Electronic Flora of South Australia Family Fact Sheet

FAMILY DICRANEMATACEAE Kylin 1932: 65

Phylum Rhodophyta – Class Florideophyceae – Order Gigartinales

Thallus erect or decumbent, subdichotomously and often complanately branched, adventitious laterals often present, branches terete to compressed or flat, cartilaginous, epiphytic or epilithic. Structure multiaxial, pseudoparenchymatous throughout or with a compact medulla of elongate cells; secondary pit-connections abundant between subsurface cortical cells, inner cells multinucleate.

Reproduction: Sexual thalli monoecious, procarpic or non-procarpic. Carpogonial branches 2- or 3-celled, borne singly on inner or mid cortical (supporting) cells and directed outwardly. Auxiliary cell either the supporting cell or an undifferentiated adjacent cortical cell distal to the supporting cell, diploidization by direct contact between carpogonium and auxiliary cell; fusion cell usually small, composed of the auxiliary cell and several partly fused adjacent cells, producing several radiating gonimoblast initials which develop either towards the branch centre, radially, or to the surface. Fusions of gonimoblast and vegetative cells form a placenta surmounted by the outer layer of the carposporophyte producing carposporangia singly or in short chains. Cystocarps slightly to largely protuberant, usually ostiolate, with a thick pericarp or covered only by the cortex. Spermatangia in sunken, isolated, clusters between outer cortical cells, terminal or catenate.

Tetrasporangia scattered in the outer cortex or in raised nemathecia, zonately divided.

The Dicranemataceae is a largely Australian family described in detail by Kraft (1977b). Norris (1987a) has suggested that the Dicranemataceae should be merged with the Sarcodiaceae. However, there are significant differences between these two families although the Sarcodiaceae (see Rasmussen 1964; Searles 1968, 1969; Norris 1987a; also pers. obs. of G.T. Kraft) is less well known than the Dicranemataceae, and it seems best to keep them separate though possibly related.

In the Sarcodiaceae, the carpogonial branch is 3-celled and curves laterally with the trichogyne usually reflexed, with a single outwardly directed gonimoblast initial; the placentation of the carposporophyte is narrow and basal, with downward growing nutritive filaments connecting the inner gonimoblast tissue to the gametophyte, forming a reticulate fusion cell region. In the Dicranemataceae, in contrast, the carpogonial branch of 2 or 3 cells is usually straight, and multiple gonimoblasts issue from the fusion cell inwardly, radially or laterally, with adjacent gametophyte cells becoming involved to form a reticulate base to the carposporophyte.

Life history triphasic with isomorphic gametophytes and tetrasporophytes.

Taxonomic notes: An important difference also lies in the arrangement of the spermatangia, which in the Sarcodiaceae occur in sori, being cut off in short chains from surface cortical cells near branch apices. In the Dicranemataceae the spermatangia occur in isolated sunken clusters or pits in the cortex. As well as in this family, spermatangia in such pits are consistent for the families Acrotylaceae, Mychodeaceae and Mychodeophyllaceae (Kraft 1977b) and appear to give a good family separation from taxa with surface son of spermatangia.

While details of reproductive development in the Sarcodiaceae are not yet adequately known, the two families are considered here to be sufficiently distinct to be treated separately.

References:

KRAFT, G.T. (1977b). Studies of marine algae in the lesser-known families of the Gigartinales (Rhodophyta). H. The Dicranemaceae. Aust. J. Bot. 25, 219–267.

KYLIN, H. (1932). Die Florideenordnung Gigartinales. Lunds Univ. Årsskr. N.F. Avd. 2, 28 (8), 1–88, Plates 1–28.

NORRIS, R.E. (1987a). Reproduction in Sarcodia dentata (Suhr) comb. nov. (Gigartinales, Rhodophyceae), with comments on the Sarcodiaceae. Br. phycol. J. 22, 147–155.

RASMUSSEN, R.A. (1964). The structure and reproduction of Sarcodia montagneana (Rhodophyta). Phycologia 4, 1–7.

SEARLES, R.B. (1968). Morphological studies of red algae of the order Gigartinales. Univ. Calif Pubis Bot. 43, vi + 1–86, Plates 1–12.

SEARLES, R.B. (1969). Observations on the morphology of Trematocarpus dichotomus Kützing and the status of the genus Dicurella. Phycologia 8, 21–25.

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 DICRANEMATACEAE

1. Thallus branches terete; carposporophyte basally attached, developing towards the branch centre, carposporangia obovoid, pericarp comprising the branch cortex; epiphytic on the sea-grass Amphibolis

  DICRANEMA

1. Thallus branches compressed or flat; carposporophyte basally attached but developing towards branch surface, carposporangia subspherical, pericarp thick, developed by cell proliferation; epilithic

2

2. Branches 2–3 mm broad, arising from stolons, erect; slender medulla of elongate cells present; cystocarps and spermatangia on the same blade surface, carposporophyte surface even, with peripheral cells bearing 1–3 carposporangia; cystocarps forming sub-terminal knobs

PELTASTA

2. Branches 5–12 mm broad, decumbent and basally attached by haptera arising from the under surface; cystocarps on the under surface, spermatangial clusters on the upper surface; periphery of mature carposporophyte undulate, with short columns of 1–2 cells bearing terminal carposporangia

TYLOTUS


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