A cultivar is a variation on a plant that has been selected by human intervention to be different (ie, “improved”). The straight species is one that has evolved and reproduces in the wild.   

A good example is the coneflower. The straight species is a simple, daisy-like purple/pink flower with a brownish orange center. The species name is Echinacea purpurea. If you go to a conventional nursery or look in a catalog, you will see all kinds of variations of Echinacea in many colors, and sometimes with double flowers. Echinacea ‘Cheyenne Spirit’ is a cultivar that comes in shades including orange and yellow. The name in single quotes is the tip-off that it’s not the straight species. (It can also be named Echinacea x ‘Cheyenne Spirit’ or Echinacea purpurea ‘Cheyenne Spirit’.)  

In most cases, a cultivar is not as ecologically useful as the straight species.  The nectar and pollen may be absent, reduced, or unavailable to the insects that need it. The novel color changes that are so attractive to human beings may render the flower unrecognizable to pollinators. If the foliage has been altered to be a different color, the caterpillars and other insects that need to eat it may not be able to digest it. At this time, it appears that changes to the plant’s growth habit, such as height, still allows it to be useful as a host plant.

Another problem with cultivars is that many of them are grown from cuttings of a single original plant. They are all clones and genetically identical. Preserving genetic diversity in a species is essential for its ability to adapt to short and long-term changes in the environment, such as floods, heat waves, drought, invasive pests, and climate change. Seed grown plants, which are pollinated by insects, maintain the genetic diversity that provides species resilience, and allows plants to evolve and adapt to changing conditions. This is important to overall biodiversity.

Following the work of Doug Tallamy and Desiree Narango, we recommend that you plant straight species, not cultivars, for at least 70% of the plant biomass in your landscape.