Original paper

The Staurastrum tohopekaligense species cluster

Ling, H.U.; Tyler, Peter A.

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Algological Studies/Archiv für Hydrobiologie, Supplement Volumes No. 76 (1995), p. 27 - 60

85 references

published: Feb 27, 1995

DOI: 10.1127/algol_stud/76/1995/27

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Abstract

A survey of desmid populations from tropical Australia revealed a complex, polymorphic group of taxa centred morphologically on Staurastrum tohopekaligense. The cells in the populations can be divided into three main groups defined by the number of processes, 6, 9 or 15, adorning each semicell. The 6-arm cells can be identified with S. clevei, the small and large 9-arm cells with S. furcatum and S. tohopekaligense respectively, the smaller 15-arm cells with S. leptacanthum and the larger ones with S. arctiscon var. glabrum, all with considerable overlap and confusion. Further studies of the populations, as well as populations from other parts of Australia and overseas, demonstrated a broader morphological spectrum, including rare 3 and 12-arm forms, with a continuous range of size intergradation and dichotypical linkages through the S. clevei - furcatum - tohopekaligense - leptacanthum - arctiscon var. glabrum axis. Basic triradiate symmetry in this series is determined by three structure radii, where a simple stepwise placement of 1, 2, 3, 4 or 5 processes at each structure radius determines the 3, 6, 9, 12 or 15-arm morphology. Depending on circumstances, morphogenetic expression may result in the 3, 6, 9, 12 or 15-arm morphology or, in any one habitat, a mixture of all five or them, including dichotypical forms. The greatest range of morphological variability was encountered in seasonally-variable, shallow, tropical water bodies whereas in deep, stable, physicochemically-benign lakes only a narrow range of variation was exhibited. We interpret this to be the influence of environmental variation on morphogenesis.

Keywords

Desmids • Staurastrum • morphological variability • morphogenesis • dichotypy • taxonomic intergradation