Nitella crocodylus 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 : 333-335

Nitella crocodylus Casanova & Karol , sp. nov.

Type: Manton Dam, 5 Sep. 2010, M. T.Casanova r760 (holo: DNA!; iso: BM!, MEL!, NY!).

[ Nitella pseudoflabellata f. sonderi auct. non ( A.Braun) R.D. Wood : R.D. Wood in R.D. Wood & K.Imahori, Revis. Charac. 1: 589–590 (1965)].

[ Nitella pseudoflabellata var. imperialis auct. non T. F.Allen: R.D. Wood , Nova Hedwigia 22: 69 (1971)].

Dioecious. Plants up to 30 cm high, with some long branchlets along the axis; plant apex with mucus-covered heads ( Fig. 6 a, c ). Axes 400–500 µm wide; internodes up to 12 cm long in the lower parts, 10–20 mm in the upper parts, approximately as long as the sterile branchlets. Fertile branchlets 6 in a whorl; variable in length, some very short and in contracted whorls, others with very long (6–9 mm) primary branchlet segments; mostly 2× furcate, primary segments 1–9 mm long, secondary segments 4–6, up to 0.5–2 mm long or more if not bearing gametangia, 3–6 tertiary segments (dactyls) up to 0.6 mm long. Sterile branchlets 6 in a whorl, 2× furcate, primary segments 5–15 mm long, secondary segments 3–5, up to 6 mm long but often shorter, tertiary segments (dactyls) 2 or 3, up to 3 mm long ( Fig. 6 b ). Fertile and sterile dactyls similar, bicellulate, up to 1 mm long, tapering to a conical, acute end-cell ( Fig. 6 d ). Fertile branchlets often contracted into axial and apical heads ( Fig. 6 c ). Post-fertile branchlets apparently extend the primary branchlet segment, appearing as little brushes of segments and dactyls at the tips ( Fig. 6 e ), mucus present around young fertile branchlets. Gametangia on separate plants at all fertile branchlet nodes. Oosporangia solitary, coronula up to 20 µm high, upper cells approximately the same as lower ( Fig. 7 f ). Oospores dark brown, 270–300 µm long and 240–270 µm wide ( Fig. 6 h ) with 6 or 7 striae with porous flanges 5–19 μm high and ornamentation in 2 layers; the lower layer perforate with sinuate holes ( Fig. 6 g ), the upper layer incompletely reticulate, consisting of ropey lines ( Fig. 6 i ). Basal-cell impressions almost rectangular ( Fig. 6 j ). Antheridia up to 250 µm in diameter. Chromosome numbers not known.

Recognition

This species is characterised by abundant mucus and branchlets with very long primary segments (most likely postreproductive whorls), as well as other, more regularly furcate branchlets. It is distinguished from Nitella oollooensis by the presence in N. oollooensis of central secondary and tertiary branchlet-segment lengths. The oospores are also distinctive.

Distribution

Water bodies in the vicinity of Darwin.

Etymology

This species is in reference to the animal with which the plant coexists in its habitats in the Northern Territory (Crocodylus porosus, the saltwater crocodile). It is a noun in apposition.

Specimens examined

NORTHERN TERRITORY: Manton Dam, 5 Sep. 2010, M. T. Casanova r761 (DNA, MEL); Yirrkala , 19 Aug. 1948, R. L. Specht A48 ( BM, NY); Angularli Creek, Murgenella , 29 Aug. 1987, G. Leach 1397 (DNA, NT) .

Figures

Fig. 6. Nitella crocodylus from isotype specimen Casanova r760 (MEL). (a) Habit of oosporangial plant, scale: 10 mm. (b) Sterile branchlet tip and dactyls, scale: 1 mm. (c) Habit of male plant, scale: 10 mm. (d) Female fertile branchlet whorl, scale: 1 mm. (e) Male branchlet whorl, scale: 5 mm. (f) Fertile female branchlet tip, scale: 1 mm (g) Scanning electron microscope (SEM) image of detail of the oospore ornamentation, a raised reticulum on a sinuously porate ground, scale: 2 µm. (h) SEM image of oospore in side view, scale: 100 µm. (i) Detail of oospore wall, scale: 20 µm. (j) View of the basal-cell impressions, scale: 50 µm.

Fig. 7. Nitella heterophylla. (a–c) From specimen M.T.Casanova r460 (MEL). (d–i) From specimen M.T.Casanova p770 (PERTH). (a) Whole plant, scale: 1 cm. (b) Whorl of branchlets, scale: 1 mm. (c) Fertilised oogonium, scale: 200 µm. (d) Fertile female shoot, scale: 1 mm. (e) Fertile male shoot, scale: 1 mm. (f) Chromosomes in metaphase, 1000× magnification. (g) Scanning electron microscope (SEM) image of oospore in side view, scale: 100 µm. (h) SEM image of detail of oospore wall, scale: 20 µm. (i) SEM image of basal view of oospore, showing end-cell impressions on the oospore wall, scale: 100 µm.