Electronic Flora of South Australia Family Fact Sheet

FAMILY HYPNEACEAE J. Agardh 1851: viii

Phylum Rhodophyta – Class Florideophyceae – Order Gigartinales

Thallus erect (or parasitic and pulvinate-lobed), much branched irregularly usually with numerous short laterals, branches terete to compressed, holdfast discoid to fibrous and entangled. Structure uniaxial, with a distinct protruding apical cell, axial filament distinct throughout, with a large-celled pseudoparenchymatous medulla grading to a small-celled cortex 1–3 cells broad; inner cells multinucleate, linked by secondary pit-connections, often with lenticular secondary wall thickenings; outer layer of cortex continuous, without rosettes.

Reproduction: Sexual thalli dioecious; procarpic and monocarpogonial. Carpogonial branches 3-celled, borne laterally to outwardly on inner cortical cells. Auxiliary cells intercalary, next outwardly to the supporting cells, diploidized by direct fusion or a short process. Gonimoblast initial single, inwardly directed and often developing a basal nutritive tissue, branching to form a reticulum of elongate cells which cut off numerous clusters of small cells producing radially single, relatively large, carposporangia. Cystocarps protuberant, usually sub-spherical, sessile, with a thick pericarp of small cells in anticlinal chains, usually non-ostiolate. Spermatangia cut off from outer cortical cells of small laterals.

Tetrasporangia formed in swollen sori or nemathecia partly or completely surrounding the base of short lateral branchlets, zonately divided.

Life history triphasic with isomorphic gametophytes and tetrasporophytes.

Taxonomic notes: A family with two genera, the common genus Hypnea with numerous species, and the parasitic genus Hypneocolax.

The Hypneaceae are characterised particularly by the carposporophyte structure, consisting of a reticulum of elongate cells with numerous discrete clusters of small cells bearing single carposporangia, as illustrated by Kylin (1930, fig. 39A, B) for the type species of Hypnea. This is distinct from the carposporophyte of the Cystocloniaceae which is an erect, branched, structure with terminal chains of carposporangia. In vegetative structure and other reproductive details these two families are similar, though members of the Hypneaceae normally have a uniform outer cortical layer in contrast to the rosettes of the Cystocloniaceae.

References:

AGARDH, J.G. (1851). Species Genera et Ordines Algarum. Vol. 2, Part 1, 1–336 + index. (Gleerup: Lund.)

KYLIN, H. (1930). über die entwicklungsgeschichte der Florideen. Lunds Univ. Årsskr. N.F. Avd. 2, 26 (6), 1–104.

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

Author: 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.

KEY TO GENERA OF HYPNEACEAE

1. Thallus erect or basally entangled, much branched usually with numerous short lateral branchlets, several to many cm high, branches terete to compressed; cystocarps globular, sessile on branches; tetrasporangia in sori around the base of short lateral branchlets

HYPNEA

1. Thallus 0.2–2 mm high, pulvinate and lobed to stellate, parasitic on Hypnea

HYPNEOCOLAX


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