8 minute read
Do Cultivars Support Biodiversity?
By: Keith Nevison, Director of Horticulture and Operations
Congratulations! Your interest in native plants has piqued and you are inspired to start a garden from scratch this spring. You diligently research native plants from a trusted resource (perhaps Calscape.org or “California Native Plants for the Garden”), selecting for flower color, mature size, drought tolerance, and amount of sun required per day. You feel ready to visit a local nursery and start purchasing from your list. But wait a minute. You arrive to find a jumble of names associated with the plants you’ve planned: ‘De La Mina’ verbena, ‘Bee’s Bliss’ sage, ‘Howard McMinn’ manzanita, ‘Concha’ ceanothus, ‘Wayne Roderick’ seaside daisy. How does one decipher this plant code, and what does it all mean? Fret not — you've stumbled across the world of cultivar names, and I’m here to help you navigate it.
What Is a Cultivar?
Before we begin discussing how cultivars factor into a biodiverse garden, we should define cultivars and discuss how they relate to the world of plants. At its basic definition, a cultivar is a botanical contraction of a few words: “cultigen” or “cultivated” and “variety." This neologism, aka new word, was coined in 1923 by the famed Cornell University horticulturist Liberty Hyde Bailey to distinguish between wild plants and those selected, grown, and adapted through human cultivation. The process of selecting plants to become distinct cultivars typically begins in a wholesale nursery by plant breeders or growers who notice a unique plant characteristic that is different than a wild species that it’s closely associated with. A desire to preserve those features is what drives new plant selections and the development of cultivars in the nursery trade, which each year sees more options arrive at your retail nursery. With different nurseries promoting their own cultivars, it’s not unusual to see cultivars rivaling or outnumbering their straight species counterparts when shopping for plants at the nursery.
From Hybridization to Cross-pollination
Okay, we’ve defined cultivar, but how do plants emerge with desirable features that warrant selection in the first place? The process of creating a new plant cultivar can come about in a variety of ways.
Some cultivars are the result of careful breeding and hybridization efforts done over years by a plant breeder curious about combining the qualities of two closely associated plants through the process of controlled cross-pollination. Good examples of this are the myriad options of Pacific Coast irises (Iris spp.) or coral bells (Heuchera spp.) that are found in many locations throughout Santa Barbara Botanic Garden.
Sometimes natural hybrids result via a spontaneous cross that happens when two nearby plants connect without human interference. One good example of this is ‘Roger’s Red’ grape, which was determined to be a wild California grape (Vitis californica) crossed with a European common grape/wine grape (Vitis vinifera) that was found growing near the Russian River by noted Bay Area horticulturist Roger Raiche.
Yet another method for selecting cultivars happens when a wild plant is identified in a natural population that is unique from others that are adjacent to it. This is the case for ‘Avis Keedy’ hummingbird sage, a yellow-flowering version of hummingbird sage, which is beloved for its tropical fruit punch aroma and ability to thrive in shady settings.
How To Identify a Cultivar at Your Nursery
What distinguishes cultivars from wild species is the application of a cultivar name, identified in a plant’s name inserted in single quotes. This is how we get plants named for significant botanists — ‘Lester Rowntree’ manzanita, for instance — as well as names that evoke images from some of the iconic locations of our state, such as ‘Pigeon Point’ coyote bush. By the way, another in vogue term that you might come across in the horticulture field is a “nativar,” which is shorthand for a native cultivar. The more you know!
Do Cultivars Support Biodiversity?
Now that we’re well into our tour of cultivars/nativars, let’s discuss what role they have in a biodiverse garden. Most cultivars are unlike wild species in that they typically require reproduction via cuttings in a greenhouse in order to keep the desirable trait inherent in the plant. Wild species on the other hand are often grown from seed, which ensures that different plants have genetic distinction from each other. The question arises, “Is it disadvantageous to wildlife to plant a garden primarily featuring cultivars as opposed to wild species?” The answer to this question informs modern research on this topic, which has heretofore been conducted in experiments on native plants and cultivars, principally in the New England and mid-Atlantic regions in the U.S. In fact, my own graduate research on this topic involved an experiment surveying pollinator attraction in the Genus Phlox, comparing several species with their cultivars to determine if notable differences were present. Samples of nectar were taken to analyze whether cultivars differed from wild, straight species in sugar content, which could help explain levels of attraction as well. Long story short, at least for Phlox, deliberately bred cultivars featuring larger flowers or abnormal colors were not as attractive as straight species, but the most attractive plant in the study was a cultivar derived from a wild population which has smaller flowers produced in copious quantities, giving more opportunities for moths to drink nectar, thereby supporting a larger number of pollinators than the wild-type garden phlox (Phlox paniculata). This is a topic that remains relatively unstudied in the Western U.S., and our Garden team is very keen to set up horticultural experiments in the future to shine more light on this question.
At the end of the day, the safest method of ensuring high-quality habitat in your garden is to strive to establish native plant species that occur naturally or occurred historically in your area. Ultimately, native plants have evolved over millions of years in concert with native wildlife, so we can rest assured that these wild plants will feed and shelter our native mammals, birds, reptiles, amphibians, invertebrates, and other creatures occurring around our homes.
With that said, back to our original predicament, it can be difficult to find wild species at the nursery with cultivars in ever-increasing dominance in the marketplace. There are a few different approaches therefore to consider. One is to grow your own native plants from seed to ensure that you are contributing to natural biodiversity, providing the genetic diversity that will keep the creatures in your garden healthy and thriving. Another is to experiment with using some native cultivars. Here at the Garden, the sections of our Living Collection feature a wide ranging mix of cultivars and wild species, which we have ethically harvested from across the California Floristic Province since our founding in 1926. In fact, our long history in the realm of California’s native plants features more than 35 years of work (1955–1992) with renowned horticulturist and plant breeder Dara E. Emery. He created many important cultivars, through the Garden’s Plant Introduction Program, that remain popular today.
Since we grow such a wide array of wild species along with cultivars in our collection, we take comfort in knowing that we have abundant habitat available for our beloved songbirds, chorus frogs, butterflies, and even occasional night-roaming bobcats and mountain lions that wander through the margins of our property.
Especially for those starting with a predominantly nonnative landscape, cultivars can be a positive step in the direction toward growing 30% native plants in our urban landscapes (https://resources. ca.gov/Initiatives/Protecting-Biodiversity), one of the Garden’s defined strategic goals to ensure biodiversity thrives. Cultivars can be a gateway into the larger, diverse world of native plants, so feel free to consider finding a place for them in your native landscape, working them in between straight species for maximum positive environmental impact.
