Do 'nativars' count as native plants?

For the purpose of supporting biodiversity in general and native insects in particular, do we have to grow only the straight species or “wild-type” of plants that grew in our region before European settlement? What about improved versions of those plants, referred to as cultivars or “nativars”? This turns out to be a complicated question.

    Unless you’re shopping at a dedicated native plant nursery, you’re likely to find few unimproved natives at the garden center. Most plants offered as natives will be cultivars that have been selected by horticulturists for desirable traits such as bigger, brighter flowers or unusual foliage color. You can spot a cultivar by a name in single quotes: for example, Echinacea purpurea ‘Sundown’ is a purple coneflower cultivar.

'Sundown' was selected for its petals' orange tint-photo Mike Peel

    Sometimes a spontaneous mutation occurs in a plant population. An observant nursery may notice the plant’s changed appearance and decide it has market value. Other cultivars are purposely created through many generations of breeding or even through genetic modification. Some are hybrids between two species. 

     Are nativars useful in pollinator gardens? It depends. Selection for horticultural use may change flower size, color, time of bloom, or foliage color. Any of these could confuse insects seeking pollen and nectar or could mean that bloom doesn’t occur when the insects need it. 

Pollinators have evolved to synchronize their life cycle with bloom times of flowers they need

Double flowers are often sterile, because in the breeding process, pollen-carrying stamens have been replaced by extra petals. These won’t offer visiting insects any reward at all.

Echinacea 'Razzmatazz' won't help pollinators

    In general, it seems that the more closely a flower resembles the straight native’s, the more popular it will be with insects. It’s an area of active research. Doug Tallamy and Emily Baisden have found that woody plants with purple, blue or red leaves are not useful to leaf-eating insects, probably because of the anthocyanins that give leaves their pleasing colors.

Heuchera 'Amethyst Mist' is pretty, but not attractive to leaf-eaters

      Annie White intensively studied pollinator visits to test gardens of native perennials and cultivars of the same species at the University of Vermont. Delaware's Mt. Cuba Center ran another perennial trial. 

Doug Tallamy and Emily Baisden vacuum up insects for study at Mt. Cuba Center

     In general, the unimproved native flowers attracted more insects, but some cultivars were also winners. A culvers root (Veronicastrum virginicum ‘Lavendelturm’ and a garden phlox (Phlox paniculata ‘Jeana’) were visited by more insects than their straight native counterparts. Researchers speculate that this is because the culvers root bloomed for longer than the straight species and the phlox had shallower flowers that made nectar easier to reach. Hybridization made flowers less useful to insects when it radically changed flower color or reduced production of pollen and nectar.

Small, shallow flowers of Phlox 'Jeana' make nectar access easy

    For gardeners who’d like to participate, three universities are running a citizen science project called Budburst that invites us to plant some flowers from a list and contribute scheduled, structured observations of their insect visitors.

    What can we take from the preliminary research? Generally straight natives seem to do the most for insects, but many nativars are useful too. We can encourage our garden centers to stock the unimproved natives. And plant breeders can help out by selecting and marketing flowers that benefit pollinators.

Native flowers for pollinators

More complications in the search to provide habitat and food for pollinators emerged from a fascinating lecture I attended last week organized by Grow Native Massachusetts. Annie S. White spoke about her research comparing pollinator preferences for flowers of native perennials versus “native cultivars.” 

Annie counting pollinators in her test plot

Cultivars are plants that have been deliberately selected or bred for desirable characteristics, such as different flower forms or colors. 

    Annie’s research filled an important gap for gardeners who want to do the best thing for pollinators. When we shop at the garden center, we’re often choosing between cultivars of native plants. For example, purple coneflower, Echinacea purpurea, is so popular that breeders offer dozens of cultivars. 

Are my purple coneflowers the native species or a look-alike cultivar?

Instead of the plain daisy form with deep pink petals, you can have a range of colors and flower forms, going as far as showy (or ugly, depending on your taste) double flowers that don’t look much like the unimproved natives. 

Echinacea 'Summer Flower Pink'--highly modified from the native species

You may not be able to buy the straight species at all. Were we right in assuming that these cultivars were just as valuable to pollinators?

    Annie spent summers standing in her experimental plots counting the pollinators that visited the flowers. Her study of eleven New England native species and their cultivars found that the more the cultivars differed from the native species, the less they offered to pollinators. In the case of purple coneflower, pollinators liked the native flowers best, accepted a white-flowered cultivar with little difficulty, 

A white coneflower cultivar is good enough for this bee

but eschewed a double-flowered variety and a sterile hybrid. 

    Double flowers are often sterile, because stamens have morphed into extra petals. So the pollinators get no pollen from these flowers. No wonder they’re not attracted to them. 

    Annie did a lot of detective work to uncover the origin of the native cultivars she studied. I was surprised that several turned out to be hybrids, or crosses between two species, although they were not labeled as such. 

     To make things more complicated, even seeds may not be accurately labeled. A study of sundial lupine seeds (Lupinus perennis)  recently found that only two out of ten sources were providing the true native species. The rest were seeds of naturally-occurring hybrids between the natives and cultivars that either escaped from cultivation or were intentionally planted along highways. 

Wild Maine lupines have interbred with cultivars

     Interestingly, the majority of Annie’s plants were pollinated by bees, with bumblebees leading the way, honeybees next, and a mix of native bees third. Only two percent were pollinated by butterflies and moths.
 
     For us amateurs, what’s a reasonable procedure for choosing plants that benefit pollinators? First we have to make sure the plants we buy haven’t been treated with systemic insecticides such as neonicotinoids that kill bees and other pollinators. Then we have to do our best to find native species or cultivars that have been only slightly modified. 

This black-eyed Susan cultivar must be close enough to the native species to attract pollinators

Easier said than done. I hope Annie’s research heralds a new awareness among growers so that in future we’ll be offered plants that are truly pollinator-friendly.