Generic placement in Lobelia and revised taxonomy for New Zealand species previously in Hypsela and Isotoma (Lobeliaceae)

Abstract

A taxonomic revision is presented for New Zealand plants previously included in Hypsela and Isotoma, with four species recognised. The new names and combinations formally made here are all placed in Lobelia. A single dispersal event from Australia to the South Island of New Zealand is inferred to have preceded a radiation into four New Zealand species. Importantly, the four New Zealand species differ from their Australian progenitors by the capsule that is now indehiscent due to loss of the apical valves. The first species to diverge from this lineage was L. ionantha (the new name for Hypsela rivalis), a mid‐elevation species that occupies sites east of the Alpine Fault. A new North Island endem ic L. carens is distinguished from L. ionantha by its usually hairy stems, leaves, and flower parts, and smaller flowers that lack purple‐violet markings. The two newly named South Island species that occur west of the Alpine Fault evidently evolved from a common ancestral species that is inferred to have more narrow leaves, smaller flowers, and a reduced zone of adnation for the epipetalous stamens. One species, L. fatiscens, the name for a species previously identified as the Australian Isotoma fluviatilis, primarily occupies coastal sites, and only tetraploid plants with 2n = 28 are known. The other species, L. fugax, is a newly described upland species endemic to the ephemeral and shallow margins of cirque lakes within Kahurangi National Park in North‐West Nelson. The diploid (2n = 14) L. fugax is like a diminutive version of L. fatiscens, which must have diverged from the common ancestral species before the chrom osome doubling that occurred in the evolution of L. fatiscens. The conservation status of these endemic New Zealand species is evaluated.