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Holmsella australis Noble & Kraft 1983: 393, figs 1–15.

Phylum Rhodophyta – Class Florideophyceae – Order Gracilariales – Family Pterocladiophilaceae

Thallus (Fig. 1A, B) white, pulvinate, surface smooth (tetrasporangial) or verrucose (cystocarpic), 0.5–3 mm across, growing on Gracilaria ramulosa (or G. flagelliformis). Structure multiaxial, with slender filaments penetrating between the host cells and pit-connecting with them, externally with a mass of compact filaments forming the pustules with a thick gelatinous outer layer below 1–2 layers of host cortical cells raised up by the parasite.

Reproduction: Gametangial thalli dioecious. Carpogonial branches (Fig. 1E) 2-celled, borne on a supporting cell which is an intercalary cell of cortical filaments. Gonimoblast filaments radiating horizontally as a basal layer of hyaline filaments with frequent fusions with gametophytic cells, and erect clusters of gonimoblast filaments (Fig. 1C) which produce chains of carposporangia, 8–12 µm in diameter, amongst a lax palisade of cortical filaments. Spermatangia (Fig. 1F) borne on outer cortical cells in chains of 2–6, each about 4 µm in diameter.

Tetrasporangia (Fig. 1D, G) developed in terminal cortical cells scattered between sterile cortical filaments, ovoid, 30–40 µm long and 15–20 µm in diameter, decussately divided.

Type from Flinders, Vic., on Gracilaria furcellata (= G. ramulosa), 2–5 m deep (Kraft, 23.xi.1976); holotype and isotypes in MELU, K6230.

Selected specimens: Whitford Beach, Perth, W. Aust., 6 m deep on Gracilaria flagelliformis (Cook, 20.viii.1979; AD, A50580). Portland, Vic., drift at Whalers Point on G. ramulosa (Muir, 17.i.1950; AD, A63231) and drift in harbour on G. ramulosa (Womersley, 14.iv.1994; AD, A63536 -"Marine Algae of southern Australia" No. 376). Queenscliff, Vic., drift on G. ramulosa (Womersley, 8.iv.1959; AD, A22851). San Remo, Vic., drift on G. ramulosa on back beach (Sinkora A2017, 27.xi. — 5.xii.1974; AD, A62465). Orford, Tas., 4–5 m deep on G. ramulosa (Kraft 9271, 15.xii.1992; MELU).

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

Distribution: Whitford Beach, Perth, W. Aust., and from Portland to San Remo, Vic.; Orford, Tasmania.

Taxonomic notes: Holmsella australis is a small but distinctive parasite, mainly on Gracilaria ramulosa on Victorian coasts but also known on G. flagelliformis near Perth, Western Australia. It is probably more widespread in southern Australia.


NOBLE, J.M. & KRAFT, G.T. (1983). Three new species of parasitic red algae (Rhodophyta) from Australia: Holmsella australis sp. nov., Meridiocolax bracteata sp. nov. and Trichidium pedicellatum gen. et sp. nov. Br. phycol. J. 18, 391–413.

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

Author: H.B.S. Womersley

Publication: Womersley, H.B.S. (28 June, 1996)
The Marine Benthic Flora of Southern Australia
Rhodophyta. Part IIIB. Gracilarialse, Rhodymeniales, Corallinales and Bonnemaisoniales
Reproduced with permission from The Marine Benthic Flora of Southern Australia Part IIIB 1996, by H.B.S. Womersley. Australian Biological Resources Study, Canberra. Copyright Commonwealth of Australia.

Illustration in Womersley Part IIIA, 1996: FIG. 1.

Figure 1 image

Figure 1   enlarge

Fig. 1. Holmsella australis (A, B, MELU, K6230; C, D, AD, 63536). A. Two sexual thalli, each lobe containing a carposporophyte. B. A tetrasporangial thallus. C. Section through a female thallus with a mature carposporangial layer (arrow). D. section of a tetrasporangial thallus. E. Section of female thallus with carpogonial branches. F. Section of male thallus with spermatangia. G. Section of tetrasporangial thallus. (In E–G, cells of the host are shown above.) B, E–G, after Noble & Kraft 1983.

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