Greges, Clones and Cultivars
Herb Spady, Portland, Oregon
Reprinted from Portland Chapter Newsletter
Much confusion exists in the naming of rhododendron cultivars. Early rhododendron hybridizers either had little appreciation of the genetic diversity existing in the species or little appreciation of genetics. Crosses between species were given a grex (Latin for flock, herd or troop) name. One might assume that the practice arose because primary crosses between two clones of different species show a lot of homogeneity in the plants raised from the same seed pod. Even among those clones there will be differences. Consider a specific example such as 'PJM'. Take some distinctively different clones from the same species to create a hybrid and the result will be very different. Would the cross R. carolinianum var. album x R. dauricum var. album look anything like 'PJM? The original cross of R. thomsonii x R. griffithianum was made by Smith and named 'Cornish Cross'. Under such a system all seeds from the same seed pod and all crosses of all the different plants of R. thomsonii x R. griffithianum would have the same name regardless of obvious differences! Under such circumstances, going to a nursery to buy 'Cornish Cross', one would have no idea what they were buying except in a general sense. When this system of naming was first discouraged, knowledgeable rhododendron hybridizers identified specific clones with distinctive names even though similar, e.g., 'Exbury Cornish Cross'. That might be acceptable to the careful gardener and nurseryman, but might well be shortened by those not so careful. Look in the list of hybrids in David Leach's book and you will find each name identified by a "g," or "cl." This indicates that the name is a grex or a clone name. Be careful and try to identify specifically those plants that you buy that have a grex name.
It is unfortunate that there is even some sloppiness in the naming of modern hybrids. We hear remarks like, "This is a better form of 'PJM'," or "There are several forms of 'Virginia Richards' in the trade." All rhododendron cultivars should be identified as such, and when registered and in the trade by a specific name. These are plants that are unique and have been propagated vegetatively. They do not show variations from their plant of origin. They are really the same plant with a different root system. In the living world this is the closest thing to immortality!
Cultivar is a term used for plants that have originated in cultivation as contrasted to growing naturally in the wild, or from wild collected seed. This applies to man-made crosses, intraspecific or between species. A botanist might not consider an intraspecific cultivar to be a true species plant because such an artificial cross may have no opportunity to occur in the wild although both parents are considered to be the same species.