Ceramium riosmenae sp. nov. (Ceramiaceae, Rhodophyta): a new complete corticated species on Gracilaria from Baja California Sur, Mexico

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  • ABSTRACT

    Ceramium riosmenae sp. nov. is described from Baja California Sur, Mexico based on morphological and molecular data. The new species is characterized by erect thalli only, penetrating rhizoids on Gracilaria, 7-8 periaxial cells, five corti-cal initials per periaxial cell, complete cortication throughout, an average of 11-12 segments between branching points,rare adventitious branchlets, and cruciate tetrasporangia. Although C. riosmenae sp. nov. is similar to C. interruptum, C. sinicola, and C. codicola reported from Baja California Sur, Mexico in size and habit, it differs from these species in the number of cortical initials, habit, degree of cortication, host, and the shape of rhizoidal tips. C. riosmenae is separated from C. interruptum with interrupted cortication and four cortical initials from C. sinicola with spins near the apex and incomplete cortication near the base and from C. codicola with bulbous rhizoids on Codium. Our rbcL sequences reveal sufficient sequence divergence (2.4-3.9%) between C. riosmenae and C. interruptum, C. sinicola, and C. codicola to war-rant species recognition and to separate C. riosmenae from these species on a phylogenetic tree.


  • KEYWORD

    Ceramium riosmenae sp. nov. Ceramiaceae , morphology , phylogeny , rbcL , Rhodophyta , taxonomy

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  • [Fig. 1.] Ceramium riosmenae sp. nov. (A) Vegetative thallus. (B) Apical regions. (C) Upper thallus part with complete cortication. (D) Lower thallus part with incomplete cortication. (E-G) Cross sectional views through the cortical node of an axis showing the alternate sequence of the eight periaxial cells. (H-K) Sequence information for the five cortical initials from a periaxial cell. (L) Rhizoids showing slender, rod-shaped and non-bulbous rhizoids. (M) Tetrasporangial thallus. (N & O) Detail of cortex showing tetrasporangia completely immersed in upper (N) and middle (O) thallus. (P & Q) Cross sectional views showing alternate sequence of tetrasporangia at the cortical node. (R) A cortical filament showing tetrasporangia produced from periaxial and cortical cells. Ax, axial cell; C1-5, sequence of cortical cell formation; P, periaxial cell; P1-7, sequence of periaxial cell formation; R, rhizoid; T, tetrasporangium. Scale bars represents: A-C, K, M & P-R, 50 μm; E-J, 25 μm; D, L ,N & O, 100 μm.
    Ceramium riosmenae sp. nov. (A) Vegetative thallus. (B) Apical regions. (C) Upper thallus part with complete cortication. (D) Lower thallus part with incomplete cortication. (E-G) Cross sectional views through the cortical node of an axis showing the alternate sequence of the eight periaxial cells. (H-K) Sequence information for the five cortical initials from a periaxial cell. (L) Rhizoids showing slender, rod-shaped and non-bulbous rhizoids. (M) Tetrasporangial thallus. (N & O) Detail of cortex showing tetrasporangia completely immersed in upper (N) and middle (O) thallus. (P & Q) Cross sectional views showing alternate sequence of tetrasporangia at the cortical node. (R) A cortical filament showing tetrasporangia produced from periaxial and cortical cells. Ax, axial cell; C1-5, sequence of cortical cell formation; P, periaxial cell; P1-7, sequence of periaxial cell formation; R, rhizoid; T, tetrasporangium. Scale bars represents: A-C, K, M & P-R, 50 μm; E-J, 25  μm; D, L ,N & O, 100 μm.
  • [Fig. 2.] Ceramium riosmenae sp. nov. (A) Male thallus. (B) Surface of cortex bearing spermatangia on adaxial side. (C) Cross section showing spermatangia developed from cortical cells. (D) Female thallus bearing cystocarps. (E) Apical region bearing procarps on abaxial side. (F) Four-celled carpogonial branch. (G) Formation of auxiliary cell from supporting cell. (H) Formation of gonimoblast initial and foot cell. (I) Formation of first gonimolobe. (J) Mature cystocarp surrounded by involucral branches. Au, auxiliary cell; Ax, axial cell; C, cortical cell; CB1-3, carpogonial branch cells; Cp, carpogonium; Cy, cystocarp; Fu, fusion cell; Ft, foot cell; G, gonimoblast; Gl, gonimolobe; Gli, gonimolobe initial; Iv, involucral branches; P, periaxial cell; S, spermatangium; SPC, spermatangial parent cell; Su, supporting cell. Scale bars represent: A, D, 200 μm; B, E, J, 50 μm; C & F-I, 25 μm.
    Ceramium riosmenae sp. nov. (A) Male thallus. (B) Surface of cortex bearing spermatangia on adaxial side. (C) Cross section showing spermatangia developed from cortical cells. (D) Female thallus bearing cystocarps. (E) Apical region bearing procarps on abaxial side. (F) Four-celled carpogonial branch. (G) Formation of auxiliary cell from supporting cell. (H) Formation of gonimoblast initial and foot cell. (I) Formation of first gonimolobe. (J) Mature cystocarp surrounded by involucral branches. Au, auxiliary cell; Ax, axial cell; C, cortical cell; CB1-3, carpogonial branch cells; Cp, carpogonium; Cy, cystocarp; Fu, fusion cell; Ft, foot cell; G, gonimoblast; Gl, gonimolobe; Gli, gonimolobe initial; Iv, involucral branches; P, periaxial cell; S, spermatangium; SPC, spermatangial parent cell; Su, supporting cell. Scale bars represent: A, D, 200 μm; B, E, J, 50 μm; C & F-I, 25 μm.
  • [Fig. 3.] Ceramium riosmenae sp. nov. (A) Vegetative thallus. (B) Apical region. (C) Cortical node in the middle. (D & E) Cortical filaments showing five cortical initials from periaxial cell. (F) Basal part of erect axis on Gracilaria. (G) Rizoids produced from periaxial and cortical cells. (H) Tetrasporangial thallus. (I & J) Cross sectional views showing tetrasporangial arrangement. (K & L) Cortex showing completely immersed tetrasporangia. (M) Male thallus. (N) Cross section view through axis of male thallus. (O) Surface of cortex bearing spermatangia. (P) Female thallus. (Q) Cross sectional view of female axis with early stage cystocarp. (R) Mature cystocarp surrounded by involucral branchlets. Ax, axial cell; C1-4, sequence of cortical cell formation; Cy, cystocarp; Ft, foot cell; Gl, gonimolobe; Iv, involucral branches; P, periaxial cell; R, rhizoid; S, spermatangium; Su, supporting cell; T, tetrasporangium. Scale bars represent: A, P & Q, 500 μm; B, K & L-O, 100 μm; C, F, G, I, J & N, 50 μm; D & E, 25 μm; H, 700 μm; R, 200 μm.
    Ceramium riosmenae sp. nov. (A) Vegetative thallus. (B) Apical region. (C) Cortical node in the middle. (D & E) Cortical filaments showing five cortical initials from periaxial cell. (F) Basal part of erect axis on Gracilaria. (G) Rizoids produced from periaxial and cortical cells. (H) Tetrasporangial thallus. (I & J) Cross sectional views showing tetrasporangial arrangement. (K & L) Cortex showing completely immersed tetrasporangia. (M) Male thallus. (N) Cross section view through axis of male thallus. (O) Surface of cortex bearing spermatangia. (P) Female thallus. (Q) Cross sectional view of female axis with early stage cystocarp. (R) Mature cystocarp surrounded by involucral branchlets. Ax, axial cell; C1-4, sequence of cortical cell formation; Cy, cystocarp; Ft, foot cell; Gl, gonimolobe; Iv, involucral branches; P, periaxial cell; R, rhizoid; S, spermatangium; Su, supporting cell; T, tetrasporangium. Scale bars represent: A, P & Q, 500 μm; B, K & L-O, 100 μm; C, F, G, I, J & N, 50 μm; D & E, 25 μm; H, 700 μm; R, 200 μm.
  • [Fig. 4.] Phylogenetic tree of Ceramium riosmenae sp. nov. based on the rbcL sequences inferred from maximum likelihood (ML) analyses using the general time reversible model and the gamma distribution. The parameters were as follows: assumed nucleotide frequencies A = 0.3189, C = 0.1584, G = 0.02091, T = 0.3136; substitution rate matrix with A-C substitutions = 1.3033, A-G = 2.6418, A-T = 2.8542, C-G = 0.6370, C-T = 15.1809, G-T = 1.0000; proportion of sites assumed to be invariable = 0 and rates for variable sites assumed to follow a gamma distribution with shape parameter = 0.2013. Bootstrap proportion values (> 50%) for ML (500 replicates).
    Phylogenetic tree of Ceramium riosmenae sp. nov. based on the rbcL sequences inferred from maximum likelihood (ML) analyses using the general time reversible model and the gamma distribution. The parameters were as follows: assumed nucleotide frequencies A = 0.3189, C = 0.1584, G = 0.02091, T = 0.3136; substitution rate matrix with A-C substitutions = 1.3033, A-G = 2.6418, A-T = 2.8542, C-G = 0.6370, C-T = 15.1809, G-T = 1.0000; proportion of sites assumed to be invariable = 0 and rates for variable sites assumed to follow a gamma distribution with shape parameter = 0.2013. Bootstrap proportion values (> 50%) for ML (500 replicates).
  • [Table 1.] Comparison of morphological features among complete corticated Ceramium species
    Comparison of morphological features among complete corticated Ceramium species