Electronic Flora of South Australia Genus Fact Sheet

Genus MACROCYSTIS C. Agardh 1820: 46

Phylum Phaeophyta – Order Laminariales – Family Lessoniaceae

Thallus usually 3–30 (–100) m long, with a much branched holdfast of subdichotomous haptera, usually becoming conical, bearing numerous erect fronds. Growth of young blades by splitting through the transition region, becoming sub-terminal as the blades develop from the falcate apices, with each lateral developing a basal pneumatocyst. Stipes long (1–30 m), terete, bearing blades unilaterally. Blades (laterals) simple, 0.3–2 m long and usually 2–10 cm broad, relatively thin, ligulate, margins usually spinous, surface smooth to rugose, with a large, basal subspherical to elongate pneumatocyst. Structure of a central, filamentous medulla with sieve-tube like elements (especially in the stipes), and an extensive cortex of relatively small cells with a surface meristoderm; outer cells densely phaeoplastic.

Reproduction: Reproduction by unilocular sporangia (with paraphyses) in ovate to subcircular or irregular sori on basal blades adjacent to the holdfast.

Lectotype species: M. pyrifera (Linnaeus) C. Agardh.

Taxonomic notes: Gametophytes dioecious, filamentous, oogamous, the female less branched and with larger cells than the male.

Numerous species have been described in Macrocystis, but these were reduced to three by Womersley (1954a). Since then, M. laevis Hay (1986) has been described from Marion Island in the southern Indian Ocean.

References:

AGARDH, C.A. (1820). Species Algarum. Vol. 1, Part 1, Fucoideae, pp. 1–168. (Lund.)

HAY, C. (1986). A new species of Macrocystis C. Ag. (Phaeophyta) from Marion Island, southern Indian Ocean. Phycologia 25, 241–252.

WOMERSLEY, H.B.S. (1954a). The species of Macrocystis, with special reference to those on southern Australian coasts. Univ. Calif Publ. Bot. 27, 109–132.

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

KEY TO SPECIES OF MACROCYSTIS

1. Mature holdfast consisting of one(–3) central, terete to slightly compressed, erect axes (the base of the stipe) from which dichotomous haptera arise on all sides; blades usually 5–15 cm broad; splitting apex broadly falcate, with 8–20 partially separate young blades

M. pyrifera

1. Mature holdfast consisting of stoloniferous branches; several to many in each holdfast, slightly compressed and 4–8 (–10) mm across, producing haptera mainly from their sides; blades usually 1–2.5 (–5) cm broad; splitting apex narrowly falcate, with 2–8 partially separate young blades

M. angustifolia


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