Subfamily and generic descriptions: Lithophylloideae

Lithophylloideae

(Setchell 1943: 134 - as ‘Lithophylleae’)

Thallus non-geniculate; some but not all cells of contiguous vegetative filaments normally joined by secondary pit connections; cell fusions apparently absent or comparatively rare; tetrasporangia/ bisporangia lacking apical plugs and borne within uniporate conceptacles.

Ezo

• Plants nongeniculate and largely epigenous;
• Forming small, applanate, crustose thalli that lack protuberances;
• Anchored to the substratum (species of Lithophyllum) by cell adhesion, and by haustoria which penetrate the host surface layers and become appressed to or fuse with cells of the host;
• Thalli dorsiventral and dimerous;
• Basal filaments composed primarily of non-palisade cells;
• Epithallial cells, when present, with outermost walls rounded or flattened, but not flared;
• cells of adjacent filaments joined by secondary pit connections, cell fusions unknown;
• tetrasporangial conceptacles uniporate;
• tetrasporangia lacking apical plugs

COMMENTS: Adey et al. included the absence of plastids and pigmentation as a diagnostic character, but Woelkerling (1988) concluded that further studies are needed to confirm this. Ezo is similar to Lithophyllum, but for the possession of haustoria.
ETYMOLOGY: Ezo after the old name for Hokkaido, the type locality.

Lithophyllum

• Thallus non-geniculate, non-endophytic, and lacking haustoria;
• thallus dimerous, posessing a basal layer of cells that are predominately non-palisade;
• thallus lacking areas that are bistratose (consisting of basal cell and epithallial cell)
• spermatangial systems confined to the floor of the male conceptacle.

COMMENTS: (after Chamberlain 1991, Woelkerling 1988). Lithophyllum is distinguished from Titanoderma on the basis of:

• the possession of a basal layer consisting predominately of non-palisade cells, and
• no areas of bistratose thallus are present, as the thallus begins to thicken immediately behind the primary meristematic cell.

See Titanoderma for further details.
ETYMOLOGY: from the Greek lithos (stone) and the latinized Greek word phyllon (leaf).

Titanoderma

• Thallus non-geniculate, non-endophytic, and lacking haustoria;
• thallus dimerous, posessing a basal layer of predominately palisade cells throughout, except sometimes near the margin;
• thallus partly to entirely bistratose (consisting of basal cell and epithallial cell)--- [thicker species have bistratose margins];
• cells of adjacent filaments joined by secondary pit connections, cell fusions unknown;
• spermatangial systems confined to the floor of the male conceptacle.

(after Chamberlain 1991, Woelkerling 1988).

COMMENTS: Titanoderma is distinguished from Lithophyllum on the basis of:

• the possession of a basal layer consisting predominately of palisade cells, and

• at least some areas of bistratose thallus are present, usually at the margin in thicker species.

Campbell and Woelkerling (1990) and Woelkerling and Campbell (1992) did not consider Titanoderma to be distinguishable from Lithophyllum because palisade and non-palisade cells as well as bistratose and non-bistratose margins can occur together in the same thallus to varying degrees. In southern Africa, the tropical Indo-Pacific and other areas where I have examined specimens, no difficulty was found in assigning species to Titanoderma or Lithophyllum on the basis of the two characters noted above. The genera would appear to be much more difficult to distinguish in Australia (Campbell and Woelkerling 1990, and Woelkerling and Campbell 1992), further work is necessary to determine with certainty whether Titanoderma and Lithophyllum should really be considered congeneric. In this treatment, I have therefore chosen to use the generic concepts of Lithophyllum and Titanoderma as in Chamberlain (1991) until such time as genetic studies can be conducted to evaluate this controversy more fully.
ETYMOLOGY: from the Greek mythological Titan and derma skin.

Tenarea

• Thallus non-geniculate, non-endophytic, and lacking haustoria;
• Plants consist of thin, branched, intertwined and interlocked, taeniform lamellae forming variously shaped tahlli and lackign protubberances;
• thallus dimerous, and isobilaterally organised, possessing basal that are composed oc cells which are predominately palisade and form two central rows;
• cells of adjacent filaments joined by secondary pit connections, cell fusions unknown;
• tetrasporangial conceptacles uniporate;
• tetrasporangia lacking apical plugs

Tenarea is organised like two Titanoderma thalli growing back-to-back, and indeed some phycologists believe that it is congeneric with Titanoderma. Should that be the case, Tenarea is the older name and would take precidence over Titanoderma as the correct name for the genus. However, further studies are needed to determine whether this is indeed the case.

Back to family/subfamily page

Back to coralline page

Derek Keats,
updated 03/09/01