Gongrosira leptotricha Raineri, 1926

Gongrosira leptotricha Raineri, 1926

Description.

The thallus is encrusted with loose calcium carbonate crystals, forming dark green spherical, hemispherical or slightly irregular plants on stones in running water (Figs 1–3 View Figures 1–4 ). The thallus diameter can attain up to 4 mm (Fig. 4 View Figures 1–4 ). The thallus is composed of prostrate and erect filaments (Figs 5 View Figures 5–9 , 6 View Figures 5–9 ). The prostrate part is creeping, composed of irregularly elliptical or polygonal cells, flattened at the base, which coalesce to form a loose pseudoparenchyma (Fig. 7 View Figures 5–9 ). The prostrate part extends into short upright threads, with rounded or bottle-shaped terminal sporangia barely larger than the vegetative cells (Fig. 8 View Figures 5–9 ). The branches are predominantly unilateral, with pseudo-binary branches and the cell wall of the branch is separated from the main axis cell (Fig. 9 View Figures 5–9 ). Cells of upright threads are irregularly cylindrical or subcylindrical and not constricted or slightly constricted. Cells are 4–7 μm wide, with a length 2–8 times longer than width. The parietal chloroplast contains 1–2 protruding pyrenoids or 3 in some dividing cells (Figs 18–21 View Figures 18–27 ).

Biflagellate zoospores were formed within terminal sporangia (Fig. 10 View Figures 10–17 ). Asexual reproduction produces two-flagellated zoospores which are usually elliptic, about 4 × 7 μm (Fig. 11 View Figures 10–17 ). Zoospores shed flagella, elongate (Figs 12 View Figures 10–17 , 13 View Figures 10–17 ). The germination of zoospores is generally unidirectional to form a filament with two cells (Figs 14 View Figures 10–17 , 15 View Figures 10–17 ). Four-day-old culture, the intercalary cells of the young filament, one-two cells in length, begin to form lateral branches (Fig. 16 View Figures 10–17 ). The cell wall of branch is separated from the main axis cell (Fig. 17 View Figures 10–17 ). Each cell is with one parietal chloroplast (Figs 13–17 View Figures 10–17 ). At early stages of development, the size of the main axis cells and branch cells is not much different, 4–6 μm wide, length 1–2 times longer than width.

Vegetative reproduction occurs via the disintegration of the upright threads into spherical or egg-shaped cells (Figs 18–27 View Figures 18–27 ), which form two cells through binary fission (Figs 19–21 View Figures 18–27 ). The cells slowly form short filaments through elongation (Figs 22 View Figures 18–27 , 23 View Figures 18–27 ) and finally develop into a green algal colony with two parts, the prostrate part and the erect part (Figs 24–27 View Figures 18–27 ).

Ultrastructural analysis revealed that each pyrenoid is traversed by thylakoid membranes (Figs 28 View Figures 28–31 , 29 View Figures 28–31 ). Each cell has a thick, multilayered cell wall, one nucleus and no plasmodesmata between adjacent cells (Figs 30 View Figures 28–31 , 31 View Figures 28–31 ).