Electronic Flora of South Australia Family Fact Sheet

ORDER DASYCLADALES Pascher

Phylum Chlorophyta

Thallus diplontic, coenocytic (often with constricted segments but end walls always perforate apart from plug formation), radially symmetrical with an erect axis bearing whorls of lateral branches which are simple or (usually) di- to polychotomously branched, free or with the ultimate segments united laterally to form an outer cortex; vegetative thallus usually at first with a single, giant nucleus in the rhizoidal base, becoming multinucleate later before cyst formation; cell wall of mannan; chloroplasts usually small, without a pyrenoid.

Reproduction: Reproduction by iso- or anisogmates formed in cysts (with a cellulose wall) or freely in gametangia borne on the lateral branches or as gametangial rays, becoming separated by a plug (Menzel 1980); position of meiosis not fully established, probably before or during fragmentation of the giant primary nucleus.

Taxonomic notes: This is a distinctive order with its radial symmetry, coenocytic structure, and presence in most genera of a single giant nucleus before reproductive cysts are formed. The best known genus, Acetabularia, has been used extensively in developmental biology (e.g. Woodcock 1977; Bonotto, Kefeli and Puiseux-Dao 1979). Some 9 living genera and over 50 fossil genera are recognised, the latter largely due to their superficial deposition of calcium carbonate on the distinctive whorled thallus.

Most authors have recognised a single family for the living genera, but Valet (1969, p. 577) recognises two families.

References:

BONOTTO, S., KEFELI, V. & PUISEUX-DAO, S. (Eds) (1979). Developmental Biology of Acetabularia. (Elsevier: Amsterdam.)

MENZEL, D. (1980). Plug formation and peroxidase accumulation in two orders of siphonous green algae (Caulerpales and Dasycladales) in relation to fertilization and injury. Phycologia 19, 37–48.

VALET, G. (1969). Contribution a l'étude des Dayscladales 2. Cytologie et reproduction. 3. Révision systématique. Nova Hedwigia 17, 551–644, Plates 133–162.

WOODCOCK, C.L.F. (Ed.) (1977). Progress in Acetabularia research. (Academic Press: New York.)

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

Author: H.B.S. Womersley

Publication: Womersley, H.B.S. (31 May, 1984)
The Marine Benthic Flora of Southern Australia
Part I
©Board of the Botanic Gardens and State Herbarium, Government of South Australia

KEY TO FAMILIES OF DASYCLADALES

1. Axes bearing whorls of laterals of only one type

DASYCLADACEAE

1. Axes bearing whorls of laterals of two types, alternating or with numerous whorls of slender, colourless hair-like laterals and a single summit whorl of green gametangial rays

POLYPHYSACEAE


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