Electronic Flora of South Australia Genus Fact Sheet
Phylum Rhodophyta – Order Ceramiales – Family Ceramiaceae – Tribe Callithamnieae
Thallus erect, 1–20 cm high, much branched with indeterminate axes and main branches clothed with ecorticate, usually determinate, alternately branched branchlets, some continuing growth as indeterminate branches; branches becoming corticate by appressed rhizoidal filaments from the basal cells of ecorticate branchlets, becoming dense and often 2–4 cells thick below, with the outer cells producing short, simple or slightly branched, anticlinal filaments forming a sparse to dense hirsute tomentum over the older branches. Gland cells absent. Cells uninucleate, often with further darkly staining globules.
Reproduction: Gametophytes dioecious. Procarps formed on cells of ecorticate branchlets, with two periaxial cells, one (the supporting cell) producing a 4-celled carpogonial branch with the first 3 cells horizontal around the supporting cell and the carpogonium and trichogyne directed upwards. Post-fertilization the carpogonium usually divides longitudinally and each cell unites via a small connecting cell with the two auxiliary cells cut off the supporting cell and the other periaxial cell. A gonimoblast initial then produces lobes of carposporangia which may be rounded or conical and furcate one or more times. Species are without or with an involucre of curved, simple or branched branchlets arising from the cell below the procarp. Spermatangial clusters single on cells of ecorticate branchlets, with a single, elongate, anticlinal stalk cell producing several initials which, directly or via further cells, produce terminal spermatangia.
Tetrasporangia produced singly on cells of ecorticate branchlets, sessile, subspherical, tetrahedrally divided.
Type species: H. mucronata Wollaston & Womersley, sp. nov.
Taxonomic notes: Hirsutithallia is named from the hirsute tomentum of anticlinal filaments, borne on the outer layer of rhizoidal filaments clothing the older axes and branches. While some species of Callithamnion have older branches corticated, the cortical filaments are usually much looser and do not produce the striking tomentum of anticlinal filaments characteristic of Hirsutithallia. Development of the procarp and carposporophyte are very similar to Callithamnion (and Aglaothamnion if accepted), but the uninucleate cells would ally Hirsutithallia with Aglaothamnion. The spermatangial clusters, with a distinctly elongate stalk cell bearing a hemispherical cushion of initials and ultimate spermatangia, also appear distinctive for Hirsutithallia and different to Callithamnion where more than one spermatangial branch arises from each thallus cell and a prominent, elongate, stalk cell does not occur.
However, two species (H. formosa and H. angustata), while similar to the other species in cortex characteristics and carposporophyte development, differ in having involucres around the carposporophytes and the spermatangial branches are similar to those in Callithamnion. While currently placed in Hirsutithallia, their position merits further study.
References: The Marine Benthic Flora of Southern Australia Part IIIC
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 SPECIES OF HIRSUTITHALLIA
1. Cortication commencing close to apices. Carposporophytes without an involucre of filaments from the cell below the procarp.
1. Cortication starting some distance from apices. Carposporophytes with an involucre of curved filaments from the cell below the procarp
2. Terminal cells of branchlets, especially their walls, mucronate
2. Terminal cells of branchlets with rounded ends and walls
3. Determinate branchlets
3. Determinate branchlets
4. Anticlinal cortical filaments profuse, often with 2 from each cell of the longitudinal cortical filaments; determinate branchlets radially branched, basal cells
4. Anticlinal cortical filaments sparse to abundant, usually with only one from each longitudinal cortical cell; determinate branchlets mostly abaxially branched, basal cells
5. Thallus moderately robust, branching often subdistichous, axial cells L/D
5. Thallus slender, branching irregularly radial, axial cells of corticated branches L/D
State Herbarium of South Australia