Heterosiphonia callithamnium (Sond.) Falkenb.

Scientific Description

Habit and structure. Thallus medium to dark red-brown to grey-red, 1–3 cm high, with several, dense, erect axes from prostrate axes, erect axes with few lateral branches, bearing pseudolaterals distichously arranged but branched largely in transverse planes. Attachment by rhizoids; epiphytic on Amphibolis, Sargassum, Haliptilon and other algae. Structure. Apices of axes sympodially and distichously branched, developing 4 pericentral cells beginning 8–15 cells below apical cells, mature axial segments 130–180 µm in diameter and L/D 0.8–1.4. Pseudolaterals 2 axial segments apart, 1–1.5 mm long, the basal 2 segments only becoming polysiphonous, the rest monosiphonous and branched 4–5 times mostly 2 cells apart at wide angles (usually >90°), lower monosiphonous cells 60–80 µm in diameter and L/D 0.8–1.4(–2), tapering gradually to upper cells 25–40 µm in diameter and L/D 1–1.5, then to acute to mucronate terminal cells. Lateral branches probably arising on lower segments of pseudolaterals. Attachment rhizoids arising from lower cells of pseudolaterals, several cells long with multicellular haptera. Rhodoplasts discoid.

Reproduction. Gametophytes dioecious. Procarps unknown. Cystocarps sessile on a polysiphonous branch, ovoid with a short neck, 350–700 µm in diameter; pericarp with erect filaments, each cell producing 3 pericentral cells which divide to form a layer of irregularly shaped cells; carposporophyte much branched, with a basal fusion cell and terminal rows of ovoid carposporangia 20–40 µm in diameter. Spermatangial branches as ultimate branches of pseudolaterals, cylindrical, 100–250 µm long and 40–55 µm in diameter, with a 1–2-celled pedicel and 3–5-celled sterile tip. Tetrasporangial stichidia 100–700 µm long and 100–150 µm in diameter, becoming fertile when very short, occurring as branches of pseudolaterals with a 2–3-celled pedicel and short sterile tip, with 4 tetrasporangia per segment each with (1–)2 pre-sporangial cover cells each divided transversely; tetrasporangia 40–50 µm in diameter.

Distribution. Champion Bay, W. Aust., to Kangaroo I., S. Aust.

[After Parsons & Womersley in Womersley, Mar. Benthic Fl. Southern Australia IIIC: 483–484 (1998)]