The Systematics and Evolution of Gymnosperms with an Emphasis on a Few Problematic Taxa

Area of Science:

• Botany
• Evolutionary Biology
• Phylogenetics

Background:

• Gymnosperms, including cycads, Ginkgo, conifers, and gnetophytes, have a long evolutionary history marked by diversification and extinction.
• Systematic relationships among extant gymnosperms have been historically debated due to differing character emphasis.

Purpose of the Study:

• To review historical opinions on gymnosperm systematics.
• To re-evaluate key morphological characters within a modern phylogenomic framework.
• To provide a revised classification based on current phylogenetic understanding.

Main Methods:

• Phylogenomic analyses of extant gymnosperm groups.
• Comparative morphological analysis of key reproductive and vegetative traits.
• Review of historical taxonomic literature and systematic opinions.

Main Results:

• Cycads are classified into two families: Cycadaceae and Zamiaceae.
• Ginkgo is sister to cycads, with similarities to conifers attributed to parallel evolution.
• Conifers are paraphyletic, with gnetophytes nested within, indicating gnetophytes are derived conifers.
• Fleshy cones evolved multiple times within conifers; Podocarpaceae are sister to Araucariaceae.
• Cephalotaxaceae and Taxaceae form a clade sister to Cupressaceae, with distinct characteristics.

Conclusions:

• The study clarifies the phylogenetic positions of major gymnosperm groups, including Ginkgo and gnetophytes.
• Phylogenomic data resolve long-standing systematic debates and highlight instances of parallel evolution.
• A revised classification of gymnosperms is proposed, reflecting their evolutionary history and relationships.