J Syst Evol

• Research Article •    

Perianth evolution and implications for generic delimitation in the eucalypts (Myrtaceae), including the description of the new genus, Blakella

Michael D. Crisp1,2*, Bui Q. Minh3, Bokyung Choi2,4, Robert D. Edwards2,5, James Hereward1, Carsten Kulheim2,6, Yen Po Lin1,7, Karen Meusemann8, Andrew H. Thornhill9,10,11, Alicia Toon1, and Lyn G. Cook1   

  1. 1 School of Biological Sciences, The University of Queensland, Brisbane, QLD 4072, Australia;
    2 Research School of Biology, The Australian National University, Canberra, ACT 2601, Australia;
    3 School of Computing, The Australian National University, Canberra, ACT 2601, Australia;
    4 Department of Biological Science, College of Bioscience and Biotechnology, Chungnam National University, Daejeon 34134, Korea;
    5 Colorado Natural Heritage Program, Warner College of Natural Resources, Colorado State University, 1475 Campus Delivery, Fort Collins, CO 80523-1475, USA;
    6 College of Forest Resources and Environmental Science, Michigan Technological University, Houghton, Michigan 49331, United States of America;
    7 Department of Plant Medicine, National Chiayi University, Taiwan, China;
    8 The Leibniz Institute for the Analysis of Biodiversity Change(LIB), Museum Koenig Bonn, Adenauerallee 127, Bonn 53113, Germany;
    9 Australian National Herbarium, CSIRO National Research Collections Australia, Canberra, ACT 2601, Australia;
    10 Department of Environment and Water, School of Biological Sciences, University of Adelaide, Adelaide, SA 5005, Australia;
    11 NCW Beadle Herbarium, School of Environmental and Rural Science, University of New England, Armidale, NSW 2351, Australia
    *Author for correspondence. E-mail:bossiaea@gmail.com
  • Received:2023-03-30 Accepted:2023-10-30 Online:2024-01-23

Abstract: Eucalypts (Myrtaceae tribe Eucalypteae) are currently placed in seven genera. Traditionally, Eucalyptus was defined by its operculum, but when phylogenies placed Angophora, with free sepals and petals, as sister to the operculate bloodwood eucalypts, the latter were segregated into a new genus, Corymbia. Yet, generic delimitation in the tribe Eucalypteae remains uncertain. Here, we address these problems using phylogenetic analysis with the largest molecular data set to date. We captured 101 low-copy nuclear exons from 392 samples representing 266 species. Our phylogenetic analysis used maximum likelihood (IQtree) and multispecies coalescent (Astral). At two nodes critical to generic delimitation, we tested alternative relationships among Arillastrum, Angophora, Eucalyptus, and Corymbia using Shimodaira's approximately unbiased test. Phylogenetic mapping was used to explore the evolution of perianth traits. Monophyly of Corymbia relative to Angophora was decisively rejected. All alternative relationships among the seven currently recognized Eucalypteae genera imply homoplasy in the evolutionary origins of the operculum. Inferred evolutionary transitions in perianth traits are congruent with divergences between major clades, except that the expression of separate sepals and petals in Angophora, which is nested within the operculate genus Corymbia, appears to be a reversal to the plesiomorphic perianth structure. Here, we formally raise Corymbia subg. Blakella to genus rank and make the relevant new combinations. We also define and name three sections within Blakella (Blakella sect. Blakella, Blakella sect. Naviculares, and Blakella sect. Maculatae), and two series within Blakella sect. Maculatae (Blakella ser. Maculatae and Blakella ser. Torellianae). Corymbia is reduced to the red bloodwoods.

Key words: Angophora, Blakella, classification, Corymbia, Eucalyptus, homoplasy, low-copy nuclear loci, perianth evolution, phylogeny, targeted capture