Electronic Flora of South Australia Family Fact Sheet

FAMILY ARESCHOUGIACEAE J. Agardh 1876: 246,273

Phylum Rhodophyta – Class Florideophyceae – Order Gigartinales

Thallus usually erect, branches terete to compressed or foliose, a few genera parasitic and pulvinate. Structure uniaxial or multiaxial, usually with a medulla of entangled filaments (sometimes surrounding an axial filament) and a pseudoparenchymatous cortex, the larger inner cells of which are multinucleate with secondary pit-connections.

Reproduction: Sexual thalli monoecious or dioecious; procarpic or non-procarpic. Carpogonial branches 3-celled, orientated inwards (or sideways) with a reflexed (or straight) trichogyne; connecting filaments single or several from each fertilized carpogonium (or absent), unbranched and non-septate, each diploidizing only a single auxiliary cell (an inner cortical cell, recognisable or not before contact), following which adjacent cells cut off slender filaments forming slight to distinct enveloping tissue (absent in Melanema) around the developing carposporophyte. Gonimoblast initials single or many, first orientated thallus inwards (lateral or outwards in some) but becoming radial, developing either a large central fusion cell or a placenta of partly fused vegetative and gonimoblast cells, then giving rise to radiating, branched gonimoblasts terminating in single, catenate or clustered carposporangia. Cystocarps largely immersed in, or often swelling, the branches, usually with a cortical pericarp, ostiolate. Spermatangia cut off from cortical cells, scattered or in sori.

Tetrasporangia scattered in the outer cortex, basally or laterally attached, zonately divided.

Life history triphasic with isomorphic gametophytes and tetrasporophytes.

Taxonomic notes: A family of some 22 genera. The multiaxial family Solieriaceae and the uniaxial Rhabdoniaceae have been combined (Gabrielson & Hommersand 1982a) because of their reproductive similarities (see also Gabrielson & Kraft 1984, p. 248), and Gabrielson &

Hommersand (1982a, b) recognise 3 tribes based on the number of connecting filaments, presence or not of sterile cells on the carpogonial branches, presence or not of an involucre or enveloping tissue around the carposporophyte, and position of the pit-connection to the tetrasporangium. Kraft & Gabrielson (1983, p. 56) however, in describing the parasitic genus Tikvahiella, discuss difficulties in clear separation of these tribes. Melanema (see below) differs from other genera in several aspects of reproduction and may not belong in this family.

Several authors have considered the uniaxial or multiaxial thallus difference inadequate to separate the Solieriaceae and Rhabdoniaceae, and Gabrielson & Garbary (1986, p. 343) claim that several genera can appear" uniaxial or multiaxial. The genera mentioned however are clearly defined near their apices and only appear multiaxial because the single axial filament does not persist in older parts. The uniaxial/multiaxial separation is hence used in the key below since it is a fairly conspicuous vegetative character always present.

The family name Areschougiaceae J. Agardh (1876, pp. 246, 273) was earlier in the same publication as Solieriaceae (J. Agardh 1876, p. 597). The latter (including Caulacanthus) was initially a superfluous synonym of Caulacanthaceae Kützing (1843, p. 389) - see Silva (1980, p. 86) - hence Areschougiaceae is here used (Kraft, pers. comm.).

References:

AGARDH, J.G. (1876). Species Genera et Ordines Algarum. Vol. 3, Part 1 - Epicrisis systematis Floridearum, pp. i-vii, 1–724. (Weigel: Leipzig.)

GABRIELSON, P.W. & GARBARY, D. (1986). Systematics of red algae (Rhodophyta). CRC Critical Reviews in Plant Sciences, Vol. 3, Issue 4, pp. 325–366.

GABRIELSON, P.W. & HOMMERSAND, M.H. (1982a). The Atlantic species of Solieria (Gigartinales, Rhodophyta): their morphology, distribution and affinities. J. Phycol. 18, 31–45.

GABRIELSON, P.W. & KRAFT, G.T. (1984). The Marine Algae of Lord Howe Island (N.S.W.): the Family Solieriaceae (Gigartinales, Rhodophyta). Brunonia 7, 217–251.

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

KRAFT, G.T. & GABRIELSON, P.W. (1983). Tikvahiella candida gen. et sp. nov. (Solieriaceae, Rhodophyta), a new adelphoparasite from southern Australia. Phycologia 22, 47–57.

SILVA, P.C. (1980). Names of classes and families of living algae. Regnum vegetabile 103, 1–156.

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

Author: H.B.S. Womersley

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 GENERA OF ARESCHOUGIACEAE

1. Apices multiaxial, thallus erect and branched or pulvinate and parasitic

2

1. Apices uniaxial, axial filament persistent or not, thallus erect and branched

5

2. Thallus pulvinate, lobed, 3–6 mm high, parasitic on Solieria robusta

TIKVAHIELLA

2. Thallus erect, 2–30 (–40) cm high, branches terete or compressed

3

3. Thallus complanately branched, branches compressed, firm, with a medulla of longitudinal filaments and a moderately broad pseudoparenchymatous cortex

CALLOPHYCUS

3. Thallus branches terete, soft or firm, with a broad, laxly filamentous medulla or a narrow medulla of longitudinal filaments

4

4. Thallus relatively soft, irregularly branched; medulla broad, of lax entangled filaments; enveloping tissue around the carposporophyte prominent

SOLIERIA

4. Thallus firm, subdichotomously branched; medulla narrow, of compact longitudinal filaments, with a broad pseudoparenchymatous cortex; enveloping tissue around the carposporophyte absent

SARCONEMA

5. Central axial filament clear only near branch apices; nutritive tissue absent adjacent to diploidized auxiliary cell

RHABDONIA

5. Central axial filament clear throughout thallus; nutritive tissue present adjacent to diploidized auxiliary cell

6

6. Axial cells each with two periaxial cells at about 90°, alternating on successive cells; thallus branches constricted into elongate-ovoid segments, at least in younger parts

ERYTHROCLONIUM

6. Axial cells each with one periaxial cell; thallus branches terete to slightly compressed, not constricted into segments

7

7. Thallus branches terete to slightly compressed, 0.3–2 (–4) mm in diameter or broad; reproduction non-procarpic

ARESCHOUGIA

7. Thallus branches terete, upper branchlets less than 0.3 mm in diameter; reproduction procarpic

MELANEMA


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