Electronic Flora of South Australia Genus Fact Sheet

Genus HETEROSIPHONIA Montagne 1842: 4, nom. cons.

Phylum Rhodophyta – Order Ceramiales – Family Dasyaceae

Thallus erect from a discoid holdfast or prostrate axes. Axes sympodially developed and alternately distichously branched, terete or occasionally compressed, ecorticate or corticated by compact rhizoidal filaments, with pseudolaterals and lateral branches arising 2–9 segments apart. Structure. Axes with 4 or 7–13 pericentral cells cut off in alternating sequence. Pseudolaterals monosiphonous or becoming basally polysiphonous, persistent, subdichotomous once to several times, with adherent lower walls at the subdichotomies, rhodoplastic; adventitious monosiphonous filaments may arise from cortical cells.

Reproduction: Gametophytes dioecious. Procarps occur on segments subtending the subdichotomies of the pseudolaterals, with a supporting cell bearing a 4-celled carpogonial branch and 2 groups of sterile cells, the supporting cell being the fifth and last formed pericentral cell of the fertile segment; the sterile pericentral cells divide before fertilization to form the pericarp initials. Post-fertilization, fusion between the carpogonium and auxiliary cell occurs via a connecting cell, and the fusion cell involves the auxiliary cell, residual supporting cell, adjacent pericentral cells and lower gonimoblast cells. Carposporangia occur in rows or terminally on the much branched gonimoblast. Cystocarps have an urceolate pericarp, with or without a prominent neck. Spermatangial branches occur as branches of the pseudolaterals, elongate lanceoid, with 4 or 5 pericentral cells cut off in alternating sequence, dividing to form an outer surface layer of spermatangia.

Tetrasporangial stichidia occur as branches of the pseudolaterals, sessile or with monosiphonous or polysiphonous stalks, with 4–9 pericentral cells formed in alternating sequence, dividing to produce 2 pre-sporangial cover cells and then a tetrasporangium; the cover cells divide once horizontally to form 4 cells which completely cover the mature sporangium, with 4–9 sporangia in each segment.

Type species: H. berkeleyi Montagne 1842: 4.

Taxonomic notes: A genus of numerous species, widely distributed.

Heterosiphonia differs from Dasya in having thalli always bilaterally (distichously) branched, 4 or 7–13 pericentral cells per segment, pseudolaterals borne 2 or more axial segments apart, pre-fertilization pericarp initials, and stichidia with whorls of 4–9 tetrasporangia and 2 pre-sporangial cover cells, each dividing transversely and covering the sporangium.

Certain species of Dasya show some of the above features, as discussed above.

As well as the southern Australian species described below, H. multiceps (Harvey) Falkenberg (1901, p. 654) occurs on the western coast of Australia.

References:

FALKENBERG, P. (1901). Die Rhodomelaceen des Golfes von Neapel und der angrenzenden Meeres-abschnitte. Fauna und Flora des Golfes von Neapel. Monogr. 26. (Friedlander: Berlin.)

MONTAGNE, C. (1842) Troisieme centurie de plantes cellulaires exotiques nouvelles. Decades V, VI, VII, et VIII. Ann. Sci. Nat. Bot. Ser. 2, 18, 241–282, Plate 7.

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

Author: M.J. Parsons and 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 SPECIES OF HETEROSIPHONIA

1. Thallus ecorticate throughout.	2
1. Thallus corticate at least in the basal portions	5
2. Internodes of (2–) 4–7 segments between pseudolaterals; pseudolaterals polysiphonous except at branch ends	H. microcladioides
2. Internodes of 2 (–3) segments between the pseudolaterals; pseudolaterals monosiphonous except for basal polysiphonous segments	3
3. Thallus with 4 pericentral cells	H. callithamnium
3. Thallus with 7–11 pericentral cells	4
4. Thallus small, to 3 cm in length; axes 150–250 µm in diameter; 7–8 pericentral cells; epiphytic or epilithic	H. australis
4. Thallus larger, to 12 cm in length, axes (200–) 300–700 µm in diameter; 8–11 pericentral cells; usually epiphytic	H. wrangelioides
5. Pseudolaterals separated by 2 (–3) segments; basal corticated axes with short anticlinal filaments	6
5. Pseudolaterals separated by (3–) 4–7 segments; basal corticated axes without anticlinal filaments	7
6. Main axis of feather-like fronds corticate to apex; heavily corticated basal portion of axis with copious adventitious monosiphonous filaments	H. muelleri
6. Main axis of feather-like fronds ecorticate, arising from a corticate basal portion of the axis which has a light covering of adventitious filaments	H. crassipes
7. Ultimate branches of pseudolaterals monosiphonous, subulate, more than 85 µm in diameter; (12–) 13 pericentral cells	H. curdieana
7. Ultimate branches of pseudolaterals monosiphonous, usually tapering to a fine filament, occasionally subulate, less than 85 µm in diameter; 8–12 pericentral cells	8
8. Pseudolaterals consisting of ecorticate polysiphonous and monosiphonous filaments borne on a corticate sympodial axis; no thickened perennating basal axis, older axes in transverse section showing large and conspicuous pericentral cells around the axial cell	H. gunniana
8. Pseudolaterals consisting of corticate polysiphonous segments and ecorticate monosiphonous filaments; polysiphonous segments completely corticated in older plants which also have a thick perennating basal axis; older axes in transverse section with a large axial cell and pericentral cells inconspicuous in the rhizoidal cortex	H. lawrenciana

Email Contact:
State Herbarium of South Australia