Nitella acanthospora 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 : 324-326

Nitella acanthospora Casanova & Karol , sp. nov.

Type: Nardoo Lake , 35 km south-east of The Granites, Tanami Desert, 16 Aug. 2001, P. K.Latz 17988 (holo: DNA!) .

Dioecious. Plants lightly calcified, with tiny, elongate homeoclemous fertile whorls ( Fig. 1 a ). Axes up to 200 μm wide; internodes upwards of 5 mm long, longer than the branchlet whorls. Fertile branchlets 6 or 7 in a whorl; whorls up to 7 mm in diameter, decreasing in diameter progressively up the axis, 1 or 2× furcate; primary segments up to 1 mm long; secondary segments 3 or 4, of which 1–3 are dactyls, up to 1 mm long, usually 1 of the segments longer and again furcate into 3 or 4 dactyls ( Fig. 1 b ). Sterile branchlets longer and more evenly furcate, up to 5 mm long, 2 or 3× furcate; primary segments 2–4 mm long; secondary segments up to 1 mm long, furcate into 1–5 segments, of which 1–3 are dactyls, the remainder up to 1 mm long and again furcate into 2–4 dactyls ( Fig. 1 d ). Dactyls up to 0.5 mm long, bicellulate; end-cell somewhat obtuse ( Fig. 1 e ), deciduous on older whorls. Heads (contracted reproductive whorls distinguished from the vegetative parts) not really formed, although the fertile branchlet whorls have consecutively shorter branchlets and are separated by long internodes. Gametangia on separate plants; oosporangia single, geminate or clustered at all furcations; antheridia single, central to the first furcation. Oosporangia up to 200–300 μm long, 250 μm wide, with 7 or 8 helical stripes, the coronula cells slightly longer in the upper row ( Fig. 1 c ). Oospores 180 – 240 μm long, 150–180 μm wide with 7 striae ( Fig. 1 k ), ornamentation densely spinose on the fossa and sometimes continuing up the flanges ( Fig. 1 i ), with 6–16 very small spines across the fossa ( Fig. 1 h–j ), sometimes in dentate rows ( Fig. 1 f ). Antheridia up to 300–400 μm in diameter. Chromosome numbers not known.

Taxonomic notes

The oospores of this species are distinctly and densely spinose, with spines sometimes continuing up the flanges on

the oospore. Nitella acanthospora was compared with other species with elongate projections on the oospore wall. Of these, Nitella sonderi has generally sparse papillae that do not continue onto the flanges; N. penicillata has similar oospores, but the vegetative morphology is very different; N. mathuatae Allen is monoecious, with spines much less pronounced, and the vegetative morphology is very different; N. haageniae Raam is monoecious and the papillae are flattened terminally and much broader, and N. knightiae J.Groves & E.L.Stephens has unicellulate dactyls and projections that are much more conical and surrounded by iteratively smaller conical projections. There is variation in oospore size and number of spines across the fossa among populations of N. acanthospora , and further material is needed to clarify the limits of species characters.

Recognition

This species is distinguished from other arid-zone species on the basis of its homeoclemous whorls and the somewhat obtuse end-cells of the dactyls. The oospores are also distinctively different from those of other small Nitella species, with which it might be confused (see images for N. heterophylla (A.Braun) A.Braun , and N. biformis A.Braun ).

Distribution

Occurring in the arid zone of the Northern Territory and New South Wales, in tanks and bores.

Etymology

From the Greek ‘ akanthos ’ (spiny) and ‘ sporus ’ (a seed or spore) in reference to the spiny oospores.

Specimens examined

NORTHERN TERRITORY: 11 km S of Newhaven Homestead, common in clear, shallow gypsum lake, 29 Apr. 2001, P. K.Latz & D. E.Albrecht 17713 (DNA); 7 km S of Sangsters Bore, Tanami Desert , saline water, 14 Aug. 2001, P. K.Latz 17985 (DNA) [a mix of two species] . NEW SOUTH WALES: Dead Horse Tank , 11 Dec. 1998, J. L.Porter 169 ( MEL) .

Figures

Fig. 1. (Caption on next page)