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FAMILY GRACILARIACEAE Nägeli 1847: 240,254

Phylum Rhodophyta – Class Florideophyceae – Order Gracilariales

Thallus erect and usually several to many centimetres high, or decumbent, or parasitic and pustular, when erect radially or complanately branched, branches terete to flat, usually firm and drying cartilaginous, usually on solid substrates. Structure uniaxial but axis not apparent, pseudoparenchymatous with a small-celled cortex often with anticlinal cell rows, and a large-celled medulla of multinucleate cells with numerous secondary pit-connections; cell walls containing agar.

Reproduction: Gametangial thalli dioecious. Carpogonial branches 2-celled, flanked by two or more sterile filaments on a multinucleate intercalary supporting cell. Fertilized tarpogonium fusing with adjacent cells of sterile filaments and developing gonimoblast filaments directly, with large cells thereof forming secondary pit-connections and terminal chains or clusters of carposporangia; secondary fusions of gonimoblast cells with vegetative cells in the floor of the cystocarp occur, and traversing nutritive cells or filaments ("tubular nutritive cells" or "traversing cells") from the gonimoblast to the pericarp may occur. Cystocarps protruding; pericarp thick, originating schizogenously, ostiolate. Spermatangia superficial as cortical sori or in cortical depressions or pits.

Tetrasporangia scattered in the cortex or in nemathecia, cruciately divided.

Life history triphasic with isomorphic gametophytes and tetrasporophytes.

Taxonomic notes: A family of 6 or 7 genera (see Fredericq & Hommersand 1990b), with 2 parasitic genera and 4 or 5 erect, free living, genera. Hydropuntia (syn. Polycavernosa), recognised by Fredericq & Hommersand (1990b), is often included within Gracilaria [e.g. Abbott et al. (1991)].


ABBOTT, I.A., ZHANG JUNFU & XIA BANGMEI (1991). Gracilaria mixta, sp. nov. and other western Pacific species of the genus (Rhodophyta: Gracilariaceae). Pacif. Sci. 45, 12–27.

FREDERICQ, S. & HOMMERSAND, M.H. (1990b). Diagnoses and key to the genera of the Gracilariaceae (Gracilariales, Rhodophyta). Hydrobiologia 204/205, 173–178.

NÄGELI, C. (1847). Die neueren Algensysteme und Versuch zur Begründung eines eigenen Systems der Algen und Florideen. Neue Denkschr. allg. schweiz. Ges. Naturwiss. 9, 1–275, Plates 1–10.

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.


1. Thallus usually terete (in some species compressed); cystocarps on all sides of thallus, cavity not completely filled with carposporophyte, traversing nutritive cells present or absent in cystocarp floor and pericarp, carposporangia in clusters or short chains; spermatangia in pits (conceptacles) or superficial on the cortex; tetrasporangia usually scattered in outer cortex


1. Thallus compressed (rarely subterete) to flat; cystocarps usually on or near the margins, cavity completely filled with carposporophyte, traversing nutritive cells absent, carposporangia in long chains; spermatangia in surface sori; tetrasporangia in nemathecia, between paraphyses


2. Cystocarps with traversing nutritive cells between the carposporophyte and pericarp; spermatangia in pits or conceptacles


2. Cystocarps without traversing nutritive cells; spermatangia superficial, cut off from outer cortical initials


3. Branching subdichotomous, branches linear, compressed (1–4 mm broad) or subterete, branch apices with a thickened cap; cystocarps with thick-walled sterile gonimoblast tissue


3. Branching irregular, branches flat, varying in width (4–50 mm broad), branch apices without a thickened cap; cystocarps lacking thick-walled sterile gonimoblast tissue


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