The Taxonomy of Sphacelaria cirrosa (Roth.) Ag., Sphacelaria fusca (Huds.) Ag., and Sphacelaria furcigera (Kutz.) Sauv: A Simple Statistical Approach

An attempt has been made to apply some simple statistical techniquesto the taxonomy of a problematical group of species within thegenus Sphacelaria Lyngb. Measurements were carried out on materialcollected from the field, material made available from Herbariumcollections and on material grown under experimental conditionsThe main characteristics considered are cell and filament dimensions,although certain reproductive structures have also been measured. It has been found that the number of longitudinal divisionsin each segment of the main axes and the primary branches hasa profound effect on the over-all appearance of the fronds ofthe three species investigated. Segment length breadth ratioand frond stiffness have been shown to be dependent on the numberof longitudinal walls. This characteristic has enabled one ofthe species, S. cirrosa (Roth) Ag., to be readily distinguishedfrom the other two. Another factor shown to be important is the determinate patternof growth displayed by S. cirrosa as opposed to the indeterminatepattern displayed by S. fusca (Huds ) Ag. and S. furcigera (Kutz.)Sauv. The pattern of growth affects the number of longitudinalwalls, filament width, and the relative lengths of the primarybranches. The angle at which branches emanate from the main axes has beenshown to be a useful characteristic in this group of species. The variability in the number of arms produced by each propagulepresents an interesting problem which has only been described,experimental work suggesting no explanation for this phenomenon.The degree of variability is clearly different in each speciesand is useful taxonomically if a large enough sample is availablefor examination.