Format: ORAL

Chelsea R. Smith1,2, Shannon C. K. Straub3, Tatyana Livshultz1,2

1 Academy of Natural Sciences of Drexel University, Philadelphia, USA 2 Drexel University, Philadelphia, USA 3 Hobart and William Smith Colleges, Geneva, USA

The broad outline of Apocynaceae phylogeny, divided into three subfamilies (Periplocoideae, Secamonoideae, Asclepiadoideae) and two informal grades: rauvolfioids (11 tribes) and apocynoids (9 tribes) has been stable since the earliest single gene plastid analyses: a paraphyletic rauvolfioid grade subtending a monophyletic APSA clade (apocynoids, Periplocoideae, Secamonoideae, Ascelpiadoideae). Accumulation of data, culminating in the first phylogenomic analysis of the family (Antonelli, et al. 2021) has highlighted areas of continued topological uncertainty including relationships within the APSA clade, specifically the positions of Periplocoideae and Rhabdadenieae, and an earlier radiation that includes the rauvolfioid tribes Melodineae, Hunterieae, Amsonieae, and Alyxieae. We revisited Apocynaceae phylogenomics with expanded sampling of taxa and loci (Apoc836; Straub, et al. 2020).  We constructed trees using summary coalescent and concatenation methods and conducted sensitivity analyses to evaluate the robustness of our topologies to sampling and analytical decisions. An intriguing outcome of these analyses is the frequent placement of Periplocoideae as sister to the well-established clade of Baisseeae, Secamonoideae, and Asclepiadoideae, harkening back to the abandoned Asclepiadaceae (comprised of Periplocoideae, Secamonoideae, and Asclepiadoideae) and re-opening questions about homology of pollen aggregation, translators, and coronas in these taxa. This topology is sensitive to both sampling and analytical choices, and we conclude that the weighted ASTRAL analysis most accurately represents remaining uncertainty. This new Apocynaceae species tree suggests a revised classification for the family at the subfamily and tribal levels. Antonelli, A., et al. (2021). Settling a family feud: a high-level phylogenomic framework for the Gentianales based on 353 nuclear genes and partial plastomes. https://doi.org/10.1002/ajb2.1697. Straub, S. C. K., Boutte, J., Fishbein, M., & Livshultz, T. (2020). Enabling evolutionary studies at multiple scales in Apocynaceae through Hyb-Seq. Applications in Plant Sciences, e11400. https://doi.org/10.1002/aps3.11400.