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Dryad

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

Baldwin, Bruce1; Wood, Kenneth2; Fawcett, Susan1

Published May 02, 2024 on Dryad. https://doi.org/10.5061/dryad.k3j9kd5gg

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May 02, 2024 version files 150.80 KB

Abstract

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.