Key for the main assortment of Ilex aquifolium cultivars in Central Europe based on leaf morphology.

In nursery practice and especially in plant trade, the authenticity of cultivars of Ilex aquifolium is a widespread problem. Unavailable cultivars were substituted with similar cultivars without declaration. Existing keys are based on only a small number of cultivars or comprise too many rare cultivars. The aim of this work is to establish a key that is easy to use for common cultivars in Central Europe, based on parameters that are easy to identify. In this investigation it was found that the high variance of leaves among the cultivars is ideal for this purpose, and is therefore proposed as parameter. In the first step the main assortment in Middle Europe was identified. From these cultivars, morphological parameters of sun and shade leaves were surveyed to describe the within-taxon variance. Taxa inside and outside the natural distribution area of Ilex aquifolium were investigated to account for climatic influence. The following parameters were examined: pedicel length and colour; leaf form, length and broadness, leaf edge corrugating; leaf vein number; prickle number and length. Results showed a variance between the cultivars high enough, and an inner-specific variance low enough, to construct the key. The leaf parameters were complemented with parameters of other plant organs for greater precision. The key comprises 16 cultivars of Ilex aquifolium taken from the enlarged standard assortment available in good garden markets and better nurseries. It was enhanced with rare local cultivars that show great similarity to cultivars from the standard assortment.