Ulva sp.

4.6 Ulva sp. NC 6 - Ulva lactuca

All North Carolina specimens of this species shared an rbc L sequence that was an exact match to that of the U. lactuca specimen from Florida identified by Hughey et al. (2019) as representative for the entire sequence of the lectotype specimen. North Carolina U. lactuca specimens also shared the same tufA sequence as that of the Florida specimen and one of the two ITS sequences was identical to the Florida specimen as well. The other North Carolina U. lactuca ITS sequence was only 3 bp (0.42 %) different. Similar to other studies, U. lactuca is resolved as part of a clade including U. conglobata , U. dactylifera , U. taeniata , U. ohnoi , and U. lacinulata , the latter two species also found in North Carolina. Relationships among the species in this clade were poorly supported in single locus trees generated in this and other studies ( Gabrielson et al. 2024; Hughey et al. 2021b, 2024). However, analyses of Ulva spp. plastid and mitochondrial genomes resolved U. lactuca and U. ohnoi as sister species with full support, and also fully supported a basal position for U. lacinulata within this clade ( Hughey et al. 2024).

Globally, U. lactuca has been confirmed by sequencing to be distributed in the North Atlantic, Mediterranean Sea, Indian and Pacific Oceans. The Linnaeus ’ (1753) original description of U. lactuca mirrors the gross superficial morphology of what was later described as U. fasciata ( Gray 1821) , an alga with strap-like blades all stemming from a centralized stipe at the base that has been synonymized under U. lactuca ( Hughey et al. 2019) . All the collected North Carolina U. lactuca specimens could be interpreted as having the fasciculately branched morphology of U. lactuca , but the states of other characters did not always match the descriptions of U. lactuca (as U. fasciata ) in North Carolina provided by Kapraun (1984) and Schneider and Searles (1991). For example, one of the defining characters of U. fasciata sensu Kapraun (now U. lactuca ) is the presence of very distinct pyrenoids, ranging from 1-3 per cell, a character state that is present in the majority, but not all North Carolina samples of this species.