Amphithallia, a genus with four-celled carpogonial branches and connecting filaments in the Corallinales (Rhodophyta)

ABSTRACT

The South African marine alga Amphithallia crassiuscula, previously subsumed in the widely reported Synarthrophyton patena, is here re-described as a distinct species and genus. Thalli grow as obligate epiphytes on Gelidium capense in the upper sublittoral zone (while S. patena grows on Ballia callitricha). Gametophytes are monoecious with four-celled carpogonial branches and sterile cells are borne on supporting cells (dioecious or hermaphroditic with two or three-celled carpogonial branches and sterile cells borne on hypogynous cells in Synarthrophyton). Postfertilization stages involve a connecting filament linking the carpogonium to several putative auxiliary cells, demonstrating a non-procarpic condition with apparent absence of a fusion cell. Gonimoblast filaments develop at the level of basal cells of carpogonial branches. Spermatangial mother cells remain either unbranched (cutting off spermatangia only) or develop dendroid (branched) filaments with terminal spermatangia (as in Synarthrophyton). Multiporate conceptacles develop straight pore canals lined by non-differentiated cells (conical canals with differentiated pore cells along the base in Synarthrophyton). The here described pre- and post-fertilization characters are new for the order Corallinales motivating the establishment of the new genus Amphithallia.

KEYWORDS:

• Hypogynous cell
• sterile cells
• pore cells
• Synarthrophyton schielianum
• supporting cells

SUBJECT EDITOR:

• Audrey Geffen

Acknowledgements

Sincere thanks are due to the keepers of the herbaria BM, L, LD, MEL, S, TCD, WELT, and UC, for information and/or sending materials on loan including types. The late Dr Yvonne M. Chamberlain generously shared materials of her S. African herbarium and discussed the taxonomy of Mesophyllum with the author at the Marine Laboratory of Portsmouth Polytechnic in October of 2008. Several referees and the editors made helpful comments and corrections on the present and previous versions of this paper. To those who advocate molecular and morphological-anatomical investigations to be combined, I remind that different data sets need to be worked out independently to increase their explanatory power (Athanasiadis and Ballantine 2014). I also underline that herbarium collections of corallines have so far produced partial DNA, which necessitates extrapolation and comparison to fresh collections.

Disclosure statement

No potential conflict of interest was reported by the author.