The Reliability of Cratoneuron Commutatum (Hewd.) Roth as an `Indicator Moss'

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Abstract
An investigation of the water chemistry of 41 flushes and springs, in 30 of which the aquatic moss Cratoneuron commutatum was present, has confirmed the view that this species is an indicator of base-rich conditions but with certain qualifications. Only C. commutatum var. commutatum consistently affects waters rich in Ca. The var. falcatum can tolerate waters much poorer in divalent ions. Evidence is presented that the presence of the var. falcatum in waters poor in Ca depends upon the ability of Mg to compensate to a certain extent for the deficiency of Ca. There is also evidence that where the concentration of Ca and Mg taken together are so low that they are hardly adequate for the occurrence of this variety, Na and K may in a similar manner compensate for the deficiency of the divalent ions. Little evidence was obtained of a relationship between the amount of Fe in the water and the presence or absence of C. commutatum, but there is a possibility that when the concentrations of Ca and Mg become limiting, a high concentration of Fe may inhibit the growth of the moss.