AbstractProblems with the name and concept of the entity known as “Porphyra umbilicalis” that have led to confusion over its identity for more than 250 years are addressed. The name was first used by Kützing (1843), who provided a diagnosis based entirely on material collected from Scotland by Scheele, but he later subsumed it under another species. Jacob Agardh (1883) transferred Ulva umbilicalis L. (1753) to Porphyra. We show that this nomenclatural problem can be resolved by typifying the names Ulva umbilicalis L. and Porphyra umbilicalis Kütz. Although we have located a Scheele specimen of Porphyra, there is no evidence that Kützing based his description of P. umbilicalis on this material. We have therefore selected a specimen of P. umbilicalis from Scotland as neotype of P. umbilicalis Kütz. which fits both his diagnosis and the current concept of P. umbilicalis and for which we have molecular data. We also provide a revised diagnosis and designate the specimen chosen as the neotype of P. umbilicalis Kütz. as the epitype of Ulva umbilicalis L.
