Nitella martinii Casanova & Karol 2023, sp. nov.

Nitella martinii Casanova & Karol, sp. nov.

Type: Roadside Borrow Pit on the Arnhem Hwy, 8 Sep. 2010, M. T.Casanova r785. (holo: DNA!, iso: BM!, MEL!, NY!).

Dioecious. Plants up to at least 30 cm high; branchlets up to 3× furcate; all branchlet segments long, spreading and diffuse, without mucus (Fig. 9 a). Axes up to 400 µm wide; internodes up to ~ 60 mm long in most parts, some exceptionally long (15 cm). Fertile branchlets 6 in a whorl, ranging from shorter and less furcate than the sterile whorls to approximately the same (Fig. 9 c); primary segments up to 6 mm long; secondary segments 4 or 5, 3–7 mm long, divided at the tips to 2 or 3 brachydactylous tertiary segments, up to 0.5 mm long; sterile branchlets 6 or 7 in a whorl; up to 25 mm long, with longer segments than fertile branchlets, 3(–4)×furcate (Fig. 9 b); primary segments up to 12 mm long, secondary segments ~5, of which one is central, 7–13 mm long; the shorter ones divided into 2 or 3 tertiary segments, 5–13 mm long, some of these are dactyls and 1 or 2 of them again divided into 2 or 3 dactyls. Fertile dactyls 2 or 3, bicellulate, the end-cell shortly conical and acute, somewhat bristle-tipped, some very long (5–7 mm) others very short and brachydactylous (Fig. 9 f). In some cases, the final branchlet segments in fertile whorls appear to be stipes for gametangia. Sterile dactyls similar to fertile but longer. Some shoots appear to be specialised vegetative reproductive organs (turions), with contracted, starch-filled whorls of branchlets (the starch in the primary branchlet segments, and all other segments reduced). Heads not formed. Gametangia on separate plants, antheridia single and geminate at final 2 furcations, often appearing to be terminal to the entire branchlet (Fig. 9 d), oosporangia single, geminate and clustered lateral to most of the fertile branchlet nodes (Fig. 9 c). Oosporangia up to 500 µm long, 350 µm wide with 6 or 7 helical stripes; coronula up to 30 µm high, the upper cells as long as the lower cells (Fig. 9 e). Oospores 400–450 µm long × 350–400 µm wide with ~8 flanges ~20 µm high united in a crest at the apex of the oospore (Fig. 9 g); the ornamentation appears lowly verrucate, and dry oospores are pale, spongy brown (Fig. 9 h). Basal-cell impression apparently single, rectangular (Fig. 9 i). Antheridia up to 300 µm in diameter. Chromosome numbers not known.

Only one gathering has been made, but this species is so distinctive that it warrants description.

In the only gathering, Nitella martinii formed wiry masses of clear green shoots in shallow water. The diffuse and spreading habit could be confused with Chara lucida (A.Braun) Casanova & Karol, with which it was growing, but the stems were more wiry. The absence of mucus and dispersed fertile branchlets are distinctive.

Only one locality is known, which is likely an ephemeral one (roadside borrow-pit) on the Arnhem Highway. It is likely to be more widely distributed in temporary wetlands in the Northern Territory.

This species is named in honour of Martin O’Brien, who worked with the Victorian Scientific Advisory Committee for many years, providing information and expertise in relation to the conservation and listing of endangered species, communities and potential threatening processes.

Known only from the type material.