Chara arnhemensis (R.D.Wood) 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 : 49-51

Chara arnhemensis (R.D.Wood) Casanova & Karol , comb. nov., stat. nov.

Chara fibrosa f. arnhemensis R.D.Wood, Taxon 11: 13 (1962). Type: NORTHERN TERRITORY, Hemple Bay, Groote Eylandt, at edge of freshwater lagoon, 7 May 1948, R. L. Specht A21 (holo: AD!; iso: L!, MEL!, NY!).

‘ Chara spechtii’: R.D.Wood herb., ined.

‘ Chara sp. nov.?’: R.D. Wood, Rec. American–Australian exped. Arnhem Land 3: 137 (1958).

Chara arnhemensis R.D.Wood, Rev. Characeae 1: 770 (1965), nom. inval., nom. alt.

Monoecious. Plants up to 35–150 mm high, with short compact upper internodes in shallow water, and with so many long accessories as to appear prickly, without calcification ( Fig. 6 a, c ). Axes filiform, 100–300 μm wide, internodes 6–12 mm long, essentially 2× corticated, ~16 cells around, anisostichous (i.e. cell sizes variable; Fig. 6 d ), cortex appearing 1× near the nodes, and rarely appearing 3× in the centre of the internode where upper and lower secondary cells might intermingle. Spine cells abundant, occurring singly, up to 1 mm long and 50–80 μm in diameter, acute, spreading and appressed ( Fig. 6 f ). Stipulodes up to 2.5 mm long and 50–80 µm wide, in a single whorl, 2 per branchlet, acute ( Fig. 6 b ). Branchlets ecorticate, 8–9 in a whorl, 3–5 mm long, 250 μm wide, with 3 or 4 segments, a bunch of bract cells at the apices, basal branchlet cell much shorter than the stipulodes, similar in length to the other branchlet cells ( Fig. 6 g ). Bract cells up to 1.4 mm long, verticillate, 3–6 of them ( Fig. 6 e ). Bracteoles 2, shorter than the bract cells, up to 1.0 mm long. Gametangia conjoined singly at the lowest branchlet node, occasionally at a second node ( Fig. 6 b, e ). Oosporangia 245–300 μm long, 195–250 μm wide, 6 stipes of helical cells, coronula up to 50 µm high, 200 µm wide, cells spreading. Oospores tiny and black, broadly oval, somewhat flanged, 210–250 µm long, 180–210 µm wide with 6–8 striae ( Fig. 6 h ), oospore wall smoothly flocculate, appearing felted and porate at very high magnification ( Fig. 6 i ), fossa up to 60 µm across. Antheridia 150–200 µm in diameter. Chromosomes not known.

Distribution

This species is apparently restricted to freshwaters on Groote Eylandt in the Gulf of Carpentaria.

Etymology

The type material was collected on the 1948 American– Australian expedition to Arnhem Land and the species is named for the area in which the expedition was undertaken. Notes

This species is distinctive, mostly in relation to the elongate stipulodes, bract cells and long and abundant spine cells. This is the smallest species of Chara in the Northern Territory, with the smallest oospores of any known species of Chara ( Wood 1959) .

This species was called ʻ Chara spechtii ’ as a manuscript name, although Wood (1962) chose to publish it as Chara fibrosa subsp. fibrosa f. arnhemensis .

Specimens examined

NORTHERN TERRITORY: Little Lagoon, Groote Eylandt , in a freshwater swamp, 18 May 1948, R. L. Specht A29 ( AD, NY) .

Figures

Fig. 6. Chara arnhemensis from the isotype specimen R.Specht A21 (MEL). (a) Axis and branchlets of whole shoot, scale bar: 10 mm. (b) Section of axis with fertile branchlet whorl, scale bar: 1 mm. (c) Apex of a shoot, scale bar: 1 mm. (d) Transverse section of axis, scale bar: 100 µm. (e) Fertile branchlet with oogonia, antheridia, bracteoles and bract cells, scale bar: 1 mm. (f) Longitudinal view of axis with 2× cortication and long spine cells, scale bar: 1 mm. (g) Whorl of branchlets viewed from above, showing gametangia at the first branchlet nodes, scale bar: 1 mm. (h) Scanning electron micrograph (SEM) of whole oospore with 7 or 8 striae (damaged during preparation), scale bar: 50 µm. (i) SEM of felted, porate fossa wall, scale bar: 2 µm.