The genus Juniperus is the third largest in the coniferales, and its many species are not only widespread but also extensively cultivated. Several factors make the classifying of horticultural junipers both difficult and confusing. First, the species are ill-defined since there are few good key characters and few qualitative characters. The numerous quantitative characters vary considerably. The characteristics of the reproductive organs, fruit characters, vary as much as those of the vegetative body. Secondly, natural hybridization at the species level is widespread and the recombinations are occasionally bizarre. Thirdly, horticultural selection is made by man without concomitant analysis of the variability of the populations at the site. Thus, it is often difficult to determine just which species a variety should be referred to. Fourthly, many of the selections are based on odd growth habit or aspect, low growing, cup-shaped, vase-shaped, upright, etc., and growth form is controlled in some cases by single gene differences, in others by polygenes.