Cosmopolitan Weeds--Friends of the Botanical Traveler

Victoria, Australia

Thousands of miles from home, surrounded by plants strange to me, I am delighted to see a plant I know.  Look, a dandelion!

dandelion, Taraxacum officiale

They probably are weeds to the people who live in Australia, just as they are in Colorado, but surrounded by unknown plants, the dandelion looked like an old friend.


There are some 400,000 plants in the world, many more if you count the thousands of varieties of cultivated plants, whether they are rice, apples or orchids. Stay close to home and you can learn all about the few hundred plants you see regularly. But travel across an ocean or the length of a continent and you can't take much for granted. Sometimes whole plant families are new: there are no plants in the big tropical families Melastomaceae or Arecaceae (palms) in northern Colorado. (Outdoors, that is, both families include some house plants).

melastome, Melastomaceae

palm

But even when I recognize the plant, in the sense that "that looks like a willow" if I'm in New York or Oregon, let alone England or Argentina, it is likely to be a different species of willow, not the same one that grows where I live. Most plants have only a regional distribution.

Humans have confused nature's regionalism by growing some plants all over the world: apples and daffodils, for example. But the experienced botanist is wary of even the cultivated plants. It might be an iris, but there are irises native to the US southeast, Europe, Japan and South America, at least. So it is an iris, but likely a local iris, so who knows what species. "Everyone" grows irises, but not necessarily the same irises. The same applies to many plants.

variegated European iris

Iris lactea, from China

But the cosmopolitan weeds? There are a few species that have gone all over the world and it really is the same species that I saw at home. It is not a long list, because although humans make aspects of urban or rural life similar, that does not change the basic climate. Few plants can grow in both the three month growing season of Steamboat Springs, Colorado and year-long warmth and abundant rain of Miami, Florida.

In urban temperate regions, look for dandelions, plantains (Plantago major, P. lanceolata), curly dock (Rumex crispus) and sheep sorrel (Rumex acetosella), common mullein (Verbascum thapsus), lamb's quarters (Chenopodium album), shepherd's purse (Capsella bursa-pastoris), and maybe chicory (Cichorium intybus) .

plantain Plantago major

But that's about all.

Weeds are plants that interfere with human activities, that are "in the wrong place." Ruderal is a term for plants of roadsides and other human-disturbed areas, whether they interfere or not. This short list of "cosmopolitan weeds" are plants not really interfering (much) nor ruderal, but rather specialists at urban and suburban settings. They are plants that get around easily (therefore they reach diverse places), like to grow in conditions created by humans such as lawns, and tolerate a wide range of temperatures, soils, rainfall patterns (etc.). Thus they can grow in chilly lawns in Scotland and warm humid parks in Georgia.

chicory, Cichorium intybus

But there are limits, most of these are not found in the tropics. Look for them there. You'll likely see other roadside and lawn weeds.

Because it is such a big, complex world, it is no surprise for a Coloradan not to recognize the plants in San Diego, California, Melbourne, Australia or Florence, Italy. The surprise is in seeing a plant you really do know.
.
And so. met in a distant location, they aren't annoying weeds, they're old friends.

Watch for weeds you know all over the world and consider how far they must have come and how different the conditions are between the places you've seen them. Pretty remarkable plants.

shepherd's purse, Capsella bursa-pastoris

Comments and corrections welcome. (What cosmopolitan weeds did I forget?)

Kathy Keeler, A Wandering Botanist

More at awanderingbotanist.com

Join me on Facebook: https://www.facebook.com/AWanderingBotanist