6 NATL. ARBORETUM CONTRIB. NO. 3, U.S. DEPT. AGR. 



Dates of cultivation for introduction are important in establishing 

 priority of a name and publication and have a determining and critical 

 influence with the history and nomenclature of cultivated plants, as well as 

 with validation of cultivar names. The terms "cultivated" and "intro- 

 duced' ' are considered synonymous; however, divergent information is 

 available from numerous authors; for example, Bean, Boom, Elwes and 

 Henry, Krussmann, and Rehder. 



Dates for the publication of valid cultivar names are accepted when 

 there is evidence with respect to at least one of the following points : 



• Asexual propagation. 



• Cultivation in any botanic garden, arboretum, nursery,, or garden. Often 

 the cultivation of plants in botanic gardens and arboreta alone is not 

 accepted by some as having been introduced to the public. But these names 

 are accepted by this checklist as bona fide cultivated plants when validly 

 documented. Published and publicly distributed lists from botanic gardens 

 and aboreta have been a particularly fertile source of cultivar names 

 Although these institutions rarely sell plants to the public, their material 

 ultimately becomes available to the public. Botanic gardens and arboreta 

 are important sources of plant material, particularly of new selections, 

 for the nursery trade. 



• Dissemination of sexual and asexual propagations, although concrete 

 evidence of successful cultivation may be lacking. Possibly, all species or 

 clonal selections reported as introduced are not currently under cultivation. 

 There are instances of plants that occur in the wild and may not have been 

 disseminated or propagated. When there is obvious evidence that these 

 plants have been given intensive care at their natural site, they are ac- 

 cepted as being cultivated. 



Group Names 



Group names in themselves are not new to cultivated Ilex; J. C. Loudon, 

 in his "Arboretum et Fruticetum Britannicum ,, in 1838, described several 

 groups referring to Ilex aquifolium. 



In this checklist of /. opaca, group names, not cultivar classes, are de- 

 fined as assemblages of cultivars that have one or more natural or unnatural 

 relationships in common. For example, the components of the (Grace 

 Hybrid Group) are naturally related because they are all progeny from the 

 same intraspecific cross. On the other hand, members of the (Aalto Group) 

 are related because all are clones selected by Wilfred Wheeler from a wild 

 population in a particular geographic location and subsequently introduced 

 into cultivation. 



In this checklist, no previously unknown group names are erected ; how- 

 ever, all group names that might be confused with cultivar names have 

 been enumerated. In this checklist, group names have no taxonomic rank 



