Dubautia haupuensis, a new species of the Hawaiian silversword alliance (Compositae--Madiinae) from Hā'upu, Kaua'i

Dubautia haupuensis B.G.Baldwin & K.R.Wood is newly described from windswept ridgelines near the summit of Hāʻupu, Kauaʻi, in the Hawaiian Islands, where only two clusters of plants are currently known. Based on molecular phylogenetic data, this highly endangered shrub of the Hawaiian silversword alliance belongs to a recently resolved clade of endemic Kauaʻi taxa, mostly from wet or bog habitats, including D. imbricata subsp. acronaea, D. imbricata subsp. imbricata, D. kalalauensis, D. kenwoodii, D. laevigata, D. syndetica, and D. waialealae. Unlike its close relatives and other members of Dubautia, D. haupuensis has the following unique combination of morphological characteristics: well-branched shrubs with leaves opposite, sessile, and glabrous, leaf venation ± parallelodromous, with 5 to 9 basal nerves, capitulescences densely corymbiform to paniculiform, peduncles hirsute, peduncular bracts lance-linear to ovate, with faces glabrous and margins ciliate, heads 7 to 12-flowered, paleate throughout, the paleae each partially clasping a floret, with faces glabrous and distal margins ciliate, corolla tube/throat sessile-glandular, the throat dilated ≤ 2' tube width, and pappus ± equaling corolla, of 20 to 31 setiform to narrowly subulate, densely ciliate scales, the cilia < 0.5 mm long. It also is distinguished from all other taxa of the silversword alliance by diagnostic nuclear ribosomal DNA nucleotide states. Six of the seven taxa that constitute a clade with D. haupuensis have highly restricted distributions on Kauaʻi and are of significant conservation concern, as reflected by listing most of them as Endangered by the U.S. Fish and Wildlife Service. Dubautia haupuensis is also exceedingly rare and in need of immediate conservation action to prevent its extinction. Invasive plants (especially melastomes), potential ungulate activity, lack of opportunity for outcrossing, and any mortality from stochastic events are major threats to the species, in addition to possible impacts of anthropogenic climate change.

Methods
The DNA sequences aligned here using MAFFT (nexus file) represent the non-identical nuclear ribosomal DNA sequences published by Baldwin et al. (2021) American Journal of Botany 108: 2015-2037 plus novel external and internal transcribed spacer region sequences for the newly described species, Dubautia haupuensis, which were the result of Sanger sequencing (using the same methods as in Baldwin et al. (2021). The two tree files are from a maximum likelihood (ML) analysis and a separate phylogenetic analysis using Bayesian inference (BI). ML analyses were run using IQ-TREE 1.6.12 (Nguyen et al. 2015), with nucleotide substitution models for combined-spacer and for 5.8S gene partitions selected using ModelFinder (Kalyaanamoorthy et al. 2017), as in Baldwin et al. (2021). BI analyses were run using MrBayes 3.2.7a (Ronquist et al. 2012) on the CIPRES Portal (Miller et al. 2010), with model selection of K80+G for spacers and K80+I for 5.8S gene (20 million generations, 2 runs, 3 hot chains + 1 cold chain, and 0.25 burnin).