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Heterostroma nereidiis Kraft & Wynne 1992: 18, figs 2–36.

Phylum Rhodophyta – Family Rhodomelaceae – Tribe Pterosiphonieae

Thallus (Fig. 149F) medium to dark brown-red, with decumbent fronds 1–4 cm long arising from prostrate, imbricate to expanded, bases to 280 µm thick. Fronds complanately and pinnately branched for 3–4 orders, branches (1–) 2–3 (–4) mm broad and 60–130 µm thick, margins irregularly serrate with alternate, pointed, determinate laterals (Fig. 149G), all with distinct apices and some becoming indeterminate. Attachment by clumped rhizoids from the ventral surface; epilithic or epiphytic on Amphibolis or on encrusting corallines on larger algae. Structure. Apical cells short-conical to dome-shaped, 15–20 µm in diameter, subapical cells cutting off first lateral branch initials then 4 pericentral cells with 2 lying on each of the dorsal and ventral surfaces which become heteromorphic by different divisions but remain ecorticate. The axial cells branch alternately laterally every 2 cells and also produce unicellular primordia from alternate cells on alternate sides; however, inner parts of secondary laterals may be branched 4–7 axial cells apart. Dorsal pericentral cells divide transversely and longitudinally to produce angular cells 15–30 µm across and L/D 1–2, lying over the larger ventral cells which divide only longitudinally, remaining 40–75 (–140) µm in diameter and L/D (2–) 3–4. Trichoblasts occur only associated with reproductive organs but are well developed, branched and 0.5–1.5 mm long. Rhizoids unicellular, cut off from the pericentral cells and with multicellular haptera.

Reproduction: All reproductive organs borne on short terete marginal processes with 5 pericentral cells and trichoblasts. Gametophytes dioecious. Procarps on the second cell of trichoblasts, with a 4-celled carpogonial branch and 2 sterile groups. Cystocarps (juvenile) ovoid; pericarp ostiolate, with about 11 erect filaments, probably ecorticate. Spermatangial organs borne as one basal branch of trichoblasts, elongate-ovoid, 130–200 µm long and 50–60 µm in diameter, with 7–9 fertile segments each with 3 pericentral cells, producing a layer of initials and a surface layer of spermatangia.

Tetrasporangial stichidia (Fig. 149H) occur marginally, single or grouped and bearing terminal trichoblasts, irregularly twisted or distorted by the sporangia, stichidia (0.25–) 0.5–1.2 mm long and 150–200 µm in diameter, each segment with 5 pericentral cells and a single tetrasporangium, spirally arranged, 50–100 µm in diameter, with 3 cover cells.

Type from Yanchep, W. Aust., on stems of Amphibolis antarctica, drift (G., L. & I. Kraft, 20.ix.1990); holotype MELU, K17001, isotypes K17002–17004.

Selected specimens: Point Clune, Rottnest I., W. Aust., on Zonaria, 13–14 m deep (Kraft & Ricker, 2.xii.1980; MELU, A35328 and AD, A69069). Elliston, S. Aust., 10–12 m deep on limestone in centre of bay (Shepherd, 24.x.1969; AD, A34969).

Distribution map based
on current data relating to
specimens held in the
State Herbarium of SA

Distribution: Houtman Abrolhos to Rottnest I., W. Aust., and Elliston, S. Australia.

Taxonomic notes: Heterostroma nereidiis has a wide distribution on western and southern Australian coasts but is apparently a rare alga, easily overlooked. The Elliston specimen is tetrasporangial and agrees well with the type description.


KRAFT, G.T. & WYNNE, M.J. (1992). Heterostroma nereidiis gen. et. sp. nov. (Rhodophyta), a dorsiventral rhodomelaceous marine alga from Western Australia. Phycologia 31, 16–36.

The Marine Benthic Flora of Southern Australia Part IIID complete list of references.

Publication: Womersley, H.B.S. (24 February, 2003)
The Marine Benthic Flora of Southern Australia
Rhodophyta. Part IIID. Ceramiales – Delesseriaceae, Sarcomeniaceae, Rhodomelaceae
Reproduced with permission from The Marine Benthic Flora of Southern Australia Part IIID 2003, by H.B.S. Womersley. Australian Biological Resources Study, Canberra. Copyright Commonwealth of Australia.

Illustration in Womersley Part IIIA, 2003: FIG. 149 F–H.

Figure 149 image

Figure 149   enlarge

Fig. 149. A–E. Symphyocladia marchantioides (A–C, AD, A59223; D, MELU, K6615, slide; E, AD, A69070). A. Habit. B. Flat branch apex with congenitally fused polysiphonous filaments, showing vein system. C. Margin of branch with trichoblasts. D. Transverse section of branch showing 8 pericentral cells. E. Branch with tetrasporangia. F–H. Heterostroma nereidiis (AD, A34969). F. Habit. G. Branch apex with alternate spinous determinate laterals. H. Stichidia on blade margin.

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