Two centuries from species discovery to diagnostic characters: molecular and morphological evidence for narrower species limits in the widespread SW Australian Anarthria gracilis complex (Restionaceae s.l./Anarthriaceae, Poales)

Constantin I Fomichev; Terry D Macfarlane; Carmen M Valiejo-Roman; Tahir H Samigullin; Galina V Degtjareva; Barbara G Briggs; Dmitry D Sokoloff

doi:10.7717/peerj.10935

Two centuries from species discovery to diagnostic characters: molecular and morphological evidence for narrower species limits in the widespread SW Australian Anarthria gracilis complex (Restionaceae s.l./Anarthriaceae, Poales)

PeerJ. 2021 Mar 8:9:e10935. doi: 10.7717/peerj.10935. eCollection 2021.

Authors

Constantin I Fomichev¹, Terry D Macfarlane², Carmen M Valiejo-Roman³, Tahir H Samigullin³, Galina V Degtjareva⁴, Barbara G Briggs⁵, Dmitry D Sokoloff¹

Affiliations

¹ Department of Higher Plants, Biological Faculty, M.V. Lomonosov Moscow State University, Moscow, Russia.
² Western Australian Herbarium, Biodiversity and Conservation Science, Department of Biodiversity, Conservation and Attractions, Kensington, WA, Australia.
³ Department of Evolutionary Biochemistry, A.N. Belozersky Institute of Physico-Chemical Biology, M.V. Lomonosov Moscow State University, Moscow, Russia.
⁴ Botanical Garden, Biological Faculty, M.V. Lomonosov Moscow State University, Moscow, Russia.
⁵ National Herbarium of New South Wales, Royal Botanic Gardens Trust, Sydney, NSW, Australia.

Abstract

Background: The extreme southwest of Australia is a biodiversity hotspot region that has a Mediterranean-type climate and numerous endemic plant and animal species, many of which remain to be properly delimited. We refine species limits in Anarthria, a Western Australian endemic genus characterised by the occurrence of the greatest number of plesiomorphic character states in the restiid clade of Poales. In contrast to many other groups of wind-pollinated Australian Poales, Anarthria was traditionally viewed as having well-established species limits. All six currently recognised species, which are conspicuous members of some Western Australian plant communities, were described in the first half of the 19th century. They are traditionally distinguished from each other mainly using quantitative characters.

Methods: We examined extensive existing herbarium specimens and made new collections of Anarthria in nature. Scanning electron microscopy and light microscopy were used to study leaf micromorphology. Molecular diversity of Anarthria was examined using a plastid (trnL-F) and a low-copy nuclear marker (at103). This is the first study of species-level molecular diversity in the restiid clade using a nuclear marker.

Results: Material historically classified as Anarthria gracilis R.Br. actually belongs to three distinct species, A. gracilis s.str., A. grandiflora Nees and A. dioica (Steud.) C.I.Fomichev, each of which forms a well-supported clade in phylogenetic analyses. Both segregate species were described in the first half of the 19th century but not recognised as such in subsequent taxonomic accounts. Anarthria dioica was first collected in 1826, then wrongly interpreted as a species of Juncus (Juncaceae) and described as Juncus dioicus. We provide a formal transfer of the name to Anarthria and for the first time report its clear and qualitative diagnostic characters: an extremely short leaf ligule and distinctive pattern of leaf epidermal micromorphology. A long ligule is present in A. gracilis s.str. and A. grandiflora. These species differ from each other in leaf lamina morphology and anatomy and have mostly non-overlapping distribution ranges. The narrower definition of species provides a basis for future phylogeographic analyses in Anarthria. Our study highlights a need for more extensive use of nuclear DNA markers in Restionaceae. The use of the low copy nuclear marker at103 allowed a clade comprising all three ligulate species of Anarthria to be recognised. The ligule character is used here for the first time in the taxonomy of Anarthria and merits special attention in studies of other restiids. In general, our study uncovered a superficially hidden but, in reality, conspicuous diversity in a common group of wind-pollinated plants in the southwest of Western Australia.

Keywords: Anarthria; Diagnostic characters; Leaf ligule; Leaf morphology; Micromorphology; Phylogeny; Poales; Restionaceae; South-western Australian biodiversity hotspot; Western Australia.

Grants and funding

The work is supported by the Russian Science Foundation (project 14-14-00250, initial field work of Dmitry D. Sokoloff and Constantin I. Fomichev and identification of the ligule character in 2014–2016; project 19-14-00055, fieldwork of CIF in 2019, micromorphological and molecular analyses and interpretation of data). Electron microscopy was performed using the Unique equipment setup “3D-EMС” of Moscow State University (supported by the Ministry of science and higher education of the Russian Federation, agreement #075-15-2019-1653, unique identifier RFMEFI61919X0014). The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.