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

Never Assume

Every year I see this garden escapee along the Billy Goat C trail, and every year I think “yep – Muscari armeniacum“, because I know that plant from many years of gardening.

But, I’m always fact-checking (or second-guessing) myself, so I looked up M. armeniacum, just to be sure. Imagine my surprise when multiple authorities show it present in North America, but nowhere near the Mid-Atlantic.


The same authorities show two other Muscari species, M. botryoides and M. neglectum, in the Maryland piedmont, so I checked Weakley’s Flora, and believe this to be M. neglectum. Unless it’s one of the cultivars. I think for the purposes of this blog, it’s good enough to say it’s a Muscari.

There are numerous Muscari species and cultivars in the nursery trade, all of which go by variants of the common name grape hyacinth. Previously placed in the Liliaceae, they’re now listed in the Asparagaceae. They’re easily grown bulb-forming perennials that bloom early and spread nicely in the garden, which is why they’re a problem: they naturalize a little too well.

Populations of the various Muscari are now established in much of the US, excluding the Great Plains and the mountainous and desert regions of the West. I haven’t found any official listing of it as invasive other than in Tennessee, but that may be a matter of time.

The long, grass-like leaves in these pictures belong to the grape hyacinth; it’s growing in a patch of golden ragwort, which has the heart-shaped leaves.

Early Spring Aliens

At the end of February, technically still wintertime, I saw this carpet of white on the Cabin John Trail. It wasn’t spring beauties, and it wasn’t leftover snow, either.

This is Galanthus nivalis (snowdrops; Amaryllidaceae), a perennial native to Europe. It naturalizes well, meaning you can plant a few dozen bulbs and enjoy the show year after year as they spread through your garden. Unfortunately, it naturalizes a little too well, and so can be found in woodlands throughout the mid-Atlantic, as well as some other parts of the country.  The National Park Service doesn’t list the species in its manual Plant Invaders of Mid-Atlantic Natural Areas, but the University of Maryland Cooperative Extension considers it invasive.

What exactly does it mean to be “invasive”? I like the USDA Forest Service definition:

An “invasive species” is defined as a species that is

  1. Non-native (or alien) to the ecosystem under consideration; and,
    2. Whose introduction causes or is likely to cause economic or environmental harm or harm to human health.

Whether or not snowdrops cause environmental harm may be just a matter of degree, or time.

I didn’t know that snowdrops were a problem before researching them for this post. Now there’s another item on my garden to-do list: pull out the snowdrops.

When it comes to Vinca minor (periwinkle; Apocynaceae), though, there’s no doubt. At least twenty-two authorities consider it invasive. It’s easy to find at this time of year. If you follow some of the footpaths near Carderock to the base of the climbing wall, you’ll find vast slopes of the stuff, competing with the Dutchman’s breeches, squirrel corn, Virginia bluebells, and trout lilies that belong there. The plant roots easily at the stem nodes, and since the long stems trail along the ground, it spreads quickly. This characteristic, along with evergreen leaves, pretty purple flowers, and tolerance for a variety of growing conditions, makes it a popular groundcover in home gardens. Please don’t plant it.

next time: more aliens


Our Earliest Spring Wildflowers


How many different species are shown blooming in this very small area?

Two days ago the Maryland Biodiversity Project held a single species bio-blitz: submit photos of purple deadnettle (Lamium purpureum) blooming that day. With about an hour to kill before heading out for another activity, I got the camera and went for a walk in a nearby park.

Before finding a few of the target plants, I snapped quick photos of anything else that was flowering. I found hairy bittercress (Cardamine hirsuta), two or three types of speedwell (Veronica species), dandelion, (Taraxacum species), and henbit (Lamium amplexicaule) in open areas, and in the woods snowdrops (Galanthus nivalis) and periwinkle (Vinca minor).

These wildflowers have something in common, other than being our earliest blooming plants: they’re all aliens. The only natives blooming now are skunk cabbage (Symplocarpus foetidus) and some maples (Acer species). And some stupidly early spring beauties, as I reported last week.

This got me thinking. I have pictures of literally hundreds of different species of native wildflowers from the Maryland piedmont alone, but very few of the aliens. I love the natives so much, and find them so interesting, that I ignore the others.

But some of the aliens are rather pretty, and even if they’re weeds, they’re wildflowers, too. So this year I’m going to pay more attention to them, get good pictures, do the research, and feature them here.

There are at least four different species of flowers in the picture above. I can spot purple deadnettle, henbit, hairy bittercress, and one or two of the speedwells.


Call me a snob, but I’m just not interested in invasive alien plants.  I’d rather see a tiny, subtle native than a big, splashy exotic.  But there are times when they have their charms.


Like when this yellow goat’s beard (Tragopogon pratensis)
went to seed.

June 7






June 16



photographed at Belmont Manor and Historic Park, Howard County, Maryland