Taxonomic revision of the Myosotis australis group (Boraginaceae) native to Australia, New Zealand and New Guinea

Abstract

The three main aims of this study were to circumscribe the Myosotis australis R.Br. group, determine the taxonomic utility of pollen characters, and delimit species and revise their taxonomy using macro-morphological and palynological data. The M. australis group is here recircumscribed to comprise two species, M. saxatilis Petrie (Marlborough and Otago, New Zealand) and M. australis. Myosotis australis is a widespread, morphologically variable species with two subspecies. M. australis subsp. australis comprises all Australian and most New Zealand specimens, including M. mooreana Lehnebach, M. lytteltonensis (Laing & A.Wall) de Lange, and several white- or yellow-flowered tag-named taxa from New Zealand, whereas M. australis subsp. saruwagedica (Schltr. ex Brand) Meudt, Thorsen & Prebble, comb. et stat. nov. is endemic to New Guinea. The M. australis group can be distinguished from all other ebracteate-erect Myosotis plants sampled to date, including the Australian endemic, M. exarrhena F.Muell., by a suite of characters, i.e. included anthers, calyx with both retrorse and hooked trichomes, rosette leaf trichomes retrorse abaxially and oblique to the midrib adaxially, and leaf length:width ratio of >2:1. Other characters can distinguish the group from M. discolor Pers., M. arvensis (L.) Hill, and M. umbrosa Meudt, Prebble & Thorsen respectively. Pollen characters were not useful for species delimitation within the M. australis group, but they can help distinguish several species outside it, including natural hybrids of M. australis and M. exarrhena in Australia. Myosotis australis, M. saxatilis and M. exarrhena are included in the taxonomic treatment, whereas introduced species M. discolor and M. arvensis are included in the key only.