Chara duriuscula (A.Braun) Casanova & Karol, 2023

Casanova, Michelle T. & Karol, Kenneth G., 2023, Charophytes of Australia’s Northern Territory - I. Tribe Chareae, Australian Systematic Botany 36 (1), pp. 38-79 : 55-57

Chara duriuscula (A.Braun) Casanova & Karol , comb. nov., stat. nov.

Chara gymnopitys var. duriuscula A.Braun in C. F. O.Nordstedt, Abh. Königl. Akad. Wiss. Berlin 1882: 126 (1883); Chara fibrosa subsp. gymnopitys var. duriuscula (A.Braun) Zaneveld , Blumea 4: 160 (1940). Type: NORTHERN TERRITORY: Victoria River, May 1856, F. v. Mueller 2 (holo: LD!).

[ Chara fibrosa var. fibrosa auct. non C.Agardh ex Bruzelius: R.D.Wood, Nova Hedwigia 22: 26 (1971).]

Monoecious. Plants up to 120 mm high, with long branchlets in the basal whorls, upper whorls slightly condensed, lightly to heavily calcified ( Fig. 10 a ). Axes up to 550 µm in diameter, 2–partly 3× corticated, secondary cells (and tertiary cells where present) smaller than the primary (tylacanthous), ~16 cells around ( Fig. 10 c ). Internodes 5–20 mm long. Spine cells solitary, very small but acute, up to 200 µm long, only obvious on the upper, young internodes ( Fig. 10 g ), stipulodes in 1 row, narrow, variable in number and length, mostly 1× the number of branchlets on the adjacent whorl, usually sticking out perpendicular to the axis, 0.4–1.2 mm long ( Fig. 10 e ). Branchlets ~ 8 in a whorl ( Fig. 10 f ), ecorticate, 4 or 5 cells long, spreading, basal branchlet cell 2.5–3.5 mm long, next two segments equally long (sometimes longer), branchlet end segments very short, exceeded by the subtending bract cells ( Fig. 10 b ), bract cells 1 or 2, internally up to 1 mm long, externally short, up to 0.8 mm long. Bracteoles 2, at least 2× longer than the oosporangium ( Fig. 10 d ). Gametangia conjoined on 2 or 3 branchlet nodes, solitary. Oosporangia to 560–590 µm long, coronula cells appressed. Oospores black, (measured dry) 380–415 µm long, 240– 290 µm wide, with 9 or 10 striae of flanged ridges ( Fig. 10 i ), the oospore wall smooth to densely papillate, papillae ~1 μm in diameter, 13–15 across the fossa ( Fig. 10 j ), basal cell impression up to 52 µm in diameter ( Fig. 10 k ). There is evidence of some deposition of calcium carbonate on the surface of oospores ( Fig. 10 h ) and thallus (although no development of a gyrogonite). Antheridia 390–440 µm in diameter. Chromosomes not known.

Distribution

Tropical rivers in the Northern Territory, possibly in Indonesia.

Etymology

From Latin: duriusculus meaning ‘somewhat hard’ perhaps referencing the somewhat calcified nature of the plant.

Notes

When collected, specimens were easily distinguished as a separate taxon (initially tentatively allocated to ʻ C. sp. aff. thwaitesii ʼ), and examination of the type material (in LD) allowed allocation of the correct name. This species differs from C. thwaitesii A.Braun by having gametangia conjoined at all branchlet nodes (rather than sejoined and occasionally basal in C. thwaitesii ; Wood and Imahori 1965).

The type specimen was designated a variety of C. gymnopitys A.Braun in Nordstedt (1883), distinguished on the basis of oospore size and number of branchlets. Zaneveld (1940) retained it as a variety of C. fibrosa subsp. gymnopitys , occurring in Australia, but not the Malay peninsula. Groves and Allen (1935), Wood (1962), and Wood and Imahori (1965) made no mention of this taxon. Wood (1971) amalgamated it with C. fibrosa f. fibrosa , mentioning it only in synonymy.

Chara duriuscula is a somewhat smooth-looking monoecious charophyte with black oospores, corticated axes and naked branchlets. It has inconspicuous spine cells and few bract cells (mostly internal to the branchlets), and all branchlet segments are long. It differs from C. benthamii (with which it has an overlapping distribution) by having granulate ornamentation on the oospores, more cortical cells, fewer bract cells and gametangia confined to the bottom nodes of the branchlets. It differs from C. drummondii A.Braun by having well-developed stipulodes. It differs from C. gymnopitys in having fewer bract cells and spine cells and smaller oospores. Chara duriuscula is usually well calcified, and sometimes grows semi-emergent along the banks of tropical rivers ( Casanova and Nairn 2015).

Specimens examined

Specimens: NORTHERN TERRITORY: Oolloo Crossing, Daly River , 6 Sep. 2010, M. T . Casanova r765 ( BM, DNA, MEL, NY), r766 ( MEL) r771 (DNA, MEL, NY); Daly River, Camp site 5, 6 Sep.2010, M. T . Casanova r773 ( MEL), r774 (DNA, MEL, NY), r780, r781 ( MEL); Barnes Creek , Arnhemland,1854, F. v. Mueller s.n. ( MEL); Arnhemland, Wilton River , 10 Nov.1987, G. Leach 1662 & C . Dunlop (DNA) [mixed with C. lucida ]; Bullo River Station , spring-fed stream, 9 Mar. 2006, D. J. Dixon 1558 (DNA, NSW) .

Figures

Fig. 10. Chara duriuscula, (a, d, f) from M.T.Casanova r773 (MEL), (b, i–k) from the holotype specimen F. v. Mueller 2 (LD), (c, g–h) from M.T.Casanova r781 (MEL), (e) from M.T.Casanova r774. (a) Habit of whole plant, scale bar: 10 mm. (b) Fertile branchlet whorl, scale bar: 1 mm. (c) Transverse section of axis, scale bar: 200 µm. (d) Fertile node with oosporangium, antheridium, bracteoles and bract cells, scale bar: 1 mm. (e) Whorl of stipulodes below the branchlets, scale bar: 1 mm. (f) Whorl of fertile branchlets, scale bar: 5 mm. (g) Young axis with spine cells. (h) Light micrograph of an oospore with evidence of calcification, ~500× magnification. (i) Scanning electron micrograph (SEM) of oospore with nine striae and a granulate fossa wall, scale bar: 100 µm. (j) SEM of oospore wall, scale bar: 20 µm. (k) SEM of pentagonal basal cell, scale bar: 50 µm.