Helianthemum Canum (L) Baumg und seine nächsten Verwandten

    Abstract

    Helianthemum canuum is highly variable species, and therefore one for which it is difficult to define the limits. In the volume of Engler's “Pflanzenreich,” dealing with thj Cistaceæ, Dr. W. Grosser differentiates two varieties that are each again subdivided into Several forms. The herbarium worker may follow such a splitting of interrelated forms, but it is extremely unlikely that he could separate them in the field where intermediate forms would probably be found. Dr. Janchen puts forward an alternative limitation of Helianthemum canum, and one or two nearly related species. Broadly, he merges in canum part of the species recognised by Grosser as marifolium, and maintains italicum and rupifragum as independent species. There appears to be considerable support for Janchen's arrangement, and the adoption by Grosser of two varieties under different species as H. canum v. marifolium and H. marifolium v. canum is decidedly confusing, but the determinations of Dr. Janchen are also based solely on herbarium material, although a crucial test could be obtained either by a study of the plants as they grow or by cultivating them from seed. Undoubtedly, such methods are arduous but not impossible, as all the plants under discussion are European. It is only right to add that Dr. Janchen himself recognises the necessity for determining the systematic limits in such variable species by the methods indicated.

    Helianthemum Canum (L) Baumg. und seine nächsten Verwandten.

    By Dr. E. Janchen. Pp. 68. (Jena: Gustav Fischer, 1907.) Price 2.50 marks.

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