Of Cochlearia officinalis L. and C. anglica L. 160 herbarium specimens with well developed basal and cauline leaves, and with flowers or mature fruits, all collected in the Netherlands, have been investigated. Fig. 1, j shows a theoretical frequency distribution curve of a single character for two well distinguishable species in general. Fig. 1, a-g show the frequency distribution curves of the measured characters of the species under discussion: a. angle of attachment of the lamina to the petiole in the basal leaves (explained in fig. 1, h and i for C. officinalis and C. anglica respectively); b. length-breadth relation of basal leaves; c. id. of stem leaves; d. length of petals; e. length of style; f. length-breadth relation of septum, and g. length of seed. It is concluded that the greater part of the curves do not show the double top of fig. 1, j, and that therefore the two species cannot be distinguished very easily. Only characters a and f have two tops. The average of character f for C. anglica differs from that given in most floras. Fig. 2, a-f and table I show the results of measurements on selected herbarium specimens, the selection being based on the habitat. “Officinalis” specimens found in brackish bank vegetations of the alliance Senecion fluviatilis (transition to Agropyro-Rumicion) were separated from “anglica” ones, originating from salt marsh vegetations of the alliance Armerion maritimae. It now appeared that there exists a rather close connection between morphology and ecology in Cochlearia, since most of the curves are symmetrical; averages differ considerably in most cases (numbers between brackets are standard deviations of observations and average respectively). Separation of the two species, provided that the plants are collected in “pure” habitats, appears to be possible; however, in those cases where difficulties in identification are met with, population study will be necessary.