We review the occurrence of the diatom genus Actinella Lewis in Hawai‘i. Based on collections from the islands of Kaua‘i, Moloka‘i, and Hawai‘i, we have documented the presence of three species of the genus. Using light and scanning electron microscopy, we illustrate these species, two of which are new to science and described here. Actinella punctata Lewis is distinct in having a bulbous headpole with a short extension at the dorsal margin and a large extension on the ventral margin. This species was observed from Hawai‘i and Moloka‘i. Actinella hawaiiensis Ripple & Kociolek, n. sp., is distinguished by its headpole extension being produced from the dorsal margin, whereas A. molokaiensis Ripple & Kociolek, n. sp., has a headpole protuberance near the center of the apex. Both of the new species are found on the islands of Kaua‘i and Molokai‘i. A previously described endemic, A. punctata var. alakaiensis Main, was not encountered in our collections. Three of the four Actinella taxa from Hawai‘i are currently known as endemics and appear to have their closest allies in either North and /or South America, similar to observations for Gyrosigma krammeri Kociolek et al., another diatom species in Hawai‘i. Further research is necessary to determine the biogeographic patterns of the freshwater diatom flora of Hawai‘i.


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pp. 609-621
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