Saccharina compla(nada?) Species Determining the validity of S. complanata as a distinct species

Abstract

The kelp species Saccharina complanata (order Laminariales, family Laminariaceae) originally described as Saccharina latissima f. complanata, is a poorly understood species, often overlooked in studies involving other Saccharina species, such as Saccharina latissima, commonly known as ‘sugar kelp’. S. complanata is morphologically distinguished from S. latissima through a longer, complanate stipe (typically >30 cm). Owing both to the morphological plasticity of Saccharina species and a paucity of morphological and genetic data surrounding S. complanata, many phycologists continue to question the validity of S. complanata as a species. To address this I sequenced the nuclear-encoded rRNA internal transcribed spacer (ITS) 1 & 2 regions of over 20 alga that presented morphologically as S. latissima or S. complanata and compared them to existing ITS sequences of species within order Laminariales using a maximum likelihood phylogenetic tree. Here I show that, unexpectedly, S.complanata shares a close genetic relation to the kelp Pleurophycus gardneri (family Alariaceae). I debate whether the genetic similarities of the ITS 1 & 2 regions of P. gardneri and S.complanata indicate complanata as a new Pleurophycus species or variational form of P. gardneri. This preliminary data strongly suggests that deeper genetic investigations and potential reorganizations of the Pleurophycus genus to include S. complanata are necessary.