Alien ≠ Invasive

As the weather warms and wildflowers and weeds start emerging, and gardeners and botanerds start talking about the coming growing season, words get tossed around and, sometimes, misused.

Not long after I finished writing the post about the word native, the very topic of “alien invasives” came up in a forum I moderate. The topic was dandelions. Are they alien invasives?

It’s important to understand that although those two words are often used together, “alien” and “invasive” are two different concepts. “Alien”, like “native”, refers to origin, while “invasive” refers to growth habit.

Yes, dandelions are alien in North America. But they are not necessarily invasive.  Here are some legal definitions:

‘‘Alien species’’ means, with respect to a particular ecosystem, any species… that is not native to that ecosystem….‘‘Invasive species’’ means an alien species whose introduction does or is likely to cause economic or environmental harm or harm to human health

National Environmental Policy Act, 42 USC § 4321

Note that by definition, invasive species are aliens, but it is not necessarily true that alien species are invasive.

Vinca minor (periwinkle), alien and invasive; please don’t plant it

So we often ask ourselves: is it ever okay to grow aliens? I believe the answer is yes, so long as they aren’t invasive aliens. Remember: first, do no harm. If you’re considering planting an alien or naturalized species, or even a species that’s native to some place nearby, do a little research. I would have no qualms about planting Baptisia australis, but I’ve removed Stylophorum diphyllum from my garden, because I see it spreading pretty aggressively in nearby woods. (See Nativity and Granularity)

Also, consider this statement from

…it is nearly impossible to predict which species will become invasive and new species are being introduced every day. Some species are present for many years before they exhibit invasive characteristics. Many invasive species go through a “lag phase” in which their populations grow slowly until they reach a size large enough for the population to explode and/or become adapted to the local environment and become invasive.

The responsible gardener keeps her eyes and ears open, and promptly removes anything that’s been re-classified as invasive (as I did a few years ago with Nandina domestica).

Galanthus nivalis (snowdrops); obviously naturalized but not yet dubbed invasive

This issue of invasive aliens gets complicated. Since I am definitely not an expert, I’ve complied a list for further reading. If you’re a gardener, pay special attention to your local and state laws regarding problem species, like Maryland’s new regulations about the sale of invasive plants.



Invasive Species 101  -Center for Invasive Species and Ecosystem Health
Mistaken Identity – Invasive Plants and Their Native Look-Alikes, Delaware Department of Agriculture
What Are Invasive Plants? -Virginia Department of Conservation and Recreation
The Problem with Invasive Plants -City of Portland, Oregon Environmental Services
Invasive Species: What You Can Do -The Nature Conservancy
Frequently Asked Question About Invasive Species -US Fish and Wildlife Service
Compilation of Regional Invasive Plant Species Lists  -University of Maryland Cooperative Extension

-with thanks to Kerry for pointing me at several publications

Sometimes, It’s About Perspective


Queen Anne’s Lace
aka wild carrot, bishop’s lace
Daucus carota



This is probably the plant from which modern carrots were derived, and so we owe it some respect.  Except that it has escaped cultivation and grows wild all over the US and most of Canada and is a serious pasture pest.  Four states list it as a noxious weed.


When I was a child “summer” meant riding in the back of my parents’ convertible, watching the Queen Anne’s lace and chicory* go by on the roadside. So pretty!  That might even be my earliest memory of “wildflowers”, though the grown-up me dismisses them as alien invasives.


At any rate, I haven’t paid attention to Queen Anne’s lace in years.  Never even took a photograph of one until recently.  While hiking along the C&O Canal towpath near lock 8, I saw some particularly tall specimens with flowers just starting to open.



I was quite taken with the form, and spent some time shooting them from different angles.






It’s really striking this way, isn’t it?  Much more aesthetically pleasing, and harder to dismiss as a roadside weed.20150716-20150716-_DSC0008


*chicory, aka cornflower and a host of other common names; Cichorium intybus, Asteraceae: