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Electronic Flora of South Australia Genus Fact Sheet
Phylum Rhodophyta – Class Florideophyceae – Order Gigartinales – Family Nemastomataceae
Thallus erect, subdichotomous, branches more or less linear, slightly compressed, drying cartilaginous. Structure multiaxial, with a cortex of branched filaments (with pyriform gland cells) lacking secondary pit-connections between the cells of adjacent filaments; medulla of entangled filaments; occasional uniseriate rhizoidal filaments present.
Reproduction: Sexual thalli dioecious. Carpogonial branches of 3–4 cells, connecting filaments issuing from the fertilized carpogonium, simple but becoming branched. Auxiliary cell subterminal in an unbranched rhizoidal filament, clear before fertilization. Gonimoblast initial arising from connecting filament adjacent to its point of fusion to the auxiliary cell, developing mainly thallus-inwardly, all cells becoming carposporangia; connecting filament continuing growth to other auxiliary cells. Pericarp and ostiole absent. Spermatangia cut off from outer cortical cells near branch tips.
Tetrasporangia unknown.
Type (and only) species: A. corneus (J. Agardh) Kraft, comb. nov.
Taxonomic notes: Adelophyton Kraft 1975: 280, figs 1–22, non Adelophyton Renault 1901: 424.
Adelophycus is closest in anatomy to the type species of the genus Nemastoma, N. dichotomum. In both, the fronds are cartilaginous, the cortex is compact and with prominent gland cells, and the auxiliary cell is intercalary toward the distal end of an unbranched rhizoid that bends outward from the medulla and terminates in the cortex. The clear illustrations of Berthold (1884, pl. 6 figs 9–15) depicting these features have been long overlooked but are confirmed by Athanasiadis (1988) and Robins (pers. comm.). Most, if not all, species of Nemastoma other than the type may need to be transferred to other genera.
Nemastoma dichotomum differs from Adelophycus primarily in its carpogonial branches, which are restricted to supporting cells that are intercalary in rhizoids. In Adelophycus, in contrast, supporting cells are intercalary within normal pseudodichotomous filaments of the cortex. Although they were illustrated by Berthold, Athanasiadis found no evidence of connecting filaments in N. dichotomum, the cystocarps being apparently the result of apomixis. Carposporophytes in N. dichotomum are globular and orientated outward, in contrast to those of Adelophycus which are wedge-shaped and orientated toward the thallus interior. A final difference lies in the rhizoids themselves, which are branched distally in N. dichotomum but are unbranched in Adelophycus.
References:
ATHANASIADIS, A. (1988). North Aegean Marine Algae H. Studies on the thallus structure and reproduction of Nemastoma dichotomum J. Agardh and Predaea ollivieri J. Feldmann (Rhodophyta, Gigartinales). Bot. Mar. 31, 23–32.
BERTHOLD, G. (1884). Cryptonemiaceen. Fauna and Flora des Golfes von Neapel. Monogr. XII. (Engelmann: Leipzig.)
KRAFT, G.T. (1975). Consideration of the order Cryptonemiales and the families Nemastomataceae and Furcellariaceae (Gigartinales, Rhodophyta) in light of the morphology of Adelophyton corneum (J. Agardh) gen. et comb. nov. from southern Australia. Br. phycol. J. 10, 279–290.
RENAULT, B. (1901). Sur un nouveau genre de tige fossile. Bull. Soc. Hist. nat. Autun. 13, 405–424, Plates 6–10.
The Marine Benthic Flora of Southern Australia Part IIIA complete list of references.
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.
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