Nitella limosa Casanova & Karol, 2023

Casanova, Michelle T. & Karol, Kenneth G., 2023, Charophytes of Australia’s Northern Territory - II. Tribe Nitelleae, Australian Systematic Botany 36 (4), pp. 322-353 : 337

Nitella limosa Casanova & Karol , sp. nov.

Type: Girraween Lagoon near Darwin, 3 Sep. 2010, M. T. Casanova & J . Schult r738 (holo: DNA!; iso: MEL!, NY!) .

Dioecious. Plants 15–40 cm high; elongate, diffuse and flexible with mucus-covered fertile parts ( Fig. 8 a ). Axes up to 450 µm wide; internodes up to 60 mm long, but usually less than 40 mm, longer than the sterile branchlets when growing in deep water. Fertile branchlets 6 in a whorl; 3 to rarely 4× furcate; primary segments up to 5 mm long; secondary segments 4 or 5, to 0.5–1 mm long; tertiary segments 3–5, 0.2–0.5 mm long; quaternary segments (= dactyls) 2–4, 2 cells long, both cells elongate, each up to 500 μm long, the end-cell apex obtuse ( Fig. 8 c ); sterile branchlets 6 in a whorl; 3× furcate; primary segments up to 2 cm long; secondary segments 6–8, up to 4 mm long; tertiary segments 4–6, up to 3 mm long, again furcate into 3–5 dactyls ( Fig. 8 b ), up to 5 mm long, made up of 2 or 3 cells; end-cells elongate and obtuse. Fertile branchlets somewhat contracted, but the fertile branchlet primary segments remain elongate, and the remaining segments are contracted into tufts: mucus present and sometimes abundant. Gametangia occurring singly at the 2nd and 3rd fertile branchlet nodes. Oosporangia solitary at nodes, up to 450 µm long with ~7 helical stripes; coronula up to 30 µm high, cells equal sized ( Fig. 8 c ). Oospores up to 350–400 µm long × 280–320 µm wide with 9 or 10 flanged striae ( Fig. 8 d ); the flanges up to 20 µm high; ornamentation reticulate, a network of 10–15 shallow holes across the fossa, the edges of the holes sometimes well defined (~1 µm wide), ornamentation continues up the flanges for at least 10 µm ( Fig. 8 e ). Basal-cell impressions 50 µm wide at the widest part, the larger cell pentagonal, the smaller cell rectangular ( Fig. 8 f ). Antheridia up to 300 µm in diameter. Chromosome numbers not known.

Recognition

This species was originally determined as Nitella myriotricha ( Wood 1971) because of the pluricellulate branchlets, dioecy and abundant mucus, but examination of the

oospores using SEM showed a much larger and more reticulate oospore. This species has 3× furcate branchlets, and the distal fertile segments on very long primary segments, so that the appearance of fertile parts in the water is of glistening orange stars.

Distribution

Lagoons and wetlands in the wet tropics of the Northern Territory.

Etymology

From the Latin limosus (slimy); although this word has negative connotations in the English language, it is a field character that is very distinctive.

Specimens examined

NORTHERN TERRITORY: Yamburram Range, 15 May 1994, N. Walsh 3773 ( MEL); Lyons Lagoon near Darwin , 3 Sep. 2010, M. T. Casanova & J . Schult r748 (DNA, MEL, NY); Woodford Lagoon near Darwin , 3 Sep. 2010, M. T. Casanova & J . Schult r743 (DNA, MEL, NY); Groote Eylandt, Little Lagoon , in Gulf of Carpentaria, in freshwater swamp, 28 May 1948, R. Specht A27 ( BM, MEL, NY 02022347 ); pool on Stuart? Creek, E of Humpty Doo Road , 50 miles [~ 80.5 km] S of Darwin, 20 Apr. 1961, R.D. Wood , N. Eddy & A . Wilson 61-4-20-20 ( BM, NY 02020653 , NY 02022339 , NY 02285722 ) .

Figures

Fig. 8. Nitella limosa from holotype specimen M.T.Casanova & J.Schult r738 (DNA). (a) Habit of whole plant, scale: 1 cm. (b) Sterile whorl, scale: 10 mm. (c) Female fertile branchlet, scale: 500 µm. (d) Scanning Electron Microscope (SEM) image of oospore, scale: 200 µm. (e) SEM image of detail of oospore wall, scale: 20 µm. (f) SEM image of impression of end-cells on oospore wall, scale: 100 µm.