Chnoospora implexa J.Agardh
Spec.Gen.Ord.Alg. 1:172 (1848)

Conservation Code: Not threatened
Naturalised Status: Native to Western Australia
Name Status: Current


Beard’s Provinces: Eremaean Province.

IBRA Regions: Pilbara.

IBRA Subregions: Roebourne.

IMCRA Regions: Pilbara (nearshore).

Local Government Areas (LGAs): Karratha.

Scientific Description
John Huisman & Cheryl Parker, Thursday 8 September 2016

Habit and structure. Thalli consisting of densely aggregated interconnected dichotomous axes anchored to rock and coral rubble by numerous fibrous holdfasts composed of dense aggregates of free undivided filaments derived from cortical cells mostly at the apices of dichotomous axes. Under moderate water-movement conditions large numbers of erect axes forming a cushion-like configuration, these producing widely spaced (to 12 mm apart) dichotomies and subdichotomies below and more densely crowded forks above. Fronds very pale to very dark brown, the former usually displaying a characteristic farinaceous texture, 3–9 cm long, growing from broadly rounded tips 200–400 µm wide, with tufts of anchoring fibres commonly arising from the tips or laterally. Cortical cells cuboidal to rectilinear in surface view, in concentrically arching rows. Axes initially terete but becoming progressively oval or compressed, proximally to 1500 µm long and 400–900 µm wide. Cortical cells containing a single plastid with a circular pyrenoid. Axes parenchymatous throughout, the medulla composed of colourless thin-walled cells to 500 µm long and 90–250 µm in diameter. Large central medullary cells grading through smaller cells to the single-layered cortex of cuboidal to rectilinear cells 20–90 µm long, 10–20 µm wide and c. 10 µm tall. Most fronds with scattered shallow pits from which trichothallic hairs emerge.

Reproduction. Fertile thalli, collected in May and December, with the plurangial sori forming irregularly contoured and usually transversely aligned patches to 260 µm long and 350 µm wide, beginning within 1 mm of the apex. Sori covered by a cuticle that splits with expansion of the sporangia leaving a remnant around mature structures. Remnants of broken cuticles on developing sori visible as thin flaps on which impressions of the underlying cortical cells are embossed. Plurangial organs binate or quadrate in surface view, uniseriate or biseriate in lateral view and 20–25 µm long and 7–8 µm wide. Once the plurangial contents have been shed, the space previously occupied by the organ remains as a deep cavity in the frond surface.

Distribution. This species is found in most tropical seas, but it is predominantly reported from the IndoPacific. In Australia, it is known from mainland Qld., the Great Barrier Reef and Lord Howe I.

[After Kraft, Algae of Australia: Marine Benthic Algae of Lord Howe Island and the Southern Great Barrier Reef, 2: Brown Algae: 108–112 (2009)]