fossils have played a central role in our understanding of the evolution of conifers. Interpretation of the seed cone as a compound strobilus and the homologies of the ovuliferous scales of modern conifers with the axillary dwarf shoot of Pennsylvanian forms are based on fossils. Similarly, early evolutionary trends involving the reduction, fusion, and planation of the fertile and sterile elements of the axillary dwarf shoot, leading to structures characteristic of modern families, are documented in Late Permian and Triassic conifers. However, a phylogeny elucidating the derivation of modern families from fossil forms based on shared derived features has been elusive. The present cladistic treatment using 11 characters of ovulate cones and one of pollen grains suggests three phylogenetic groups of Late Paleozoic conifers, represented loosely by the Emporicaceae, Utrechtiaceae, and Majonicaceae of Mapes and Rothwell. The Taxaceae appears to have diverged from ancestors within the Utrechtiaceae, whereas the other modern families owe their origins to the Majonicaceae. The origin of the Taxodiaceae appears to have been biphyletic. Taxodium, Cupressus and Sciadopitys are strongly linked to Dolmitia of the Majonicaceae, but Cryptomeria, Cunninghamia and Araucaria are grouped together and diverge basal to the former taxa. Pinus branches from a position basal to the known genera of the Majonicaceae and all modern families except the Taxaceae. Podocarpus also diverges basal to Majonica but may share an ancestor with this genus; Cepahalotaxus diverges basal to the Dolmitia-Pseudovoltzia subclade but distal to Majonica. Similarly, the Cheirolepidiaceae originated from basal members of the Majonicaceae and shows no close phylogenetic relationship with any modern family. Except for a strong linkage between Cycadocarpidium and the Araucaria-Cunninghamia subclade, genera of the Voltziaceae appear to have branched more or less independently from within the Majonicaceae and show no strong affinity with modern conifers. Thus differences between modern conifer families are due mainly to their divergence from different Paleozoic ancestors.