Monday, March 2nd, 2015
There is much discussion in the horticultural world regarding the use of cultivars of native plants versus using the species. This topic came up recently in reference to the new wildlife garden we are installing so we thought this was a great opportunity to discuss further.
What is a cultivar?
Often referred to as a combination of the words cultivated variety, the term was coined in 1923 by the great botanist Liberty Hyde Bailey to describe “a botanical variety that has originated under cultivation”. The origin under cultivation may be through selection, hybridization or genetic modification.
Selection is the most commonly used method when dealing with cultivars of native plants. Selection could be made from thousands of seedlings grown in a nursery or while walking through the woods and stumbling upon a branch sport. Plants may be selected for disease resistance, flower colour, variegated foliage, dwarf growth habit, or any number of variations on the original species. The vast majority of native plant cultivars are seedling selections.
Hybridization is the process of crossing one plant species with another and propagating their offspring. The following picture is a common landscape tree in the southeast, Ilex x attenuata ‘Fosteri’, aka Foster’s Holly. It is a man-made series of hybrids between Ilex cassine and Ilex opaca developed by Foster Nursery in Bressemer, Alabama. Hybrids will usually have an x following the genus name and may or may not be given a unique species name. Hybrids are usually man made but they can be cultivated from wild plants, oak trees for instance are notoriously promiscuous with other species sometimes making tree id difficult. Typically hybrids occur between species (interspecific) within the same genera, however crosses between genera (intergeneric) hybrids occasionally occur. An example is the crossing of the genus Heuchera (Coral Bells) with the genus Tiarella (foam flower) forming the new genus Heucherella or Foamy Bells.
Genetic Modification is rarely used in the development of native plants, mostly because of the cost. Typically engineered plants are developed for agriculture and are made for a particular purpose such as disease resistance or immunity to herbicides. Of course there are some exceptions, like genetic modification for blight resistance in the American Chestnut and new work being done on the fungal resistance of the American Elm, but in general genetic modification is used on agricultural crops.
So what are the issues with using cultivars? One of the most prominent issues is that native cultivars behave differently than the species causing problems with the local wildlife that relies on the plant. Using our native Echinacea purpurea as an example we can see some of the problems that cultivars possess. There have been dozens of new cultivars released over the past decade and some, like the photo at left, are double flowered making it nearly impossible for a pollinator to get into the nectar rich part of the flower. Also many of these new cultivars are sterile, meaning they do not produce viable seed, which is bad news for goldfinches and other native birds who love to eat the seed. Native trees and shrubs are often bred to have larger or differently coloured berries which may not be edible to wildlife populations.
Whether or not to use cultivars of native plants is a matter of personal preference, however if your goal is to aid wildlife and decrease environmental impact then it is probably better to go with seed grown species of native plants. This provides the greatest genetic diversity and will guarantee that the animals and insects we share this space with have what they need to survive.