What Is A Native Plant?

“Native” has become a buzzword in the world of botany and horticulture, and I guess I’m contributing to it! Suddenly a bunch of people who didn’t care where their plants came from are ready to lionize one group of plants and villainize another.

But what does “native” actually mean?

This is a question that Mark Richardson and Dan Jaffe attempt to answer at the beginning of Native Plants for New England Gardens:

Generally speaking, native is defined by “where” and “when.” In other words, native plants are considered to be those that existed in a given location at a specific point in time.

Sharing an Evolutionary History

First, let’s talk about the “when,” because it’s not quite the minefield that the where is.

According to Richardson and Jaffe, “for simplicity’s sake… if the plant was in an area at the time the first European settlers arrived, it is considered native.”

(I assume “we” here can be understood to mean Native Plant Trust, as both Richardson and Jaffe are affiliated with it. They are a reputable source, and are where I am pursuing my Native Plant Studies certificate!)

This view is, of course, hella Eurocentric and imperialist, and the fallibility of human records makes it even more questionable.

Luckily, we don’t have to rely on that. The key piece here goes back waaaay beyond the 300-400ish years since European settlement. We’re talking about the evolutionary history of the plant and its surrounding ecosystem.

If two species share a long evolutionary history in a given ecosystem, they come to depend on each other. In particular with plants, that plant becomes a source of food for animals that co-evolved with it – bees, ants, Lepidoptera, birds… right on up to “charismatic megafauna” like deer, bears, and humans. In other words, it becomes a keystone of the food web.

In Douglas Tallamy’s book Nature’s Best Hope, he uses the example of Phragmites australis (the common reed) to illustrate this:

The common reed, Phragmites australis, provides a great example. The European genotype that has displaced wetland vegetation from the Atlantic coast to the shores of Lake Michigan has inhabited North America for hundreds of years. There is good evidence that it was used as packing material in the holds of the earliest sailing ships some 500 years ago. In Europe, phragmites supports 170 species of insects. After hundreds of years of residence in North America, only 5 insect species are using phragmites as a nutritional resource (Tewksbury et al. 2002). Adaptation is happening, but at a glacial rate typical of evolutionary change.

Basically, the “when” of “native” here hinges not just on recorded history, but on the entire evolutionary history of that plant, as evidenced by other species’ dependence on it.

So now let’s get into the hairier question of “where.”

Nature Doesn’t Recognize Borders

One of the best sources for answering the question of “is this plant species native to North America/my state/my county?” is BONAP, the Biota of North America Project.

But here’s the thing. Plants don’t obey the arbitrary lines humans draw on the ground. “Life,” in the immortal words of Jurassic Park, “finds a way.” That could be next door, next county, or across an international border.

Look at a plant like Hypericum kalmianum, Kalm’s St. John’s Wort. You’ll see that it’s native to New York state (the dark green color), but is not found in Massachusetts (the tan color). Furthermore, the bright green of Rensselaer County, New York’s capital district, means that it’s native, present, and not rare in that county.

But these two states border each other, and Rensselaer County is right next door to the western border of MA. If you find Kalm’s St. John’s Wort in, say, Stephentown, NY, in Rensselaer County, no question, it’s native.

But if you find it 2.8mi away in Hancock, Berkshire County, MA, is it not native?

According to the U.S. Forest Service, the seeds of (a different) Hypericum are dispersed by “wind, water, humans, and other animals.” Ruling out human means, that still leaves a lot of “natural” possibilities for movement. What if a grouse ate some of the seeds in Stephentown and flew off to poop them out in Hancock? What if a stream carried the seeds from one town to another? What if a bad storm blew the seeds that distance?

2.8mi is not a very long distance for a seed to be dispersed.

It’s completely reasonable to assume the parent plant shares an evolutionary history with many of the species found in both places. This article “Native Shrubs for Small Yards” tells me H. kalmianum provides pollen for “leaf-cutting, Halictid and bumble bees”, and I guarantee there are all of those in Berkshire County, MA.

This is a bit of facile example. H. kalmianum is what native plant enthusiasts often call a “near-native” in Massachusetts. I doubt even the strongest native plant evangelists would have a problem with planting it in MA.

Let’s tackle a thornier example: the much-maligned Robinia pseudoacacia (black locust).

haaaaa “thornier” because it has thorns, get it? I crack myself up.

Specifically, let’s talk about it in the context of New York state, where it’s a weird corner case.

It’s on the New York DEC’s prohibited (i.e. invasive) plant list. Seems pretty cut and dry, right?

But look at the species on BONAP. According to this, it is native to certain counties of New York, including Franklin County (that county in dark green in the far north). But it’s adventive (non-native) in the majority of counties in New York state (the teal color), including neighboring Clinton County.

As it happens, I grew up in Clinton County! I’ve observed black locust in both of those counties, with no distinction between them. As with the earlier example, there are also towns that straddle the county border with single-digit distances between them.

Plus, that area is in the foothills of the Adirondacks, and approximately a gazillion small streams drain from the mountains into the Chazy and Saranac and Ausable Rivers. Those waterways travel through Clinton and Essex Counties, and end up in Lake Champlain – which connects to the Hudson River, the St. Lawrence Seaway, and ultimately the Atlantic Ocean!

What am I to make of this, then? How can a plant be native in one county but invasive 5 miles, or 5 feet, away? Is the food web and evolutionary history so different between the two counties?

It’s easy to say that, say, Reynoutria japonica (Japanese knotweed) is a non-native invasive in the US. Japan is an ocean away, and it wouldn’t even be on this continent (or in Europe) if a British botanist didn’t send two samples from Japan back to the UK in the 1880s.

But it’s not always so clear cut a case. Sometimes, as I’ve shown, “the call is coming from inside the house.”

(Richardson and Jaffe suggest the concept of ecoregions as an alternative to land borders, and that has merit, but at the end of the day the boundaries are still subject to some degree of human judgment).

What I conclude here is that – at least within a continent – “native” still has some room for interpretation.

Climate change weirds everything

To add an additional hiccup here, climate change is causing all species to expand their range (further north, usually). You may have noticed that recently the USDA zone hardiness map changed; I’m now in the warmer zone 6a, whereas I was in 5b before.

(NB: These zone map changes are not necessarily due to climate change. Some of the shifts could be explained by improved data over the previous ten year period. But it’s a convenient example).

While climate change is obviously anthropogenic (caused by humans), it’s not exactly “some dude brought an invasive plant over from Japan because he thought it was pretty.” It’s more like “some animal pooped out the seeds here and (thanks to climate change) it seems to thrive.” It’s a degree removed, and it feels different somehow. I think botanists and native plant enthusiasts are still trying to figure out what to do with this information.

Cultivars/nativars

Human cultivation has also acted on native species. There’s a concept of “nativars” – native species that have been human-cultivated to have a particular aesthetic characteristic. The ‘Husker Red’ cultivar of Penstemon digitalis (foxglove beardtongue), selected for its striking red leaves, is a good example of one. (I happen to have it in my garden!)

Do nativars count as natives? Do they fill the same role in the ecosystem that the straight species does? That’s going to vary based on the dependent species and the nature of the cultivar. Does a different leaf color make it less likely for butterflies and moths to lay their eggs there? Does the cultivar have less nutritive pollen or nectar?

And then there’s the genetic diversity question. These plants are usually hybrids, which have to be propagated vegetatively to maintain their cultivated traits. Propagation vegetatively, by cuttings or similar, produces genetic clones of the original plant; it’s not benefiting from the gene recombination that happens when plants reproduce sexually.

This is not great. For an example of what happens to a group of organisms when its loses genetic diversity, I present as evidence the entire Habsburg dynasty of Europe.

These are all things to consider – and a matter of hot contention in the native plant community!

(It’s worth noting Native Plant Trust sells selected nativars; I got an Oenothera fruticosa ‘Fireworks’ at their fall closeout sale).

So what does this mean for Red Trillium Gardens?

For the purposes of what plants we grow, native means “native to at least one state of New England or New York (and not on any prohibited plant lists).”

(I include New York because I’m originally from upstate NY, and I feel like it shares a lot of cultural and ecological identity with the rest of New England. Unless you’re talking about baseball, of course!)

So yes, we grow Kalm’s St. John’s Wort. We also grow Rudbeckia fulgida, orange coneflower, which is only native to Connecticut in New England. But we certainly aren’t going to be growing Robinia pseudoacacia!

I’m not going to be policing anyone’s usage of these plants, either – just providing the information to make an informed choice.

tl;dr

I’ve gotten long-winded, so let me sum up with a quote from Richardson and Jaffe: “native plant” means “the right plant for the right place.”

But as we all know… “right” is subjective.

So instead let’s borrow a term used in the psychedelic drug community: “set and setting.”

In this model, both your mindset AND the external environment are important in defining a native plant.

By “mindset,” I don’t mean that if you think hard enough, you’ll make Japanese knotweed native! But there’s ambiguity in the definition of “native,” and only you can decide where you draw the line.

Some folks are going to say “hey, it’s native to North America, that’s good enough for me,” and some aren’t going to plant any plant that BONAP says isn’t native to precisely their county.

Some will plant nativars; some won’t.

Some are okay with plants like Helianthus tuberosus (Jerusalem artichoke) – which was in New England when European settlers arrived, but only got here with assistance from Native Americans – but many aren’t.

Maybe this is why native plant communities can be so toxic, and tempers run hot. (Ask me why I left the Native Plants of the Northeast group on Facebook!) The stakes are high in this game – the extinction of native plants means the extinction of human life*. Maybe it’s no surprise, then, that people have strong opinions they hold onto for dear life.

*Yes, that’s an extraordinary claim, but Douglas Tallamy has extraordinary evidence. I highly recommend reading Nature’s Best Hope for more info. That was a significant part of my native plant “radicalization.” 🤣

Anyway! I’m not a native plant purist, but I do still feel strongly about their importance. (Obviously!) I just hope that after reading this, you know how to answer the question of “what is native?” for yourself.

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Featured image: Catalpa speciosa (Northern catalpa) photographed by Lise Fracalossi, Cochituate Brook Trail, Framingham, MA, June 2017. Catalpa is an example of a species that is only questionably native in New England (but that I adore). The Massachusetts Invasive Plant Advisory Group considered it for inclusion as an invasive in the state’s list, but ultimately decided it didn’t meet the criteria.

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