Electronic Flora of South Australia Species Fact Sheet

Homoeostrichus olsenii Womersley sp. nov.

Phylum Phaeophyta – Order Dictyotales – Family Dictyotaceae – Tribe Zonarieae

Thallus (Fig. 85C) grey to grey-brown, sometimes slightly farinaceous, (5–) 8–15 cm long, flabellate when young and splitting to form irregularly laterally branched, essentially corn-planate, fronds with stupose lower axes 1–3 mm thick and a matted rhizoidal holdfast 3–15 mm across and 2–12 mm long; epilithic. Fronds with broad, rounded. flabellate apices 5–10 (–15) mm across in mature plants, tapering to the base of laterals usually (1–) 2–4 mm broad, often with concentric growth zones. Growth (Fig. 87B) by a marginal row of apical cells, segmenting posteriorly (Fig. 87C) when actively growing; when relatively inactive, each apical cell is wedge-shaped in longitudinal section (Fig. 87E), segments on two faces, and is largely overlain on both surfaces by derivative cells (Fig. 87D,E). Structure (Fig. 87C,G,H) 5 cells and (90–) 100–120 µm thick throughout (occasionally 6 cells thick by division of one cell), with cells in regular rows in transverse section of fronds; cortical cells the same size as medullary cells in transverse section (Fig. 87G), 2–4 (–6) to each medullary cell in longitudinal section (Fig. 87C), 20–25 µm across in surface view and L/B (1–) 1.5–2 (–3). Phaeophycean hairs absent. Paraphyses in prominent scattered tufts (Fig. 87A) or more or less concentric groups, mainly on one (the lower?) side, 12–16 (–19) cells long, 26–30 µm in diameter with cells L/B 2–3 in mid and lower parts, tapering slightly to their apices with the apical cell with a rounded end (Fig. 87F); cell divisions apical and subapical; cells thick-walled, with numerous phaeoplasts.

Reproduction: Sporangia (Fig. 87G,H) in compact, irregularly shaped, scattered, indusiate sort on the lower side, sometimes associated with paraphyses, ovoid, 80–110 (–120) µm long and 50–70 µm in diameter, with a stalk cell, dividing irregularly into four spores. Sexual reproduction unknown.

Type from Pope Eye, Port Phillip Heads, Vic., 2–9 m deep (Kain & Engler, 31.viii.1981); in ADU, A55409.


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

Distribution: From Nora Creina, S. Aust. to Walkerville, Vic. and south-east Tasmania; Port Jackson, N.S.W.)

Taxonomic notes: Homoeostrichus olsenii is usually a deep water (to 48 m) alga, occurring only rarely in heavily shaded upper sublittoral pools. It appears to be confined to south-eastern Australian waters. The species is named after Mr A.M. Olsen, then Harvesting Manager, Alginates Australia, who first collected this alga.

References: The Marine Benthic Flora of Southern Australia Part II

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 85C, 87.

Figure 85 image

Figure 85   enlarge

Fig. 85. A. Honweostrichus canaliculatus (ADU, A 18976). B. Homoeostrichus sinclairii (ADU, A19171). C. Homoeostrichus olscnii (ADU, A55409, holotype).

Figure 87 image

Figure 87   enlarge

Fig. 87. Homoeostrichus olsenii (A,D–G, ADU, A55409, holotype; B,C, ADU, A34490). A. Surface view of upper thallus with tufts of paraphyses and immature and mature sori of sporangia . B. Surface view of active apical cells. C. Longitudinal section showing segmentation from an active apical cell. D. Surface view of inactive apical cells. E. Longitudinal sections of four inactive apices, showing segmentation of apical cell. F. A paraphysis. G. Transverse section of thallus with a young sorus of sporangia and paraphyses. H. Longitudinal section with two mature tetrasporangia and paraphyses.


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