Canistrocarpus cervicornis (Kütz.) De Paula & De Clerck

Scientific Description

Habit and structure. Thalli epilithic or epiphytic, olivaceous to medium brown or dark brown, some drying almost black, 2–11 cm long; axes to 3 mm wide, tending to be ± uniform in each plant; branching primarily dichotomous, occasionally locally pseudomonopodial or dichotomous, the angles of forking usually 40–50°, occasionally to 120° or greater, the broadest angles usually producing at least some recurved branches; dichotomies rather evenly spaced, not concentrated distally; interdichotomies rather uniform, (2–)4–9(–25) mm long. Margins smooth, straight or sinuous, mostly without proliferations, but some thalli with patches of marginal rhizoids almost to the apices, short spines to 300 µm long or proliferations of adventitious axes to 650 µm long arising 50–500 µm in from the margin. Axes densely matted below and attached by tangles of septate branched rhizoids 10–25 µm in diameter. Hair sori distally in centred rows or scattered, oval to more elongate, 120–150 mm long, 100–120 µm wide; hairs usually remaining short and densely bundled before abscission. Apices either tapered to protuberant apical cells, occasionally abruptly (usually narrowing from 350 to 70 µm in diameter in 150 µm), or broadly rounded with protuberant or ± flush apical cells; transverse gaps between blocks of cortical cells usually prominent. Blades in medial cross-section 150–210 µm thick centrally, tending to narrow progressively toward the margins to 70–100 µm. Cortex and medulla 1-layered throughout, occasionally gaps between medullary cells filling with subcortical cells. Cortical cells 15–25 µm tall, more globular at the frond edges (to 30 µm in diameter), 15–45(–65) µm long and 10–20 µm wide, the outlines square, rectangular or trapezoidal, the cells mostly longitudinally aligned but locally non-aligned, some perpendicular to the long axis of the frond. Medullary cells 100–400 µm long, 80–190 µm wide, rectangular to polygonal, most longitudinally aligned, some wider than broad; refractive medullary cell wall thickenings absent; opaque cell inclusions 30–70 µm long and wide in medullary cells, occasionally visible through the surface as series of transverse or irregularly aligned dots.

Reproduction. Reproductive structures not seen.

Distribution. A pantropical alga that is ± equally common in both hemispheres.

[After Kraft, Algae of Australia: Marine Benthic Algae of Lord Howe Island and the Southern Great Barrier Reef, 2: Brown Algae:152–154 (2009)]