Electronic Flora of South Australia Genus Fact Sheet

Genus ZONARIA C. Agardh 1817: xx, nom. cons.

Phylum Phaeophyta – Order Dictyotales – Family Dictyotaceae – Tribe Zonarieae

Thallus erect, 5–25 cm long, flabellate or usually becoming much branched by apical splitting, usually stupose in lower parts (especially in centre of branches) and with a matted rhizoidal holdfast. Growth by a marginal row of apical cells on each branch. Fronds often broader basally or when young, upper branches I mm to 4 cm broad, complanate but often twisted, occasionally with a faint, central "midrib" due to darker cells (not thickened). Branches in some species with faint concentric zones of growth or of hairs. Structure (4–) 6–10 cells thick, of uniform small size and in regular rows in transverse section (cells usually less than 25 µm across), elongate in longitudinal section; cortical cells generally or frequently once subdivided as seen in transverse section compared to medullary cells, in longitudinal section with 4–8 cells corresponding to each medullary cell; phaeoplasts dense in cortical cells, less so in medullary cells. Hair tufts phaeophycean, scattered or in concentric zones, apparently absent in some species.

Reproduction: Sporangia in scattered sori, with (or without in Z. angustata) cellular paraphyses, each with eight spores. Sexual plants rare, with scattered sori of oogonia or antheridia.

Life history diplohaplontic and isomorphic, in some species probably direct from the sporophyte.

Lectotype species: Z. tiara (Clemente) C. Agardh [Z. tournefortii (Lamouroux) Montagne]. A genus of some 10 species, well represented in the southern hemisphere.

Taxonomic notes: Zonaria is characterised by the regularity and small size of cells of the thallus, longitudinal subdivision of most cortical cells, the presence of paraphyses in sporangial sori of most (but not all) species, and sporangia with 8 spores. It is often not possible to determine a species unless the specimen is well developed and fertile; young plants usually have broader branches than when mature.

Homoeostrichus J. Agardh was united by Papenfuss (1944, p. 340) with Zonaria, but is re-established above for species with only four spores per sporangium and with few cortical cells becoming paired.


AGARDH, C.A. (1817). Synopsis Algarum Scandinaviae. (Lund.)

PAPENFUSS, G.F. (1944). Notes on algal nomenclature. III. Miscellaneous species of Chlorophyceae, Phaeophyceae and Rhodophyceae. Farlowia 1, 337–346.

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


1. Thallus branches 1–2 (–3) mm broad, irregularly linear and not regularly twisted; sporangial sori without multicellular paraphyses

Z. angustata

1. Thallus branches either 1–2 (–3) mm broad and regularly spirally twisted, or 2–10 mm broad at least near the apices; sporangial sori with multicellular paraphyses


2. Thallus with slender, usually denuded, lower parts and flabellate apices 4–10 mm broad; upper branches covered by a network of hydroid; thallus 6 cells thick

Z. crenata

2. Thallus complanate or spirally twisted, of similar width throughout; not covered by a network of hydroid; thallus 8 (–10) cells thick


3. Thallus branches regularly spirally twisted, 1–2 (–3) mm broad

Z. spiralis

3. Thallus branches complanate, not regularly twisted, 2–4 mm broad

Z. turneriana

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