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Hapalospongidion capitatum Womersley sp. nov.

Phylum Phaeophyta – Order Chordariales – Family Ralfsiaceae

Thallus dark brown, crustose but gelatinous when fresh, a few mm across to confluent patches a cm or so across, mostly 500–750 thick, firmly adherent to the rock substrate, without rhizoids. Basal layer (Fig. 20B–D) of radiating filaments of rectangular cells 5–8 µm across, becoming 2–3 cells thick, with each cell producing two erect, simple (rarely branched) filaments transversely to the basal cell rows. Erect filaments (Fig. 20B–F) at first slightly assurgent, soon becoming separated, of 40–60 cells; most filaments with lower cells 4–6 pm in diameter and L/B 2–3, mid cells 3–4 in diameter and L/B 4–6, surmounted by 3–7 cells of increasing diameter to the subspherical to ovoid terminal cell 10–12 µ in diameter; occasional erect filaments distinctly broader (8–10 µm) throughout with the cylindrical terminal cell of similar diameter; hairs not seen. Growth of erect filaments by intercalary divisions of subapical and lower cells. Cells with one to a few laminate phaeoplasts and numerous scattered physodes (Fig. 20C,E).

Reproduction: Reproduction by plurilocular sporangia (Fig. 20G–K) originating below (often just below) the apex of erect filaments but becoming terminal by loss of upper part of filament, occasionally on short lateral branches from below another sporangium, becoming 40–60 (–80) µm long and 15–20 µm in diameter with loculi 2–4 µm across; occasional sporangia develop as, or with, lateral protrusions (Fig. 20K) and all sporangia are situated within the thallus.

Type from Frenchman Bay, King George Sound, W. Aust., mid eulittoral on granite (Womersley, 29.viii.1979); holotype in ADU, A51653.

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

Distribution: Only known from the type collection.

Taxonomic notes: Hapalospongidion capitatum is only known with plurilocular sporangia, and these are typical of the genus but more developed than in other species. It differs from the type species in the larger, capitate, uppermost 2–3 cells of the erect filaments and in having more elaborate plurilocular sporangia, and from H. saxigenum Lindauer (1949, p. 347, fig. 5j-l) from New Zealand, which does not have the capitate erect filaments and is only known with unilocular sporangia.

Mesospora schmidtii W. van Bosse and Basispora africana John & Lawson, both of which are inadequately separated from Hapalospongidion (see above) differ in that the erect filaments are considerably shorter (fewer than 40 cells) and their uppermost cells are only slightly broader than those below. Mesospora macrocarpa (Feldmann) den Hartog (1968, p. 387) from the Mediterranean has shorter erect filaments which bear lateral sporangia on short stalks and differs in this way from the type species of Mesospora. M. vanbosseae Boergesen (1924, p. 258) from Easter Island also lacks the capitate ends to the erect filaments, has a multilayered base, and the erect filaments are only 20–30 cells long.


BOERGESEN, F. (1924). Marine algae from Easter Island. In Skottsberg, C. (Ed.) The Natural History of Juan Fernandez and Easter Island. Vol. 2, pp. 247–309. (Uppsala, Sweden.)

DEN HARTOG, C. (1968). The littoral environment of rocky shores as a border between the sea and the land and between the sea and fresh water. Blumea 16, 374–393.

LINDAUER, V.W. (1949). Notes on marine algae of New Zealand. I. Pacif. Sci. 3, 340–352.

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

Illustration in Womersley Part II, 1997: FIG. 20.

Figure 20 image

Figure 20   enlarge

Fig. 20. Hapalospongidion capitatum (ADU, A51653, holotype). A. Cross-section of thallus showing basal and erect filaments with plurilocular sporangia. B. Cross-section of thallus with margin. C,D. Tangential cross-sections with basal layers and erect filaments. E. Mid parts of erect filaments. F. Upper ends of erect filaments. G–K. Stages in development of plurilocular sporangia.

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