Electronic Flora of South Australia Species Fact Sheet

Pseudolithoderma australis Womersley sp. nov.

Phylum Phaeophyta – Order Chordariales – Family Ralfsiaceae

Thallus (Fig. 15C) medium to dark brown, crustose, forming smooth-surfaced patches with rounded to indented margins, 0.5–3 cm across or irregularly spreading, on rock (and on plastic), fairly firmly adherent, without rhizoids. Basal layer of radiating filaments with apical (marginal) growth (Fig. 19D,E), of oblong cells 6–12 µm broad and L/B 1–2 just within the margin, becoming 12–15 µm broad and L/B 2–3 in older parts, each cell dividing horizontally to form a distinct basal layer 2–4 cells thick (Fig. 19F,G). Erect filaments (Fig. 19F,G) arising shortly behind the margin, usually in pairs, from each upper cell of the basal layer, remaining short for some distance from the margin, then elongating rapidly to their mature height (Fig. 19G), separating moderately readily under pressure; filaments cylindrical and of uniform height, simple or occasionally with 1–2 (–3) branches either below or near their apices, of (6–) 16–20 cells each 10–12(46) µm in diameter and L/B (0.5–) 1–1.5 (–2), apical cell with rounded apex (Fig. 19F,G). Growth of erect filaments by divisions of the apical or subapical cells. Cells with several [3–8 (or more in young basal cells)] discoid to slightly elongate phaeoplasts, and few, prominent physodes (Fig. 19F–H). Phaeophycean hairs present in clusters, originally arising from the basal layer.

Reproduction: Reproduction by large, cylindrical to clavate, unilocular sporangia (Fig. 19F,G), 30–50 µm long and 10–16 µm in diameter, borne terminally on erect filaments, either close to the basal layer or within the upper thallus but below the surface; contents of the sporangia in some collections are mostly yellowish and even, with few showing divisions to form zoospores. Plurilocular sporangia (Fig. 19H) uniseriate with 5–8 loculi, oblong-ovoid, 22–30 µm long and 12–16 µm in diameter.

Type from Abalone Cove, West I., S. Aust., 5 m deep on plastic bottle and on old shells (Shepherd, 2.iii.1983; holotype in ADU, A54022).


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

Distribution: Known from the type and from Head of Great Australian Bight, S. Aust., upper sublittoral in shaded pool ( Womersley, 4.ii.1954; ADU, A19320). Port Stanvac, S. Aust., 1.5 m deep on hard plastic sheet (Clarke & Engler, 30.iii.1978; ADU, A49223) and in mid eulittoral pool (Clarke, 21.xi.1984; ADU, A56210). West I., S. Aust., 5 m deep (Shepherd, 27.vii.1984; ADU, A56275). Middle River, Kangaroo I., S. Aust., upper sublittoral on rock, west side of mouth (Womersley, 21.i.1948; ADU, Al2974-with plurilocular sporangia). Shelter Point, Boat Harbour Beach, N. Tas., in large, low eulittoral pool (Womersley, 16.x.1982; ADU, A55733).

Taxonomic notes: Pseudolithoderma australis is known only from the above collections, of which Al2974 is plurilocular and on rock; the type and Port Stanvac collections were mostly on hard plastic. It differs from other species of the genus in having the large, unilocular sporangia, which are terminal on erect filaments, sunken within the thallus at various levels; in other species, the unilocular sporangia form a surface layer. Most of the sporangia have uniform yellowish contents, and only a few were seen showing signs of division of the contents to form zoospores. Plurilocular sporangia are uniseriate and large in the one collection seen, and are terminal on erect filaments. This also differs from the biseriate plurilocular sporangia of other species (e.g. P. nigrum-Hollenberg 1969, fig. 19; P. subextensum-Tanaka & Chihara 1981, fig. 2A) and placement in Pseudolithoderma is provisional. Ascocysts such as those in P. nigrum Hollenberg (1969, p. 297, fig. 19) from California and in P. subextensum (Tanaka & Chihara 1981, p. 379) from Japan have not been observed.

References:

HOLLENBERG, G.J. (1969). An account of the Ralfsiaceae (Phaeophyta) of California. J. Phycol. 5, 290–301.

TANAKA, J. & CHIHARA, M. (1981). Taxonomic study of the Japanese crustose brown algae (6). Pseudolithoderma (Lithodermataceae, Ralfsiales). J. Jap. Bot. 56, 376–381.

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

Author: H.B.S. Womersley

Publication: Womersley, H.B.S. (14 December, 1987)
The Marine Benthic Flora of Southern Australia
Part II
©Board of the Botanic Gardens and State Herbarium, Government of South Australia


Illustrations in Womersley Part II, 1997: FIGS 15C, 19 D–H.

Figure 15 image

Figure 15   enlarge

Fig. 15. A. Myrionema strangulans (ADU, A29639). B. Ralfsia verrucosa, on limpets and rock (ADU, A15364). C. Pseudolithoderma australis on plastic (ADU, A54022, holotype). D. Halothrix ephemeralis (ADU, A32664, holotype).

Figure 19 image

Figure 19   enlarge

Fig. 19. A–C. Ralfsia verrucosa (A,C, ADU, A15364; B, ADU, Al2921). A. Radial section showing assurgent filaments, phaeophycean hairs and unilocular sporangia. B. Upper thallus with plurilocular sporangia. C. Filament with a unilocular sporangium and paraphysis; cells with a single phaeoplast and physodes. D–H. Pseudolithoderma australis (D–G, ADU, A54022, holotype; H, ADU, Al2974). D. Part of thallus showing basal layer, erect filaments (below) and tufts of hairs. E. Margin of thallus with early stages of erect filaments (two from each basal cell). F. Radial cross-section with unilocular sporangia and a phaeophycean hair. G. Tangential cross-section of an older thallus with unilocular sporangia. H. Cross-section of thallus with plurilocular sporangia.


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