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Numerical analyses of hop (strobilus) samples showed that the geographical origin of cultivars of Humulus lupulus L. from North America, Britain, continental Europe, and Japan can be identified with considerable reliability on the basis of morphological examination. Samples of hybrid origin between North American and European plants tended to be similar to American cultivars, but often showed combinations of Old and New World characteristics, making their identification problematical.
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Ernest Small (1981) studied this question.
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