Creeping Bellflower

This beautiful, delicate-looking plant is serious trouble. It’s been described as a hellcat, unruly and horribly invasive. “If it has a weakness I am unaware of it,” says one author, using a tone normally reserved for zombies.

Creeping Bellflower (Campanula rapunculoides) was brought here from Europe because it’s a beautiful garden plant. It is also adept at surviving in urban and cultivated areas. It can squeeze through even the tiniest cracks in the pavement. You can’t kill it by yanking it up, because it can regrow from the smallest pieces of root left in the ground. Its deep and powerful root system can’t be eliminated by mere mortals.

To identify Creeping Bellflower, look for stalks up to 3 feet high with blooms on one side of the stalk. The flowers are bell-shaped and open into a five-pointed star. There are some local native bellflowers that look a little bit similar, but none is as spectacular, and none will colonize sidewalk cracks in the same aggressive way. Before the flowers have arrived, the plant is low to the ground and inconspicuous.

Most weed guides suggest destroying Creeping Bellflower with powerful chemicals, or digging up the entire affected area, including a substantial buffer zone. Alternately, you can sit on your porch and watch the purple flowers sway in the breeze, resigned to a life under the control of your beautiful bellflower overlords.


July 2, 2010 at 4:02 am 2 comments

White Clover

When kids hunt for four-leafed clovers, they’re usually searching through the clumps of White Clover (Trifolium repens) that blanket our lawns and parks. It’s hard to believe that a plant this common in our cities was absent from North America just a few hundred years ago. It’s yet another species that was brought here by European settlers.

As with many weeds, White Clover blurs the boundary between pest and friend. It spreads so well that it can displace native plants. However, White Clover is a member of the pea family, and like many of its relatives it performs an invaluable service.

Plants need nitrogen to grow — as do people, since without it we’d have no protein and no DNA. Unfortunately, the nitrogen floating around in the atmosphere is stuck in a form that’s useless to most living things. The roots of White Clover have round nodules that provide ideal housing for special bacteria, and these bacteria turn atmospheric nitrogen into useful nitrogen.

White Clover is a nutritious food for livestock and for wild browsers like deer. It’s a good plant for a lawn because it doesn’t need much mowing. Also, when insect pests destroy the grass, White Clover eagerly fills in the blank spaces.

So why call it a weed? Shockingly, there’s some evidence that White Clover might have been the victim of a slanderous marketing campaign in the 1940s. Companies that developed herbicides for lawns weren’t able to create a mixture that would spare White Clover but eliminate other weeds, so they declared it a weed, too. Innocent helper or nefarious invader? Our lawns are full of complicated characters.

June 29, 2010 at 12:55 am Leave a comment

Sensitive Fern

Ferns can seem pretty unremarkable at first. They don’t have spectacular flowers — in fact, they don’t have flowers at all. They’re kind of like a bass player in a band; they’re subtle and unassuming, but absolutely critical and really cool, and everything is just tacky without them.

Ferns are very ancient. They dominated the land long before the dinosaurs. As a result, their reproductive cycle is weird and somewhat primitive. They produce spores, and these develop into a romantic heart-shaped structure that has both male and female sex organs. With the help of water, sperm swim from the male part of the structure to the female part, and this union produces the baby fern. Flowering plants eventually overshadowed the ferns because they figured out how to get it on without this lubricating water.

The Sensitive Fern is found in the eastern half of North America, and also in East Asia. It’s a good fern to learn first because it has a unique look. It’s bright green, and it has a “rough” shape, as if a kid did a sloppy job of cutting it out of a piece of construction paper. It keeps its spores in a separate brownish leaf that appears in about July.

Early European settlers in North America gave the Sensitive Fern its name because it shrivels at the first hint of frost. It also has demanding needs in terms of moisture and shade. But the Sensitive Fern makes up for this sensitivity by packing powerful toxins that can seriously harm any animal that decides to take a bite.

In the urban environment, the Sensitive Fern is often found in shady gardens, playing steady bass to the electric guitars and trumpets of the flowers, and lookin’ cool.

June 26, 2010 at 6:21 pm Leave a comment

Lady’s Thumb

This post is late because I’m busy moving to a new city. Fortunately, today’s plant can be found in almost any American city, eking out a living in the tiniest cracks between pavement slabs.

Lady’s Thumb (Persicaria maculosa) is a member of the Buckwheat family, and it counts rhubarb and buckwheat among its more illustrious relatives.

This plant is native to Europe. I don’t know if it was brought to North America because it was edible (though your mileage may vary) or because of its purported medicinal qualities, or if its tiny black seeds hitched a ride in a shipment of grain. Regardless, it found the New World to be very inviting.

This tough little plant now thrives deep in the concrete jungle. I remember coming across one of them when I was five years old and living in Philadelphia; it was protruding improbably from a little rift in the pavement outside my home. I puzzled over the clump of bubblegum-pink beads that were, it turns out, its flowers.

The name Lady’s Thumb comes from a spot on the leaves that supposedly looks as if a lady pressed her (very dirty?) thumb against it. This spot helps distinguish Lady’s Thumb from some of its relatives that are native to North America.

I’ve been focusing on non-native plants on this blog so far; the truth is that the world of urban botany has as much to say about the travels of humans as it does about plants. Still, I promise to feature a native plant on Friday. There are native plants in the city, jostling leaf-to-leaf with Lady’s Thumb and all the rest.

June 23, 2010 at 1:43 am Leave a comment

Norway Maple

There may be an imposter living in your backyard.

Full disclaimer: I grew up in Canada, and I’ve always been a sucker for the Sugar Maple tree. Its leaf is found on our flag and everything else that is patriotic. But people in the US Northeast also love this tree because it provides the sap for maple syrup. (This sweet quality is reflected in its Latin name, Acer saccharum.)

So I was surprised to learn that many of the “Sugar Maples” lining Canadian and American streets aren’t Sugar Maples at all. They’re members of a look-alike species from Europe called the Norway Maple, Acer platanoides.

The Norway Maple was brought to North America in the mid-1700s. It was a popular garden tree; even George Washington was thrilled to score himself a couple of Norway Maples for his yard. In urban areas, it proved to be the ultimate secret replacement for the beloved Sugar Maple because it was much more tolerant of pollution, road salt and denuded soil.

Unfortunately, the success of the Norway Maple came at a price. It spread into natural areas and displaced native plants (including the Sugar Maple). Its leaves were just a smidgen bigger, and its foliage just a touch thicker, and native seedlings couldn’t grow in its thick shade.

Nowadays it’s considered a dangerous invasive species. Some states have even banned people from planting them.

How can you tell that Norway Maple from the Sugar Maple? There are several subtle clues, but my favorite way to distinguish them is to pick a leaf and snap the stem. Only Norway Maple will exude a milky white sap. Of course, you could always just compare its leaf to the one on a handy bottle of ice cold Molson Canadian beer. Cheers!

June 19, 2010 at 2:52 am Leave a comment

Bladder Campion

Bladder Campion was blessed with one of the least graceful names in the plant world, right up there with Pale Swallowwort and Clammy Ground Cherry.

Like many of the flowers in our cities, Bladder Campion is not native to North America. European settlers brought it to the new world for their gardens. This plant took readily to waste spaces, spreading gleefully into gravelly roadsides and abandoned fields.

Several other Campion species were also brought over from Europe. To distinguish this one from the others, note that Bladder Campion has the most impressive, well, bladder (the green tic tac-shaped object just below the white petals), and other Campions have hairy bladders. As an urban botanist, it’s your duty to loudly point out facts like this to your friends, especially at parties.

When I was a kid, my friends and I used to torment these plants by holding the bladders shut to trap air, and then clapping them with our hands so that they would make a loud pop. (Plant nerds: the inflated-looking part is called the calyx, the modified leaves that enclose a young flower.)

This flower will be blooming until September, so keep an eye out as you walk down the street. The Latin name for this flower is Silene cucubalus.

June 13, 2010 at 11:50 pm 5 comments

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