Osmundea sanctarum M.T. Fujii & Rocha-Jorge, 2013

Rocha-Jorge, Renato, Cassano, Valéria, Barros-Barreto, Maria Beatriz, Díaz-Larrea, Jhoana, Sentíes, Abel, Gil-Rodríguez, Maria Candelaria & Fujii, Mutue Toyota, 2013, Osmundea sanctarum sp. nov. (Ceramiales, Rhodophyta) from the southwestern Atlantic Ocean, Phytotaxa 100 (1), pp. 41-56 : 46-48

Osmundea sanctarum M.T. Fujii & Rocha-Jorge , sp. nov. ( Figs. 2–12 , Table 2)

Thalli are red–purple with axes terete, up to 2.5 cm high, cartilaginous in texture and attached to the substratum by a discoid holdfast. Secondary attachments are present. Stoloniferous branches are absent. Thalli are subterete to compressed, 0.92– 1.40 mm wide in the middle portions and cylindrical at the bases with a diameter of 0.96–1.30 mm, and the ultimate branches have a diameter of 0.36–0.43 mm. Branching is sparse, alternate to irregular, and not pinnate. Anastomoses are occasionally present ( Figs. 2, 3 ). First-order branches have a diameter of 0.36–0.63 mm at their bases, 0.55–0.80 mm wide at the middle portions and 0.30–0.40 mm at the apices. Fresh specimens have a strong chemical odor. Transverse sections of the thallus display two cortical layers ( Figs. 4–7 ). The outer layer is composed of translucent (hyaline) cells smaller (diameter of 6–10 µm) than the cells in the inner layer, which has rounded pigmented cells with a diameter of 12–18 µm. ( Figs. 6–8 ). Cortical cells do not form a palisade-like layer, and the secondary pit connections are absent in the outermost cortical cells. Medullary cells are rounded and have a diameter of 15–25 µm. Each vegetative axial segment cuts off two pericentral cells; the first pericentral cell is produced on the side of the trichoblast basal cell ( Fig. 5 ). ‘Corps en cerise’ and lenticular thickenings are absent in living material. Longitudinal sections present cortical cell walls near apices that do not project beyond the surface and apical cells located in depressions from which translucent trichoblasts arise. Tetrasporophytes are composed of simple cylindrical branchlets with a length of 0.3–1.0 mm long and a diameter of 0.1– 0.5 mm ( Figs. 9, 10 ). Tetrasporangia are cut off randomly from the innermost cortical cells and have a diameter of 50–80 µm ( Figs. 11, 12 ). Gametophytes were not found.

Type: — BRAZIL. São Paulo: Laje de Santos Marine State Park , 24° 19’ 2.5” S, 46° 10’ 54.8” W, 18 m depth, coll. R. Rocha- Jorge, M.B. Barros-Barreto, I.B. Silva & M.T. Fujii, 19 April 2012 (holotype SP! 427820. Isotypes MICH!, SPF!, TFC!, UAMIZ!) .

Paratypes: —Laje de Santos Marine State Park, Sul reef (24° 19’ 36.6” S and 46° 11’ 7.8” W) SP! 400134 (as Osmundea sp. ); Laje de Santos Marine State Park, Laje de Santos (24° 19’ 2.5” S and 46° 10’ 54.8” W) SP! 400137, 400547, 427821 (all as Osmundea sp. ).

Distribution and habitat: —Laje de Santos Marine State Park, in Sul reef and Laje de Santos (large rock formation), growing in the subtidal zone (depth of 7–20 m) on rocky substrates associated with other macroalgae species.

Etymology: —The specific epithet sanctarum, Latin for “of the saints,” is derived from the type locality, i.e., Laje de Santos Marine State Park, São Paulo, Brazil.

Phylogenetic analyses: —Parsimony analysis of our dataset produced two equally parsimonious trees, which were 153 steps long and had a consistency index of 0.6. The dataset for rbc L sequences consisted of 700 constant characteristics and 417 parsimony-informative sites.

The topology of the Bayesian tree ( Fig. 13 ) indicated that the Brazilian Osmundea samples formed a distinctive and highly supported monophyletic clade with a sister clade that included samples of O. blinksii (Hollenberg & I.A. Abbott 1965: 1186) K.W. Nam in Nam, Maggs & Garbary (1994: 393), O. sinicola (Setchell & N.L. Gardner 1924: 764) K.W. Nam in Nam, Maggs & Garbary (1994: 393), O. splendens (Hollenberg in Smith & Hollenberg 1943: 219) K.W. Nam in Nam, Maggs & Garbary (1994: 393) and O. spectabilis ( Postels & Ruprecht 1840: 16) K.W. Nam in Nam, Maggs & Garbary (1994: 393). The specimens of Osmundea from Laje de Santos and Parcel do Sul (São Paulo) are molecularly and morphologically identical, which confirms that these samples constitute the same taxonomic entity. The mentioned samples diverged at a high level of genetic variation from the Osmundea spectabilis group (5.4–7.1%), which supports their recognition as a new taxon within the genus Osmundea .

Remarks:—Morphological comparisons of O. sanctarum with other species of Osmundea are shown in Table 2. The interspecific divergence values obtained in this study were similar to those previously reported for the Laurencia complex (Nam et al. 2000, McIvor et al. 2002, Díaz-Larrea et al. 2007, Cassano et al. 2009, 2012a, b, Martin-Lescanne et al. 2010, Rocha-Jorge et al. 2010).

Figures

FIGURE 13. Bayesian phylogram inferred from analyses of rbcL sequences for 35 Laurencia complex taxa and two outgroup species. Numbers above branches correspond to support values for Bayesian inference posterior probability/maximum likelihood bootstrap/ and maximum parsimony bootstrap, respectively. Bold lines indicate a fully supported node in all three analyses. Taxa marked in bold indicate newly determined sequences.

FIGURES 2–8. Osmundea sanctarum: vegetative morphology. Fig. 2. Representative plant. Holotype (SP! 427820) (5 mm). Fig. 3. Detail of a branch with secondary small holdfast (arrow) (2 mm). Fig. 4. Transverse section of the upper portion of a branch (100 µm). Fig. 5. Transverse section showing two axial cells (a), each of which has two pericentral cells (p) and a basal trichoblast cell (bt) (50 µm). Fig. 6. Transverse section of main axes (100 µm). Fig. 7. Detail of transverse section of a branch showing external cortical layer with translucent cells (25 µm). Fig. 8. Translucent cortical cells in surface view (arrows) (25 µm).

FIGURES 9–12. Reproductive morphology of tetrasporangial Osmundea sanctarum plants (SP! 427821). Fig. 9. Tetrasporangial plant showing fertile branchlets (arrows) (3 mm). Fig. 10. Detail of tetrasporangial branchlets (arrows) (1 mm). Fig. 11. Longitudinal section through an apical portion of tetrasporangial branchlet showing tetrasporangia (arrows) originating from cortical cells (100 µm). Fig. 12. Detail of a stalk cell (stk) with two pre-sporangial cover cells (pr), tetrasporangium (te) and one post-sporangial cover cell (po) (250 µm).