Electronic Flora of South Australia Genus Fact Sheet

Genus PTEROCLADIA J. Agardh 1851: xi; 1852: 482

Phylum Rhodophyta – Class Florideophyceae – Order Gelidiales – Family Gelidiaceae

Thallus 5–30 cm long, cartilaginous, complanately and more or less pinnately branched, branches compressed to flat, often with basal stolons, attached by fibrous holdfasts. Structure uniaxial, with a more or less conspicuous apical cell, differentiating into a medulla of numerous longitudinal filaments and a compact cortex 2–6 cells thick of ovoid cells, smaller outwardly, each with several small rhodoplasts; rhizines usually abundant throughout the medulla.

Reproduction: Carpogonia sessile on inner cortical cells, arising near branch apices, accompanied by short filaments of small nutritive cells; carposporophyte developing on one side only of the basal placenta and the cystocarps thus unilocular (or with unequal locules in P. capillacea), with a single (rarely more) ostiole on one side only of the swollen pericarp; carposporangia in short chains. Spermatangial initials formed in patches near ends of lateral leaflets, cut off from outer cortical cells, producing ovoid spermatangia.

Tetrasporangia scattered (or in some species in regular rows) in ultimate leaflets of branches, cut off laterally from cortical cells and when mature lying in the inner cortex or outer medulla, usually decussately cruciately divided.

Life history triphasic with isomorphic tetrasporophytes and gametophytes, the latter usually dioecious.

Type species: P. lucida (Turner) J. Agardh 1852: 483.

Taxonomic notes: A genus of numerous described species [several of which have been placed under P. capillacea by Stewart (1968, p. 83)1, distinguished from Gelidium by the unilocular cystocarp usually with a single ostiole. A new genus and species, Pterocladiastrum robustum Akatsuka (1986a), has been distinguished from New Zealand forms of P. lucida; this taxon is discussed below under P. lucida and rejected.

Santelices (1991) clarified the differences in cystocarp structure between P. capillacea and P. lucida, suggesting that these two species probably differ generically, the former having a central placenta separating two unequal locules whereas in the latter the placenta is attached to the bottom of the cystocarp with only a single locule.

Norris (1992a) considered that separation of Pterocladia from Gelidium was not justified.

References:

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

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

AKATSUKA, I. (1986a). Pterocladiastrum, a new genus segregated from Pterocladia (Gélidiales, Rhodophyta). Bot. Mar. 29, 51–58.

NORRIS, R.E. (1992a). A proposed phylogenetic scheme for the Gélidiales. In Abbott, I.A. (Ed.), Taxonomy of Economic Seaweeds. With reference to some Pacific and Western Atlantic species. Vol. III, pp. 151–171. (Calif. Sea Grant College Program: La Jolla, Calif.)

SANTELICES, B. (1991). Variations in Cystocarp Structure in Pterocladia (Gélidiales: Rhodophyta). Pacific Sci. 45, 1–11.

STEWART, J.G. (1968). Morphological variation in Pterocladia pyramidale. J. Phycol. 4, 76–84.

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

Author: H.B.S. Womersley & M.D. Guiry

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 SPECIES OF PTEROCLADIA

1. Thallus irregularly pinnate, axes 3–4 mm broad in mid thallus, pinnae and pinnules usually 2–5 mm apart, pinnae usually more than 2 mm broad; reproductive organs in compressed pinnules

P. lucida

1. Thallus regularly pinnate, axes 0.6–2.5 mm broad, pinnae and pinnules more or less linear, less than 2 mm broad, often 1–2 mm apart (becoming more in P. capillacea); reproductive organs in slightly compressed pinnules or subterete ramuli fringing the pinnules

2

2. Axes relatively thin, pinnae 2–5 (–10) mm apart, reproductive organs in compressed pinnules

P. capillacea

2. . Axes relatively thick, pinnae and pinnules close set, positioned almost at right angles, 0.5–1 mm apart, reproductive organs in subterete ramuli fringing the pinnules

P. rectangularis


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