Evolution and systematics of Australian Casearia Jacq. (Salicaceae), with two new species and one new subspecies described from North Queensland

Casearia (Salicaceae) is a pantropical genus consisting of ~200 accepted species, 5 of which occur in Australia in addition to 3 putative undescribed taxa. In this study, we use Angiosperms353 target capture loci to reconstruct the evolutionary relationships of Casearia in Australia and test whether the putative new entities warrant formal description. Our results support previous work showing that a monophyletic Casearia originated in the Neotropics before entering the Palaeotropics. Species distributed in South-east Asia render the Australian species paraphyletic, providing preliminary evidence that the genus likely entered Australia more than once and that hybridisation may have played a role in at least one clade. Finally, we synthesise our molecular and morphological evidence to describe three new taxa for Australia: Casearia cordatella W.E.Cooper, sp. nov., C. laccata W.E.Cooper, sp. nov. and C. costulata subsp. triplinervis W.E.Cooper & Joyce, subsp. nov. We propose that Casearia costulata subsp. triplinervis is the product of budding speciation in the Windsor and Carbine Uplands of Queensland. For each new taxon, photographs and notes on habitat and distribution are provided, and an identification key for all Australian taxa is included.