Identification notes
Well-grown C. giganteum does not normally present any identification problems, with its large, much-branched stems said to resemble miniature Christmas trees. However, little-branched forms do occur and then it can be confused with Calliergon cordifolium. By far the best way to tell the two apart is by microscopical examination of alar cells. The alar cells of C. giganteum are strikingly enlarged and very strongly differentiated from the cells above. You can see this very clearly in some of the photographs below. In C. cordifolium the cells are not as large and only weakly differentiated from the cells above.
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