While this may seem like dry, “into the weeds” information to some, we find it important to understand the role plant genetics and cultivars play in horticulture. Below is an excerpt of a Plug article sent out this Fall from North Creek Nurseries.
Understanding the Terms
Cultivar: An assemblage of plants that have been selected for a particular attribute or combination of attributes, and that is clearly distinct uniform, and stable in its characteristics and—when propagated by appropriate means—retains those distinct characteristics. These characteristics are distinct and different from wild populations of that plant.
Hybrid: In biology, a hybrid has two meanings. The first being the result of interbreeding between two animals or plants of different groups. Hybrids between different species within the same genus are sometimes known as interspecific hybrids or crosses, i.e. many of the new Echinacea releases. Hybrids between different sub-species within a species are known as intra-specific hybrids i.e. Rudbeckia fulgidaintroductions. Hybrids between different genera are sometimes known as intergeneric hybrid i.e. the new "Echibeckia" releases where they cross Rudbeckia and Echinacea. The second meaning of "hybrid" is crosses between populations, breeds, or cultivars of a single species. The second meaning is often used in plant and animal breeding.
"True to Seed" Plants: Plants are often chosen for one or a combination of the following factors: function, aesthetics, site adaptability, or management. The selected plant and its distinct characteristics are able to be passed by seed (sexual propagation) when the selected plants are isolated from other plant populations. Offspring from the selected plant is the same in aesthetic and function as their parent plant material.
True to SEED native plant CULTIVARS
Plants that are propagated are not as simple as all plants produced by seed are good because they have genetic diversity and all the plants produced by cuttings are bad because they have all the same genes. Seed cultivars and where they stand in the spectrum of plant genetic diversity, of seed to asexual propagation, are not black and white—they’re in a grey area.
How is a SEED CULTIVAR produced, and does it still maintain genetic diversity?
Some plant species are not as diverse as others. There are species of plants capable of self-pollination or pollination within a limited population that results in genetically homozygous, “true-breeding from seed”lines. Without human manipulation, certain plant traits will continue to come true from seed as those traits are dominant in a specific population. ‘Seed Cultivars’ are plants grown from seeds collected from these limited populations.
Native jewelweed is a common example of a limited population. Orange flowers are jewelweed’s common, dominant color. However, on occasion, jewelweed can be found to have yellow flowers. These yellow flowers are not a dominant trait in the overall jewelweed population, but if yellow-flowered jewelweed is growing only near other yellow-flowered jewelweeds, its seeds will continue to produce yellow-flowered plants. The genetics required to produce orange flowers are not present in the population, and the recessive yellow-flowered genetics will be expressed.
NOT ALL CULTIVARS ARE HYBRIDS
Cultivars aren’t just about cross-pollinating two very different plants to create attractive offspring. Cultivated varieties ('cultivars') of plants can come from many sources.
There are cultivars that come from open-pollinated seed where someone has found a unique, desirable characteristic in an isolated plant population. Seeds from this population result in offspring which retain the unique characteristics of their wild parents. These cultivars, named ‘seed cultivars’ or 'true to seed cultivars', are introduced to the nursery trade when the plant species has no subspecies, varieties, or forms listed by botanists for that particular trait. The cultivar name, a horticultural designation, distinguishes plants with the unique trait from more typical examples of the species.
Cultivars are plants selected for distinct characteristics that differ from typical wild characteristics and keep these distinct characteristics when propagated. But, that doesn’t mean that these cultivars must be asexually propagated. They can be propagated either sexually or via seed and still maintain the distinct characteristics that allow for the plants to be given a cultivar name. An example of this? Salvia lyrata ‘Purple Knockout’.
What made the selection S. 'Purple Knockout' different from its species was its red foliage. There is not a taxonomic designation for the purple leaf form of this plant because it happens so irregularly in nature. However, through isolation, horticulturists have stabilized the purple leaf form as a horticultural plant and can sow it as a “true to seed” cultivar. It has, essentially, become a true breeding line of homozygous, identical traits for the red leaf form of our beloved native, Salvia lyrata.
The rest of Salvia lyrata genetics are still in there - there's just been selection for genetics that express that red leaf form. Do green leaves still show up when we sow dozens of flats? Certainly. Part of propagating these plants for our industry involves removing green-leaved seedlings and collecting seeds from red-leaved plants to sow to ensure greater reliability for the desired trait of red leaf color.
What does all of this mean for you, the person working with the plants in the landscape?
A plant is not "bad" or "good"—that language is designated and labeled by each individual who views the plant, just as a hammer isn't "bad" or "good" but merely an object attempting to fulfill a purpose. A hammer only becomes "bad" when it is the wrong tool for the job. Where a plant is planted, how it performs in that environment, or whether it’s congruent with an individual’s belief system, is what shuffles a plant into the subjective category of “good” or “bad”.
If the goal is to conserve or restore a natural area, native endemic plants that contain wider genetic possibilities and will help restore genetic diversity in the population may be the better tool for the job.
If the goal is to create an aesthetically-pleasing garden with specific ornamental characteristics, plants selected for flower color, height, and habit may be more desirable and appropriate considerations.
Seed cultivars can be as morally muddy as people want them to be (or not be). It's up to the individual to determine which plants best fulfill your intended purpose.