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Genus AMPHIPLEXIA J. Agardh 1892: 104

Phylum Rhodophyta – Class Florideophyceae – Order Gigartinales – Family Acrotylaceae

Thallus erect, with clavate and saccate branches, apices rounded and basally constricted, branching from the apices, circular in cross section; holdfast discoid to crustose and knobby. Structure multiaxial, with a very lax medulla (dense below) of scattered filaments, mucilaginous, and a pseudoparenchymatous cortex with a large-celled, single, inner layer and a small-celled outer cortex 1–2 cells thick, surface view rosette-like or evenly covered.

Reproduction: Sexual thalli monoecious; procarpic; monocarpogonial. Carpogonial branches borne singly on inner cortical cells, 3-celled, directed inwards with reflexed trichogynes. Fertilized carpogonium connecting to the supporting (auxiliary) cell by a short tube, with gonimoblast initials formed towards the thallus surface, and with adjacent vegetative cells cutting off nutritive cells which partly surround the auxiliary cell and line the base of the cystocarp; gonimoblast filaments lining a cavity which develops above the auxiliary cell and is surrounded by prominent enveloping tissue and a pericarp developed from the outer cortex, with the gonimoblast filaments branching and developing centripetally with rows of 2–3 ovoid carposporangia. Cystocarps protuberant, often basally constricted, ostiolate. Spermatangia in scattered clusters, produced from outer cortical cells.

Tetrasporangia scattered in outer cortex, derived from mid-cortical cells and often intercalary, zonately divided.

Life history triphasic, with isomorphic gametophytes and tetrasporophytes.

Type species: A. hymenocladioides J. Agardh 1892: 111.

Taxonomic notes: A genus of two species (the type and A. racemosa) confined to southern and western Australia. While the genus shows most of the reproductive features of the Acrotylaceae, it differs in the restricted development of nutritive cells, outward gonimoblast orientation, formation of the cystocarp cavity by growth of the pericarp and not by breakdown of the auxiliary cell, and the direct association of gonimoblast filaments with the pericarp. Further studies may show it should be placed in a separate family from the Acrotylaceae.


AGARDH, J.G. (1892). Analecta Algologica. Acta Univ. lund. 28, 1–182, Plates 1–3.

The Marine Benthic Flora of Southern Australia Part IIIA complete list of references.

Author: G.T. Kraft & H.B.S. Womersley

Publication: Womersley, H.B.S. (14 January, 1994)
The Marine Benthic Flora of Southern Australia
Rhodophyta. Part IIIA, Bangiophyceae and Florideophyceae (to Gigartinales)
Reproduced with permission from The Marine Benthic Flora of Southern Australia Part IIIA 1994, by H.B.S. Womersley. Australian Biological Resources Study, Canberra. Copyright Commonwealth of Australia.


1. Thallus without prominent main axes, surface cells forming rosettes around large inner cortical cells

A. hymenocladioides

1. Thallus with prominent main axes, branch systems often pyramidal in form, surface cells covering larger inner cortical cells without rosettes

A. racemosa

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