Electronic Flora of South Australia Family Fact Sheet

FAMILY DASYACEAE Kützing 1843: 413, 414

Phylum Rhodophyta – Order Ceramiales

Thallus erect, terete or compressed, much branched radially, bilaterally, or dorsiventrally, with sympodial apices producing axes with 4–11 pericentral cells and monosiphonous (or basally polysiphonous), branched, rhodoplastic, pseudolateral filaments (with laterally adherent basal walls to the upper cells of the branch subdichotomies) developed from the displaced apical cells of the sympodium; pseudolaterals free or forming a network; adventitious monosiphonous filaments present in some species; pericentral cells produced in a circular or alternating sequence, in some species dividing transversely; axes ecorticate or corticate by compact rhizoids. Holdfast rhizoidal, compact.

Reproduction: Gametophytes dioecious. Procarps borne on lower pseudolateral cells, with 5 pericentral cells cut off in circular or alternating sequence, one being the supporting cell of a 4-celled carpogonial branch, and with 2 groups of sterile cells which usually divide further after fertilization. Fertilized carpogonium producing 1 or 2 connecting cells, one fusing with the auxiliary cell, followed by the auxiliary cell, central segment cell, and other cells forming a fusion cell; gonimoblast filaments producing carposporangia in rows or terminally with further carposporangia developing from below. Cystocarps globular to urceolate; pericarp of adherent corticated filaments, ostiolate, with initials present or absent at fertilization. Spermatangia formed on branches of pseudolaterals, with 4–5 pericentral cells dividing to form a layer of initials which cut off spermatangia over the surface of the cylindrical to lanceoid male organs.

Tetrasporangia occur in simple stichidia (branched in Thuretia) borne on cells of the pseudolaterals, with 4–10 pericentral cells cut off in alternating sequence, with 2–4 pre- or post-sporangial cover cells and whorls of 4–6 subspherical sporangia, tetrahedrally divided.

The Dasyaceae include some 12 or 13 genera (de Jong et al. 1997, p. 422), of which only Dasya C. Agardh, Heterosiphonia Montagne, Thuretia Decaisne and Colacodasya Schmitz occur on southern Australian coasts. Of these 4 genera, the first 3 are richly represented in this region. Millar (1996) discusses the validity of several of the other genera.

Some authors (e.g. de Jong et al. (1997) include Halodictyon Zanardini in the Dasyaceae, but this genus lacks vegetative pericentral cells, growth is not sympodial, and the spermatangial branches and stichidia are not dasyaceous; it is more likely to be an unusual member of the Rhodomelaceae.

A feature of all Dasyaceae appears to be the adherence of the lower walls of the upper cells of the subdichotomies of the pseudolaterals, and in most species the sterile cells and adjacent pericentral cells of the procarp become darkly staining and may be nutrtitive in function.

Life history triphasic with isomorphic gametophytes and tetrasporophytes; or apomeiotic.

References:

DE JONG, Y.S.D.M., PRUD'HOMME VAN REINE, W.F. & LOKHORST, G.M. (1997). Studies on Dasyaceae II. A revision of the genera Eupogodon and Dipterocladia gen. nov. (Ceramiales, Rhodophyta). Bot. Mar 40, 421–450.

KÜTZING, F.T. (1843). Phycologia generalis. (Leipzig.)

MILLAR, A.J.K. (1996). Dasya roslyniae sp. nov. (Dasyaceae, Rhodophyta) with a discussion on generic distinctions among Dasya, Eupogodon, Rhodoptilum, and Pogonophorella. J. Phycol. 32, 145–157.

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

Author: H.B.S. Womersley

Publication: Womersley, H.B.S. (24 December, 1998)
The Marine Benthic Flora of Southern Australia
Rhodophyta. Part IIIC. Ceramiales – Ceramiaceae, Dasyaceae
©State Herbarium of South Australia, Government of South Australia

KEY TO GENERA OF DASYACEAE

1. Thallus erect, monosiphonous filaments free, subdichotomous, not forming a network

2

1. Thallus erect, terete or flat, with monosiphonous filaments united to form a network, or pulvinate to globose, 2–5 mm across, parasitic on Dasya clavigera

  3

2. Thallus radially branched, occasionally with somewhat bilateral branches; pseudolaterals usually on every segment (two segments apart in a few species); 5 (rarely 4) vegetative pericentral cells; procarp without surrounding pericarp initials; stichidia with whorls of 4–7 tetrasporangia and 3 (2–4) post-sporangial cover cells;

DASYA

2. Thallus bilaterally branched; pseudolaterals borne alternately 2 or more axial segments apart; 4 or 7–13 pericentral cells; procarp with surrounding pericarp initials; stichidia with whorls of 4–9 tetrasporangia and 2 pre-sporangial cover cells, each dividing transversely

HETEROSIPHONIA

3. Monosiphonous filaments attached to form a network, thallus terete or compressed, with a central polysiphonous axis

THURETIA

3. Thallus pulvinate to globose, 2–5 mm across, parasitic on Dasya

COLACODASYA


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