On the utility of mucilage ducts as a taxonomic character in Laminaria and Saccharina (Phaeophyceae) – the conundrum of S. groenlandica

Abstract:

We used a combination of molecular and morphological tools to determine whether mucilage ducts are a useful taxonomic character for species differentiation in the genera Laminaria and Saccharina in the North Atlantic and to verify the taxonomic status of Saccharina groenlandica and the genetic species currently attributed to it in North America (NAGenSp). Microscopic examination of genetically verified Laminaria digitata, Laminaria hyperborea, Saccharina latissima and the NAGenSp determined that the presence/absence of mucilage ducts in the blade is not a useful taxonomic character. However, the presence/absence and location of mucilage ducts in the stipe were useful for species differentiation. Laminaria digitata and S. latissima lacked mucilage ducts in the stipe, while the NAGenSp had mucilage ducts in the cortex, and L. hyperborea had mucilage ducts in the medulla. Microscopic examination of the type material of S. groenlandica determined that S. groenlandica is synonymous with S. latissima and that the reportedly diagnostic appearance of mucilage ducts in the stipe and blade of type material were the result of pseudo-mucilage ducts (putative infections). Microscopic examination of the type material of Laminaria nigripes revealed a combination of mislabelled L. digitata and a single specimen that matched the type description, as well as northern individuals of the NAGenSp necessitating the combination Saccharina nigripes (J. Agardh) Longtin et G.W. Saunders comb. nov. Saccharina nigripes is distributed throughout the Northeast Pacific, Canadian Arctic, Northwest Atlantic, and Northern Europe (Greenland, Iceland, and Scandinavia).

Key Words::

• biogeography
• kelp
• Laminaria
• Saccharina groenlandica
• Saccharina nigripes
• taxonomy

ACKNOWLEDGEMENTS

We thank the staff at the Copenhagen University Herbarium, specifically Ruth Nielsen, Peer Corfixen and Dr. Nina Lundholm for allowing us to sample Rosenvinge's type collection of Saccharina groenlandica along with other Laminariaceae from Northern Europe. We also thank the staff at the Lund Herbarium, especially Patrik Fröden, for allowing us access to the type material of Laminaria nigripes. We thank Dr. David Garbary for providing accommodation and hospitality in Digby Neck, Nova Scotia. Samples collected in Acadia National Park are under permit ACAD-2012-SCI-0013. This study was made possible by a scholarship to C. Longtin from the Natural Sciences and Engineering Research Council (NSERC, Canada) and a grant from the International Phycological Society, as well as a NSERC grant awarded to G.W. Saunders.

SUPPLEMENTARY DATA

Supplementary data associated with this article can be found online at http://dx.doi.org/10.2216/15-19.1.s1.