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Abstract: Clover and Jotter described 1941 already E. decumbens from the Marble Canyon on the Colorado River. In the newer literature L. Benson was the only one, who took initially note of this taxa when he combined „E. engelmannii var. decumbens”. Only when Blum et al. (1998) combined in their monograph Echinocereus this taxa as E. engelmannii subsp. decumbens and classified some parts of „variegatus”, this taxon came to attention.
E. Lutz verified the herbarium sheet of the holotype in the herbarium of the University of Michigan (MICH) and led to the conclusion, that this plant did not belong to E. engelmannii. After that, several Echinocereus specialists (E. Lutz, W. Hodgson, D. Felix and for sure some others) tried unsuccessful to discover similar plants close to the original habitat. Some followed to the indication „Mile 16,5” of the Colorado River, which turned out as wrong. Until today discussions are ongoing, in order to solve the open issues.
The authors are concerned with this issue and they tried based on literature- herbarium- and own field studies, to come finally to a conclusion with this open subject. All in all it can be said, that a clarification of E. decumbens is impossible for now. In this case the taxon E. decumbens is perhaps either a hybrid between E. canyonensis x E. engelmannii, or a solitary specimen of E. canyonensis, or a varying form of E. engelmannii from this large distribution area (the option, which the authors prefer).
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