Corynecladia millarii sp. nov.

(Figs 3-5)

Plants red in colour, soft in texture, forming tufts up to 7 cm high; thalli terete up to 1 mm in diameter, arising from a discoid holdfast with secondary stoloniferous branches; branching irregularly alternate, usually with 2(3) orders of branches; ultimate branchlets are cylindrical-clavate; four periaxial cells per vegetative axial segment. Secondary pit-connections between cortical cells localized in middle to inner part of the cells. Cortical cells with one (rarely two) corps en cerise. No lenticular thickenings. Tetrasporangia in parallel arrangement cut-off abaxially from the third and fourth periaxial cells. It differs from other species of Corynecladia in showing neither secondary cortication nor starch grains in medullary cells and from genera Laurencia and Laurenciella in the occurrence of deep secondary pit connections between cortical cells. It differs from the related C. mediterranea mainly in different molecular sequences.

TYPE MATERIAL. — Italy • Sicily, Syracuse, Capo Murro di Porco; 37°00’37”N, 15°18’28”E; epilithic; 0.1 m depth; 13.III.2021; D. Serio; holotype (tetrasporophyte): CAT [CAT 2721]; GenBank: OQ738957, OQ738958 • ibid.; isotypes: CAT [CAT 2722, CAT 2723]; GenBank: OQ738959, OQ738960, OQ738961, OQ738962 • ibid.; 15.III.2007; paratype (tetrasporophyte): CAT [CAT 2063]; GenBank: OQ738952 • ibid.; 25.IV.2021; paratype (tetrasporophyte): CAT [CAT 2727].

TYPE LOCALITY. — Italy, Sicily, Syracuse, Capo Murro di Porco.

ETYMOLOGY. — The specific epithet is in honor of the late friend and colleague Dr Alan Millar from Sydney, Australia.

DISTRIBUTION. — Type locality and probably more widely distributed.

HABITAT. — Plants epilithic in upper subtidal up to 1 m depth.

DESCRIPTION

Plants epilithic, soft, red and up to 7 cm high.Terete throughout, attached to substrate by a discoid holdfast with stolon-like branches and smaller discoid holdfasts (Fig. 3A, B). Erect axes, 1 mm in diameter in the middle portion of the thallus, irregularly alternately branched, usually with 2(-3) orders of branches. Branchlets with slight epidermal cell projection near the apex (Fig. 4A). Cortical cells with one (rarely two) corps en cerise (Fig. 4B). In transverse section cortical cells quadratic to rectangular, not radially elongated nor arranged as a palisade, measuring 20-25 ×15-20 µm in the middle portions of the plant (Fig. 4C). Cortical cells connected to each other by thin secondary pit-connections. In longitudinal section these secondary pit-connections localized in the middle to inner part of the cells (Fig. 4D) making them hardly visible in surface view. Medullary cells rounded, 35-40×25-30 µm in the middle portions of the thallus, larger toward the centre. Walls of medullary cells without lenticular thickenings (Fig. 4C). Each vegetative axial segment cuts off four periaxial cells (Fig. 5B). Tetrasporangial initials cut off abaxially from the third and fourth periaxial cells (Fig. 5A, B). No additional tetrasporangial periaxial cells produced. Mature tetrasporangia tetrahedrally divided, measuring 60-70 µm in diameter. Tetrasporangia in a parallel arrangement along the axis of the stichidium (Fig. 5C). Gametangia unknown.