Reconstructing Dipsacales phylogeny using Angiosperms353: issues and insights.

Area of Science:

• Phylogenetics
• Molecular Evolution
• Angiosperm Systematics

Background:

• Phylogenetic relationships in Dipsacales are poorly resolved using plastid data alone.
• Uncertainty in Dipsacales phylogeny hinders understanding of morphological evolution.
• Key unresolved placements include Heptacodium, Zabelia, and relationships within Caprifolieae and Linnaeeae.

Purpose of the Study:

• To infer the phylogeny of Dipsacales using a large nuclear- $($Hyb-Seq$)$ dataset.
• To estimate divergence times within the Dipsacales clade.
• To resolve phylogenetic uncertainties and inform morphological evolution interpretations.

Main Methods:

• Applied the Angiosperms353 probe set to 96 Dipsacales species for nuclear locus sequencing.
• Inferred phylogenetic trees using RAxML and ASTRAL from nuclear and assembled plastid data.
• Calibrated divergence times using 10 fossil records.

Main Results:

• Nuclear and plastid data confidently place Heptacodium within Caprifolieae, indicating homoplasy in floral and fruit morphology.
• Phylogenetic placement of Zabelia and relationships within Caprifolieae and Linnaeeae remain unresolved.
• Dipsacales diversification initiated earlier than previously estimated, with major splits occurring in the Eocene.

Conclusions:

• The Angiosperms353 probe set effectively generated a large nuclear dataset for Dipsacales.
• Poor resolution persists in clades with low molecular evolutionary rates.
• Future studies should incorporate more variable nuclear loci, including developmental genes, for improved phylogenetic resolution.