Assessment of rhodolith-forming species diversity in British Columbia uncovers novel cryptic diversity in the genera Boreolithothamnion and Rhodolithia gen. nov. (Florideophyceae, Rhodophyta) and the occurrence of hybrid rhodoliths.

Rhodolith collections in British Columbia have historically been limited, and published regional species diversity data are poor. The acquisition of recent collections, notably from rhodolith beds in Haida Gwaii, provided an opportunity to assess diversity in these waters. The DNA barcode markers COI-5P, rbcL-3P, and psbA were used to identify unique genetic groups, which were then placed into a phylogenetic context with other coralline algae and subsequently observed anatomically. These analyses uncovered six rhodolith-forming species: two known, viz. Boreolithothamnion phymatodeum and Boreolithothamnion soriferum; a species provisionally called Boreolithothamnion sp. 1heterocladum; and three novel species described here, viz. Boreolithothamion astragaloi sp. nov., Boreolithothamnion tanuense sp. nov., and Rhodolithia gracilis gen. et. sp. nov., which comprises three varieties. Of particular interest, sequences of the ITS rDNA region showed the variety Rhodolithia gracilis var. gracilis × ramosa var. nov. to be a hybrid of the other two varieties: Rhodolithia gracilis var. gracilis var. nov. and Rhodolithia gracilis var. ramosa var. nov. Although understanding the full extent of BC rhodolith beds will require additional sampling, these findings indicate that rhodoliths are widespread and diverse in British Columbia.