Nitella silicea Casanova & Karol, 2023

Casanova, Michelle T. & Karol, Kenneth G., 2023, Charophytes of Australia’s Northern Territory - II. Tribe Nitelleae, Australian Systematic Botany 36 (4), pp. 322-353 : 345-348

Nitella silicea Casanova & Karol , sp. nov.

Type: Woodford Lagoon, in 0.35 m of water, 3 Sep. 2010. M. T.Casanova & J.Schult r741 (holo: DNA!; iso MEL!, NY!).

Dioecious. Plants occurring as isolated, elongate plants with flabellate whorls; up to 4×furcate ( Fig. 14 a ). Axes up to 450 µm wide; internodes up to 100 mm long. Fertile branchlets 6 in a whorl, similar to the sterile branchlets but somewhat smaller ( Fig. 14 c ); primary segments up to 10 mm long; secondary segments 6 or 7, up to 11 mm long; tertiary segments 3–5, up to 11 mm long; quaternary segments (usually dactyls) 2 or 3, up to 1 mm long, rarely further divided, 2 dactyls up to 0.5 mm long; sterile branchlets 6 in a whorl; up to 30 mm long; hardly distinguished from fertile branchlets ( Fig. 14 b ). Fertile dactyls 2 or 3; bicellulate, the end-cell shortly conical and acute, confluent with the end of the penultimate cell; dactyls of variable lengths, up to 1 mm long ( Fig. 14 d ). Sterile dactyls similar to fertile; however, where there are fewer furcations the dactyls can be up to 3 mm long. Heads not formed, the upper whorls not much contracted. Gametangia on separate plants, antheridia single and central at the final 2 furcations. Oosporangia geminate or single, lateral to the upper-most fertile branchlet nodes ( Fig. 14 d ). Oosporangia up to 400 µm long × 350 µm wide with 8 helical stripes; coronula up to 35 µm high, the upper cells longer than the lower cells ( Fig. 14 e ). Oospores 290–300 µm long × 270–290 µm wide with 7 or 8 smooth striae ( Fig. 14 f ); the ornamentation consists of closely packed, rounded verrucae, similar to cobblestones (silice) ( Fig. 14 g ). Antheridia up to 250 µm in diameter. Chromosome numbers not known.

Taxonomic notes

These specimens would have been distinguished as Nitella furcata or N. mucronata (A.Braun) Miq. by Wood (1971) because of the short dactyls; however, Wood’s concept of those species was an amalgamation of morphologically similar monoecious (and ‘submonoecious’, in the case of N. flagelliformis A.Braun ) species, including N. tumulosa Zaneveld , N. oligospira A.Braun , N. inversa Imahori , N. japonica T.F.Allen , N. axillaris A.Braun , N. axilliformis Imahori and N. orientalis , all of which are now recognised as distinct species ( Sakayama et al. 2004, 2005; Sakayama 2008). Wood (1971) found that the herbarium specimens that he called N. furcata in Australia were almost invariably sterile or poor material. Nitella silicea is dioecious rather than monoecious, and appears to be restricted to the Northern Territory

around Darwin. Other dioecious species in this group have different oospores (e.g. N. duthieae J.Groves & E.L.Stephens ).

Recognition

Nitella silicea is distinguished by its very short dactyls (terminal branchlet segments), gametangia at the distalmost furcations, a lack of mucus and distinctive oospores.

Distribution

Nitella silicea grows in shallow lagoons at the end of the wet season around Darwin, possibly more widespread, fertile in September.

Etymology

Named for the ornamentation on the oospore wall, which resembles cobblestones (for which one translation is silice in Latin).

Specimens examined

NORTHERN TERRITORY: Lyons Lagoon , 3 Sep. 2010, M. T. Casanova & J . Schult r747 ( MEL), r749 ( MEL) .

Figures

Fig. 14. Nitella silicea from isotype specimen M.T.Casanova & J.Schult r741 (MEL). (a) Habit of whole plant, scale 10 mm. (b) Sterile whorl, scale: 1 mm. (c) Female fertile banchlet, scale: 1 mm. (d) Fertile dactyls, scale: 1 mm. (e) Oogonium, scale: 100 µm. (f) Scanning electron microscope (SEM) image of oospore, scale: 100 µm. (g) SEM image of detail of oospore wall, scale: 20 µm.