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Electronic Flora of South Australia Genus Fact Sheet

Genus HYMENOCLADIA J. Agardh 1852: 772

Phylum Rhodophyta – Class Florideophyceae – Order Rhodymeniales – Family Rhodymeniaceae

Thallus erect, variously branched usually complanately, often proliferous from the margins, foliose, pinnate or subdichotomous, branches flat, compressed or terete; holdfast discoid, epiphytic on Amphibolis or other algae, or epilithic. Structure multiaxial, developing a cortex (1–) 2–6 cells thick and a medulla of large ovoid cells from which smaller cells or filaments are cut off; secretory cells absent in most species.

Reproduction: Gametangial thalli monoecious or dioecious; procarpic. Carpogonial branches 4-celled, borne on inner cortical supporting cells together with a 2-celled auxiliary cell branch. Carposporophyte developing outwards, with a basal fusion cell and branched system of lower darkly staining cells, with the upper cells all forming relatively large carposporangia, often with later lobes developing. Basal nutritive tissue well developed, with the erect filaments largely disintegrating but thick-walled remnant cells often remaining near the nutritive tissue. Cystocarps external, hemispherical to conical, with a thick pericarp, ostiolate. Spermatangia in surface sofi, cut off from elongate initials on cortical cells.

Tetrasporangia scattered, transformed from intercalary inner cortical or outer medullary cells, relatively large (60–140 µm in diameter), tetrahedrally divided.

Life history triphasic with isomorphic gametophytes and tetrasporophytes.

Type species: H. usnea (R. Brown ex Turner)J. Agardh 1852: 772.

Taxonomic notes: A genus of six species, confined to southern Australia, New Zealand and South Africa.

Hymenocladia is characterised by the medullary structure of large and small cells (or filaments) intermixed, and by the very large intercalary, tetrahedrally divided, tetrasporangia (and also large carposporangia).

References:

AGARDH, J.G. (1852). Species Genera et Ordines Algarum. Vol. 2, Part 2, pp. 337–720. (Gleerup: Lund.)

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

Author: H.B.S. Womersley

Publication: Womersley, H.B.S. (28 June, 1996)
The Marine Benthic Flora of Southern Australia
Rhodophyta. Part IIIB. Gracilarialse, Rhodymeniales, Corallinales and Bonnemaisoniales
Reproduced with permission from The Marine Benthic Flora of Southern Australia Part IIIB 1996, by H.B.S. Womersley. Australian Biological Resources Study, Canberra. Copyright Commonwealth of Australia.

KEY TO SPECIES OF HYMENOCLADIA

1. Thallus foliose to much branched or marginally lobed, mostly 2–10 cm broad

H. chondricola

1. Thallus much branched, branches terete to flattened, less than 1 cm broad

2

2. Branches slightly compressed, 0.5–1 mm broad

H. filiformis

2. Branches (at least the axes) compressed, 2–8 mm broad

3

3. Axes 2–8 mm broad, ramuli compressed and 1–2 mm broad

H. usnea

3. Axes 2–3 (–5) mm broad, ramuli terete or subterete, (100–) 150–250 µm broad

H. divaricata


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