Rivularia Agardh ex Bornet & Flahault (1886: 345)

Mcgregor, Glenn B., 2018, Freshwater Cyanobacteria of North-Eastern Australia: 3. Nostocales, Phytotaxa 359 (1), pp. 448-450 : 448-450

Rivularia Agardh ex Bornet & Flahault (1886: 345)

Type: R. dura Roth ex Bornet & Flahault (1886: 347)

Filamentous; filaments heteropolar, differentiated into basal and apical parts, simple, joined into firm, hemispherical or spherical, later often vast, flat, macroscopic, irregular strata, several centimetres in diameter; strata layered, with densely agglomerated trichomes oriented by their bases with heterocytes to the substratum and the apical hair-like parts towards the surface of the colony. Strata gelatinous to leathery, sometimes intensely incrusted by calcium carbonate. Trichomes generally cylindrical, constricted or unconstricted at the cross walls, dividing at intercalary heterocytes. Apical hairs composed of narrow, long, hyaline cells. Sheaths firm, sometimes lamellated, yellow-brown or colourless. Aerotopes and akinetes not produced. Cell division perpendicular to the long axis of the trichome, later in meristematic zones. Reproduction by dissociation of trichomes within colonies and heterocytes and by the production of hormogonia which are liberated following the separation of the apical hair through the production of necridic cells.

A world-wide genus with 49 species currently taxonomically accepted; most are periphytic or epiphytic. Here two species are described from north-eastern Australia; a further three species are known from elsewhere in Australia. Bibliography: Berrendero et al. (2008), Komárek (2013), Whitton & Mateo (2012), Komárek et al. (2014), León-Tejera et al. (2016), Shalygin et al. (2016).

1.

- Vegetative cells 5.0–9.8 μm long × 5.5–11.0 μm broad.................................................................................................... R. aquatica Vegetative cells 8.0–19.0 μm long × 4.8–6.5 μm broad................................................................................................ R. beccariana