Nitella oollooensis Casanova & Karol 2023, sp. nov.
Creators: name: Casanova, Michelle T.
name: Karol, Kenneth G.
Publisher: name: Zenodo
Year: 2023
Subjects: Biodiversity
Taxonomy
Plantae
Charophyta
Charophyceae
Charales
Characeae
Nitella
Nitella oollooensis

description: Nitella oollooensis Casanova & Karol, sp. nov.   
 Type: Site 5, Daly River, 0.15 m deep, 6 Sep. 2010, M. T.Casanova & J.Schult r776 (holo: DNA!).   
 Dioecious. Plants small, with spreading whorls and no mucus; up to 10 cm high; with bunches of furcations at the elongate fertile branchlet tips (Fig. 13 a, b). Axes up to 350 µm wide; internodes up to 35 mm long, longer than the branchlet whorls. Fertile branchlets 6–8 in a whorl, with a central secondary segment (monopodial); primary segments up to 5–7 mm long; secondary segments 4–6, of which one is central and longer, up to 2 mm long; the shorter ones divided into 4–6 tertiary segments, up to 0.5 mm long, some of which are dactyls; the central one divided into 5–7 segments of which one is central; some again divided into 2–4 quaternary segments (dactyls) (Fig. 13 d). Sterile branchlets 6–8 in a whorl, up to 15 mm long, with longer secondary and tertiary segments than in the fertile branchlets (approximately half the total length), but also with a central percurrent segment (Fig. 13 f–h); primary segments up to 6 mm long, secondary segments 3–5, 3–5 mm long, unevenly divided into 3–5 tertiary segments, up to 1 mm long. Fertile dactyls bicellulate (Fig. 13 d); the end-cell shortly conical and acute, confluent with the end of the penultimate cell. Sterile dactyls similar to fertile but often longer. Heads not formed; however, the fertile whorls are often well separated along the upper axes. Gametangia on separate plants, antheridia single and central at the final furcations (Fig. 13 e), oosporangia single and lateral to the 2 upper-most fertile branchlet nodes (Fig. 13 c). Oosporangia up to 400 µm long × 300 µm wide with ~8 helical stripes; coronula up to 20 µm high, the upper cells as long as the lower cells. Oospores 230–240 µm long × 200–230 µm wide with 7 or 8 flanges ~8 µm high (Fig. 13 i), the ornamentation of interlocking sinuous verrucae (Fig. 13 j), becoming linear onto the flanges. Antheridia up to 200 µm in diameter (Fig. 13 e). Chromosome numbers not known.   Taxonomic notes  
 This species would have been designated a form of Nitella pseudoflabellata var. imperialis ( ≡ N. imperialis ) in the past because of the central percurrent ray. However, N. imperialis differs in having an oospore with a fibrous construction. The central percurrent rays are reminiscent of N. monopodiata Raam from Tasmania; however, that species is monoecious, rather than dioecious. The presence of ‘little brushes’ of furcations at the branchlet tips is reminiscent of the description of N. robertsonii A.Braun by Nordstedt (1883), but the oospores are quite different.   Recognition  
 The central rays and the spreading fertile branchlets with elongate primary segments are distinctive. In Nitella nitida, there are elongate primary segments on the fertile whorls; however, there is no central ray, and the branchlets are less furcate.   Distribution  
In streams and rivers in the Douglas– Daly region of the Northern Territory.  Etymology  
This species is named for the location of its habitat (Oolloo Crossing on the Daly River) and for the Oolloo aquifer that keeps the river flowing perennially.  Specimens examined  
 NORTHERN TERRITORY: Oolloo Crossing, Daly River, 0.15 m deep, 6 Sep. 2010,  M. T. Casanova & J. Schult r767 (DNA, MEL) r770 (MEL), r772 (DNA, MEL); Fish River station, near northern creek, 0.2 m depth, 26 Apr. 2012,  I. D.Cowie 13207 (DNA 215653); Middle Creek, Douglas–Daly region, 0.25 m depth, 6 Sep. 2010, M. T. Casanova r763 (MEL)  .
description: Published as part of Casanova, Michelle T. & Karol, Kenneth G., 2023, Charophytes of Australia's Northern Territory - II. Tribe Nitelleae, pp. 322-353 in Australian Systematic Botany 36 (4) on pages 343-345, DOI: 10.1071/SB22029, http://zenodo.org/record/10904369