Laurenciella, IN

Popolizio, Thea R., Schneider, Craig W., Jongbloed, Walter M., Saunders, Gary W. & Lane, Christopher E., 2022, Molecular analysis resolves the taxonomy of the Laurencia complex (Rhodomelaceae, Ceramiales) in Bermuda and uncovers novel species of Chondrophycus and Laurenciella, Cryptogamie, Algologie 20 (1), pp. 1-30 : 17-18

THE GENUS LAURENCIELLA IN BERMUDA

The genus Laurenciella was segregated from Laurencia ( Cassano et al. 2012b) on the basis of molecular sequence data, which showed it to be a distinct clade despite its generic features being indistinguishable from those of Laurencia . The type of the genus, Laurenciella marilzae (Gil-Rodriguez, Sentíes, Diaz-Larrea, Cassano & M.T.Fujii) Gil-Rodriguez, Sentíes, Diaz-Larrea, Cassano & M.T.Fujii ,was originally described from the Canary

Islands ( Gil-Rodriguez et al. 2009, as Laurencia marilzae Gil-Rodriguez, Senties, Díaz-Larrea, Cassano & M.T.Fujii ) based on rbc L sequences and characterized morphologically by the distinctive yellow-orange color of its habit ( Fig. 4A), cortical cells that project markedly in cross-section, and the presence of ‘ corps en cerise ’ in all cells of the thallus. Corroborating evidence from both molecular and morphological analyses of specimens collected in the Mexican Caribbean showed that this species was also present in the tropical western Atlantic Ocean ( Sentíes et al. 2011). More recently, a second species from the genus, L. mayaimii Collado-Vides, Cassano & M.T.Fujii , was described from Florida ( Collado-Vides et al. 2018).

Our molecular findings show a clear relationship between Laurenciella marilzae and specimens that we collected in Bermuda and the Florida Keys. Both genetic variation (3.9% divergence in rbc L) and differences in overall habit morphology suggested that these latter collections were a distinct second species of the genus, described herein as L. namii Popolizio, C.W.Schneider & C.E.Lane , sp. nov. Not excepting the shared features of Laurenciella and Laurencia sensu stricto (i.e., four pericentral cells in axial segments; presence of ‘ corps en cerise ’; presence of secondary pit connections), microscopic vegetative characters of L. marilzae and L. namii sp. nov. predominantly overlap ( Table 5). In particular, the size and shape of outer cortical cells ( Fig. 4D, F), the size and shape of medullary cells ( Fig. 4E), the conspicuous projecting of cortical cells in cross-section ( Fig. 4D) and the presence of trichoblasts with 3-4 orders of subdichotomous branching all represent shared characteristics ( Fig. 4F, G). In addition, Bermuda and the Florida Keys specimens of L. namii sp. nov. are distinctly yellow-orange in color ( Fig. 4A, B), an identifying feature that is noted for specimens of L. marilzae from the type locality and from the Caribbean Sea. However, this does not appear to be a characteristic of the genus as a whole because deepoccurring Brazilian specimens ( Rocha-Jorge et al. 2010), as well as an undescribed genetic isolate ( Laurenciella sp. 1 Bda; Fig. 1), are markedly red in color.

Though the vegetative anatomy appears to be largely cryptic between Laurenciella marilzae and L. namii sp. nov., the two species are quite distinct in overall habit. Laurenciella namii sp. nov. reaches twice the height of L. marilzae and has a thallus texture that is fleshy rather than cartilaginous. The main axes of L. namii sp. nov. are slender and are distinctly lax ( Fig. 4A), never displaying the characteristic “turf ” form possessed by L. marilzae in the Caribbean ( Sentíes et al. 2011). Branching patterns in L. namii sp. nov. are more irregular than alternate ( Fig. 4A, B), with upper portions of the thallus tending to be profusely branched, whereas lower portions are often denuded at maturity ( Fig. 4A). The habitats of both Caribbean and Canary Islands specimens of L. marilzae are documented as exposed sites in the low intertidal zone ( Gil-Rodriguez et al. 2009, Sentíes et al. 2011). Our collections of L. namii sp. nov. from Bermuda and Florida are exclusively found in the subtidal and are especially common in shallow, relatively protected habitats at both locations.

Therefore, after a thorough assessment of species in the ‘ Laurencia -complex’ from the western Atlantic, we determined that our specimens of Laurenciella namii sp. nov. are unique. We did consider the historical name Laurencia obtusa var. gracilis (C.Agardh) Kützing based on the illustrations and description of Kützing (1865), which we interpreted as “delicate branches spreading widely,” and ofCollins & Hervey (1917) who describe it as a “delicate, soft and slender form.” Without seeing the original Chondria obtusa var. gracilis in Lund that Agardh (1822) reported from the West Indies, we believe linking this variety to the new species of Laurenciella would be unwise at present. We did not observe Laurencia obtusa var. gracilis in our collections from St. Croix in the West Indies, the type locality of this variety. Interestingly, images of specimens from Bermuda with the characteristics of Laurenciella namii sp. nov., also previously identified as Laurencia obtusa , can be found illustrated on the Macroalgal Herbarium Portal (https://macroalgae.org/portal/collections/ index.php), so this large species in the complex has been an important member of the flora as long as specimens have been collected in the islands.

A second genetically distinct species of Laurenciella from Bermuda has been discovered in this study. Based on rbc L sequences, the closest neighbor to ‘ Laurenciella sp. 1 Bda’ ( Fig. 1) is an undescribed specimen from Brazil, Laurenciella sp. 2 ( Cassano et al. 2012b) from which it differs by 0.4%. These likely represent a single species of Laurenciella with a broad distribution in the western Atlantic. A second undescribed species from Brazil, Laurenciella sp. 3 ( Cassano et al. 2012b) is closely related to these, with 0.9% divergence in rbc L. As with Yuzurua sp. 1 Bda, we have confirmed only a single collection representing this taxon.