Chondrophycus, 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 : 18-19

THE GENUS CHONDROPHYCUS IN BERMUDA

Our COI-5P and rbc L barcode analyses ( Table 1) uncovered a unique taxon in the genus Chondrophycus from Bermuda, herein described as C. planiparvus Popolizio, C.W.Schneider & C.E.Lane , sp. nov. Sequences from Chondrophycus cf. undulatus (Yamada) Garbary & J.T.Harper and C. dotyi (Y.Saito)

K.W.Nam collected in the Hawaiian Islands, grouped with our new Bermuda species in COI-5P barcode gap analysis ( Table 1). In the rbc L analysis, C. planiparvus sp. nov. differs by only 0.5% from an undescribed specimen collected from Flower Garden Banks, Gulf of Mexico ( Fujii et al. 2006) ( Table 1 and Fig. 1), and these may represent the same species. The two taxa are arranged as a sister grouping to the rest of the Chondrophycus clade, which consists of C. dotyi from Hawaii, C. anabeliae Sentíes, M.T.Fujii, Cassano & Dreckmann from Caribbean Mexico, C. tronoi (E.Ganzon- Fortes) K.W.Nam from the Philippines, C. cf. undulatus from New Caledonia and several undescribed species from South Africa, Australia or New Caledonia. The recently described C. anabeliae from the Caribbean ( Sentíes et al. 2016) has terete axes, but these are occasionally partially compressed. It bears little morphological resemblance to C. planiparvus sp. nov.

Saito (1967) split the genus Laurencia into two subgenera, Laurencia and Chondrophycus , on the basis of tetrasporangial development relative to the axis (parallel or right-angle) and presence or absence of secondary pit connections between cortical cells. He later determined these features were unreliable since some species possessed features of both subgenera, namely, a parallel arrangement of tetrasporangia and lack of secondary pit-connections ( Saito 1982). Species exhibiting this combination of characters would later be attributed to Osmundea (Nam et al. 1994) . Ultimately, Garbary & Harper (1998) elevated the subgenus Chondrophycus to generic rank based on morphological cladistics, including the absence of secondary pit connections.

Nam (1999) proposed an infrageneric classification scheme for Chondrophycus including four subgenera – Chondrophycus, Kangjaewonia , Palisada and Yuzurua . Members of the subgenus Chondrophycus (containing C. cartilagineus (Yamada) Garbary & J.T.Harper as the type, as well as several others) exhibit right-angle development of tetrasporangia but lack secondary pit connections. For species displaying both right-angle arrangement of tetrasporangia and secondary pit connections, Nam (1999) circumscribed the subgenus Yuzurua , which has since been elevated to generic status and is unquestionably distinct from Chondrophycus in phylogenetic analyses ( Martin-Lescanne et al. 2010). Furthermore, Nam (1999) defined the section Parvipapillatae for members of subgenus Yuzurua demonstrating epidermal cell projections at branchlet apices in transverse section, and designated C. parvipapillatus (C.K.Tseng) Garbary & J.T.Harper as the type species of this section. Later, Nam (2006) proposed the genus Palisada following a morphological cladistics analysis that resolved two paraphyletic clades of Chondrophycus species. Chondrophycus parvipapillatus fell into the clade that did not include C. cartilagineus , the generitype, and thus was transferred to Palisada .

Interestingly, our specimens of Chondrophycus planiparvus Popolizio, C.W.Schneider & C.E.Lane , sp. nov. from Bermuda exhibit the three traits that Nam (2006) used to segregate Palisada parvipapillata (C.K.Tseng) K.W.Nam to Palisada : a right-angle arrangement of tetrasporangia, production of secondary pit connections and apical cortical cell projections. Secondary pit connections are noted to be sporadic in P. parvipapillata , but are frequent and conspicuous in C. planiparvus sp. nov., and in the former species, cortical cell projections are present throughout the thallus, whereas these are only occasionally seen in the latter, strictly at branch apices. In our analyses, COI-5P sequence data from a Hawaiian specimen of P. parvipapillata place the species within the genus Palisada ( Table 1), providing molecular evidence for its correct position in the genus and dismissing it as a possible range extension from Bermuda species, despite some morphological similarities.

Table 6 delineates the morphological differences Chondrophycus planiparvus Popolizio, C.W.Schneider & C.E.Lane , sp. nov. has with congeners having compressed or flattened axes. Our Bermuda species is distinguished from these in having upright axes 2 cm long or smaller ( Fig. 5 A-D) and by the conspicuous secondary pit connections present between cortical cells ( Fig. 5D, H), a character that historically has been used to segregate morphological subclades of taxa. Chondrophycus planiparvus sp. nov. represents the only current species of the genus that possesses secondary pit connections. However, this trait is not synapomorphic in other genera in the Laurencia complex, including its sister genus Osmundea . McIvor et al. (2002) suggested that secondary pit connections may be an ancestral state that was subsequently lost in some lineages or species in the complex, a concept that is not easily rationalized given our poor knowledge of pit connection functionality on the whole. Nevertheless, the presence of this character in the Bermuda specimens provides an interesting contrast to other members of the genus. Of the species of Chondrophycus exhibiting compressed axes, only C. kangjaewonii (K.W.Nam & C.H.Sohn) Garbary & J.T.Harper lacks sequence data available from GenBank, but this species is easily distinguished from C. planiparvus sp. nov. by its parallel arrangement of tetrasporangia, which are also three or four times larger.

Notably, all of the compressed species of the genus from the Pacific Ocean are found in intertidal habitats (or shallow subtidal, as in C. kangjaewonii ). Chondrophycus planiparvus Popolizio, C.W.Schneider & C.E.Lane , sp. nov. specimens have been collected exclusively in subtidal waters off the south shore of Bermuda, from depths of 13-23 m during December-March, when water temperatures in Bermuda are at their lowest. These findings suggest that this novel species is adapted to cooler water temperatures and lower light levels than its most similar congeners.