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Electronic Flora of South Australia Genus Fact Sheet
Phylum Phaeophyta – Order Sphacelariales – Family Stypocaulaceae
Thallus 3–15 (–30) cm long, forming dense tufts, usually epilithic, in most species attached by a matted holdfast of descending rhizoidal filaments arising from cells of the axes, in a few species with a basal discoid holdfast without descending rhizoids. Erect filaments much branched with numerous axes bearing radially or distichously arranged laterals, some indeterminate but most determinate; internal structure of larger medullary cells covered by a small-celled monostromatic cortex which becomes more than one layered only in older axes of H. paniculata, and in most species (except H. platycena) is further corticated by descending rhizoidal filaments. Growth apical, acroblastic.
Reproduction: Reproduction of sexual plants oogamous; asexual plants with unilocular sporangia borne in axils of laterals.
Type species: H. filicina (Grateloup) Kützing.
Taxonomic notes: Halopteris is a common and distinctive genus on southern Australian coasts, with five species; some are common just subtidally, on rock platforms and in pools, while most species extend into deep water. Sexual plants are rare in all species.
Kützing (1843, pp. 292, 293) distinguished two genera, Halopteris and Stypocaulon [type species S. scoparim (L.) Kützing], which differ in that Halopteris is distichously branched and Stypocaulon radially. Further, the axes of Halopteris show in cross section radial divisions with four large central cells, pericysts are absent, and rhizoids develop from first-order laterals. In Stypocaulon, the axes in cross section show a large number of small, squarish cells developed by periclinal divisions, pericysts are present, and rhizoidal filaments develop from pericysts. On the above basis, Halopteris would include H. platycena and H. ramulosa, with Stypocaulon including the other Australian species. H. platycena also differs in not forming rhizoidal filaments on the lower axes, and thus resembles Phloiocaulon, which then differs from Halopteris in having an extensive secondary cortex to the axes and laterals with auxocaulic growth, in lacking descending rhizoids, and in anisogamous sexual reproduction.
Sauvageau, Prud'homme van Reine and other authors have considered the differences involved inadequate to separate generically Halopteris and Stypocaulon.
References:
KÜTZING, F.T. (1843). Phycologia generalis. (Leipzig.)
The Marine Benthic Flora of Southern Australia Part II complete list of references.
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
KEY TO SPECIES OF HALOPTERIS
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1. Thallus axes and laterals essentially alternately distichously branched a few segments apart, at least near the base; rhizoidal cortication slight, only near the base; sporangia borne singly in axils of ramuli | 2 |
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1. Thallus with alternately distichous or radial branching several to many segments apart; rhizoidal cortication well developed, extending well above the base; sporangia borne in dense axillary clusters | 3 |
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2. Thallus with a discoid, cellular holdfast, without descending rhizoids clothing the axes; sporangia borne singly on a unicellular pedicel in axils of laterals | H. platycena |
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2. Thallus with a rhizoidal holdfast and descending rhizoids on lower axes; basal and upper parts morphologically distinct, with sporangia borne singly on a | H. novae-zelandiae |
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3. Thallus branching alternately distichous | H. ramulosa |
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3. Thallus branching irregularly radial | 4 |
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4. Slight secondary cortex present on axes and main laterals; reproductive organs in axils of ramuli forming dense terminal spikes, with the ramuli (bracts) sharply reflexed upwards (and laterally in sporangial plants) | H. paniculata |
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4. Secondary cortex absent; reproductive organs in axils of normal ramuli but not forming dense terminal spikes | 5 |
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5. Sporangial sori with curved, sterile, paraphyses over-arching sporangia; sex organs on much-branched axillary filaments | H..funicularis |
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5. Sporangial sori dense, without sterile paraphyses, sporangia reaching similar height to form a hemispherical mass; sex organs on few-celled, simple or slightly branched pedicels | H. pseudospicata |
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