Chara barbata Meyen, Linnaea 2: 75 (1827); Nitella barbata (Meyen) Rabenh., Deutschl. Krypt. -Fl. 2(2): 196 (1847). Type: In lacu ‘ Plötzensee ’ vicinia Berol. locus classic., 1828, Bennett (neo: NY! 01089212, fide R.D.Wood in R.D.Wood & K.Imahori (eds), Rev. Characeae 1: 347 (1965) [illustrated as ICON 167 by K.Imahori]).

Monoecious. Plants from 10 cm up to 1.2 m high, with a shrubby growth habit in shallow water (Fig. 1 a), but with elongate stems in deeper, flowing water, occasionally with calcium carbonate deposition on the thallus. Axes up to 600 µm in diameter, the cortex reduced to whiskers of filaments below the stipulodes (Fig. 1 c). Spine cells absent or inconspicuous on longer cortical filaments. Stipulodes in one whorl, 2× the number of branchlets, uniform in length in each whorl, but variable on a single plant (Fig. 1 c). Branchlets 8–9 in a whorl, up to 30 mm long, 3–5 segments long, uncorticated, terminated by an acuminate end cell (Fig. 1 b). Bract cells 4–6, verticillate and elongate (up to 12 mm long) at the branchlet nodes (Fig. 1 d), bracteoles shorter than bract cells, occurring below the gametangia. Gametangia arranged side-by-side at the lowest 1–2 branchlet nodes, arising from separate gametangial initials (Fig. 1 e). Oosporangia 700–1100 µm long and 500–800 µm wide, with 10–12 stripes of helical cells, coronula up to 100 µm high (Fig. 1 e). Oospores brown to black, 700–790 µm long, 450–490 µm wide (Fig. 1 g), often with a gyrogonite 800–960 µm long (Fig. 1 f) (García 2003). Striae of 9–11 strong ridges, fossa wall minutely verrucate (Fig. 1 h). Antheridia up to 350 µm in diameter, 8-scutate (Fig. 1 g). Chromosomes n = 28 (Hotchkiss 1963).

Occurs in freshwater, permanent lakes and ponds in Europe, North America, Asia, Papua New Guinea, Timor-Leste, and tropical and subtropical Australia. In Australia, specimens have been recorded in freshwater streams and rivers. Fossil records (gyrogonites) from the Holocene occur in Europe, Australia, Asia, North America and Africa (Casanova et al. 2003 a; García and Chivas 2006; Sugier et al. 2009; Vicente et al. 2020). The species is included here on the basis of reports from García and Chivas (2006) from the Gulf country in far-northern Queensland (n.v.), its occurrence in PNG (Leach and Osborne 1985; n.v.), and the examination of a specimen from Timor-Leste (D.Cook & T.Lee s.n. (DNA)).

In Europe, Lychnothamnus barbatus occurs usually in temperate lakes, often associated with Nitellopsis obtusa (Desv.) J.Groves (Brzozowski et al. 2021). In Australia, it has been found in deep pools and riffles in freshwater creeks subject to variable flow (0.5–1.5 m deep), and its germination was enhanced in experiments by drying the sediment (Casanova et al. 2003 b).

Lychnothamnus barbatus is likely to be a perennial species where its habitat is perennial. Australian specimens have been robust and well developed; however, it has been collected only in spring and summer, so its life-history requirements are not known. Reproductive organs and oospores have been found in summer. Oospore germination occurred in soil samples dried over winter and flooded in November (spring) (Casanova et al. 2003 b).

This species has been listed as ‘Endangered’ in Australia under the Commonwealth Environment Protection and Biodiversity Conservation Act 1999 and the Queensland Nature Conservation Act 1992 (McCourt et al. 1999; Casanova et al. 2003 b). It has also been Red-Listed as endangered or critically endangered in Poland (Siemińska et al. 2006), Lithuania (Balevičius 2000), Germany (Ludwig et al. 1996; Korsch et al. 2013) and the Balkans (Blaženčić et al. 2006).

Barbatus meaning ‘bearded’ in Latin. Named for the whiskers of cortical cells that emerge from the axial nodes.

Lychnothamnus is the only genus (world-wide) with gametangia regularly arranged side-by-side. Sterile specimens of L. barbatus can be distinguished from species of Chara by the incomplete axial cortex and ecorticate branchlets, from Australian species of Lamprothamnium by the incomplete axial cortex and the characteristic bract cells, and from robust species of Nitella by the presence of stipulodes, cortication and monopodial branchlets. Indian material (in BM) is more completely corticated than is Lychnothamnus from other places, with primary cortical cells sometimes fully developed, along with spine cells. Lychnothamnus has not yet been recorded from the Northern Territory, but is likely to occur there in suitable habitat. The Australian material differs genetically from material from Europe (McCourt et al. 1999), but the differences are not sufficient for it to be recognised as a different species.

QUEENSLAND: Warrill Creek near Aratula, 21 Nov. 1960, R.D.Wood 60-11-21-3 (BM, CANB, L, PC); Wallace Creek at the end of C. Head Road, off the Boonah-Rathdowney Road, in deep pools shaded by Casuarina and Callistemon, 15 Dec. 1996, M. T.Casanova v536 (MEL, NE, NY); Wallaby Creek on the D’Anguilar Highway M. T.Casanova x098 (MEL, BRI, NY). TIMOR-LESTE: Lake Iralalaro–Irasequiro area, 2 Oct. 2009, D.Cook & T.Lee s.n. (DNA). INDIA: Gondah, Oudh, 9 Feb. 1923, G. O.Allen 32 (BM). GERMANY: Obersee bei Lanke, Berlin, 23 June 1872, P.Magnus (BREM); Auf überschwemmerten Moorgrund zwischen Schöneburg u. Willmersdorf bei Berlin, August 1829?, F.Bauer (BREM); Schoneberg, Aug. 1829, F.Bauer (BM).