Electronic Flora of South Australia Genus Fact Sheet

Genus PERITHALIA J. Agardh 1890: 1

Phylum Phaeophyta – Order Sporochnales

Thallus (sporophyte) 20–100 cm long, much branched with numerous fastigiate axes and long laterals, each terminating with a rounded apex or a cupulate cap covering the apex, formed from laterally adherent bases of trichothallic filaments which only occasionally occur as a free tuft; holdfast becoming massive, woody. Growth from an apical, convex branch meristem surmounted by the cap of trichothallic assimilatory filaments. Structure haplostichous and pseudoparenchymatous, with a medullary core of elongate cells and a cortex increasing in thickness by periclinal (largely) divisions of the outer layer of cells; surface smooth.

Reproduction: Sporangial sori compact, surrounding the lesser branches a short distance below their apices, composed of densely grouped, simple, slightly clavate paraphyses with unilocular sporangia borne on the basal cell.

Gametophytes dioecious, forming oogonia or antheridia producing a single sperm.

Life history diplohaplontic and hetermorophic, with a microscopic, filamentous, oogamous gametophyte.

Type species: P. inermis (Turner) J. Agardh [=P. caudata (Labillardière) Womersley].

Taxonomic notes: A genus of two species, the type and P. capillaris from New Zealand. The type species is distinctive in habit, in the capitate branch apices with the trichothallic assimilatory filaments only occasionally forming a free tuft but spreading over the rounded apex and adhering laterally to form the cap, in the position of the sporangial sori some distance below the branch apices, and in the holdfast which can become massive with numerous axes arising from it.

The position of the sporangial sori is mirrored in Sporochnus by S. stylosus, but Perithalia differs in habit and the apical branch caps.


AGARDH, J.G. (1890). Till algernes systematik. Ada Univ. lund. 26(3), 1–125, Plates 1–3.

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
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