Dolichospermum (Ralfs ex Bornet & Flahault) P. Wacklin, L. Hoffmann & J. Komárek

Mcgregor, Glenn B. & Sendall, Barbara C., 2021, True branching and phenotypic plasticity in the planktonic cyanobacterium Dolichospermum brachiatum sp. nov. (Nostocales, Aphanizomenonaceae), from south-eastern Australia, Phytotaxa 491 (2), pp. 93-114 : 105

Dolichospermum (Ralfs ex Bornet & Flahault) P. Wacklin, L. Hoffmann & J. Komárek , emend. G.B. McGregor & B.C. Sendall

Emended description:— Filaments planktonic, solitary or aggregated into floccose masses; trichomes isopolar, uniseriate with facultative T-type true branching, metameric with respect to the position of heterocytes, straight, flexuous, circinate, spirally coiled or irregularly twisted, constricted at the cross walls, without firm sheaths, generally with fine diffluent mucilage. Vegetative cells spherical, ellipsoidal, barrel-shaped, quadrate or cylindrical, with aerotopes. Apical cells undifferentiated, morphologically similar to the vegetative cells. Heterocytes intercalary, solitary, exceptionally in pairs; developing from vegetative cells in ± metameric position. Akinetes spherical to cylindrical in shape, developing paraheterocytically, rarely adjacent to heterocytes, generally separated from them by one or more cells, solitary or in series. Mature akinetes usually three or more times larger than vegetative cells.

Dolichospermum brachiatum G.B. McGregor & Sendall , sp. nov. ( Figs. 1–2 , 4 )

Diagnosis:— Filaments planktonic, generally straight, and surrounded by a broad hyaline mucilage up to 6.5 µm wide; facultatively produce T-type true branching ( Fig 2 ). Branching is homothallic, progressing from a lateral bulge in vegetative cells perpendicular to the main filament, and through subsequent cell divisions, continue to elongate; vegetative cells of branches generally similar to, or only slightly broader than the parent filament, apical cells barrelshaped and hyaline. Vegetative cells with aerotopes, ± vacuolate, longer than broad (L: W 1.9 –6.3) ranging from short cylindrical to elongated club-shaped; 7.7–21.1 µm long × 2.8–5.2 µm broad. Apical cells ± hyaline, elongated and club-shaped (L: W 2.6 –6.5); 10.8–47.8 µm long × 2.6–7.3 µm broad. Heterocytes spherical to slightly longer than broad; 5.4–11.2 µm long × 4.4–7.5 µm broad. Akinetes solitary or up to two in series, and remote from heterocytes; ovate to elongated cylindrical (L: W 1.2 –4.2); rounded at the ends; 13.1–33.8 µm long × 6.3–10.9 µm broad ( Figs 1 & 4 ).

Etymology:— The epithet is from the Latin brachiatus – branched, in reference to the facultative formation of true branching.

Holotype:— Preserved specimen deposited in the Queensland Herbarium ( BRI), accession number AQ1018975.

Type locality:— Waranga Basin , Victoria, Australia (36°33.18’S; 145°6.0’E) .

Gene sequences:— 16S–23S rRNA gene sequences–GenBank Accession Nos. MT 535756 , MT 535757 , MT 535758 , MT 535759 .

Figures

FIGURE 1. Morphology of Dolichospermum brachiatum from Waranga Basin. Scale bars = 20 μm.

FIGURE 2. Sequence of development of T-type true branching of Dolichospermum brachiatum from Waranga Basin. Scale bars = 20 μm.

FIGURE 4. Morphology of Dolichospermum brachiatum strain WB 20619 C1 grown in BG-11 0. Scale bars = 20 μm.