Polycerea nigrescens (Kütz.) Kylin

Scientific Description

Habit and structure. Thallus medium to dark brown, firm, slightly mucoid, usually much branched with a main axis and long laterals, occasionally with shorter, slender laterals, cylindrical, 10–40 cm long and 1–2 mm in diameter, epiphytic on Posidonia or Amphibolis. Basal system of juvenile plants consisting of a prostrate system of radiating pseudoparenchymatous filaments, from which the erect medullary filaments develop. Medulla multiaxial, firm but soon becoming hollow, of parallel, cylindrical, longitudinal filaments 20–60 µm in diameter with cells L/B2–4(–10), with slight development of hyphae. Subcortex slight to absent, rarely more than one cell long, cells 4–10 µm in diameter and L/B(1–)1.5–2.5. Cortical filaments arising directly from outer medullary cells or in small groups from the subcortical cells, forming a dense layer with filaments 100–200 µm and 6–9 cells long, 8–10(–12) µm in diameter and L/B 2–3 below, slightly larger above and terminated by a large, subglobose cell 30–60 µm in diameter and (2–)2.5–5 times the diameter of the subterminal cell. Phaeoplasts several per cell, discoid, each with a pyrenoid; physodes scattered. Phaeophycean hairs frequent, arising from outer subcortical cells, 16–25(–30) µm in diameter.

Reproduction. Plurilocular sporangia borne on pedicels 4–7 cells long from subcortical cells, simple or occasionally furcate, lanceolate, becoming multiseriate, (40–)60–100 µm long and 12–20 µm in diameter. Unilocular sporangia rare, on plants without plurilocular sporangia, formed laterally at base of cortical filaments, ovoid, 60–80 µm long and 25–35 µm in diameter.

Distribution. From Rottnest I., W. Aust., to Eden, N.S.W. and around Tas.

Habitat. Epiphytic on Posidonia, Heterozostera and Amphibolis (rarely on larger algae) in the upper sublittoral during warmer months (August to March).

[After Womersley, Mar. Benthic Fl. Southern Australia II: 124–126 (1987)]