Researching houndstongue for the previous entry, I learned a new term, "ballast waif," for plants that cross the oceans in ships' ballast. In the days of sails and muscle power, ships were ballasted with layers of big stones, stacked carefully at the lowest point of the hull.
These stones were sometimes removed to make room for cargo and were just stacked to make breakwaters, etc. Now pumps fill tanks with water for ballast, and sometimes floating seeds (and zebra mussels) are sucked in, only to be flushed out later.
Lots of undesirable plants have arrived mixed with other seeds. I think that both tumbleweeds and kolchia came in with Russian wheat. This article explains the whole spectrum of hitch-hiking plants
Then there are "science heroes" like Frank Meyer. Back in the late 19th century, agricultural scientists looked upon the American and Canadian prairies and saw that they were bad. They were not "productive." They needed "improvement."
Hence, for instance, the institution of Arbor Day, a civic semi-holiday devoted to tree-planting. Kids were taken out of class to witness tree-planting on the school grounds: I remember that at Canyon Lake School, Rapid City, South Dakota.
Frank Meyer, a Dutch immigrant, was sent to Central Asia by the US Department of Agriculture to bring back "useful" species. He collected more than 2,000, making him either a science hero or a botanical Typhoid Mary, depending on your perspective. He drowned in an accident on the Yangtze River in China--or maybe some ethnobotanist shoved him overboard.
I grew up in his arboreal landscape. Siberian ("Chinese") elms in the Rapid City shelter belts and trimmed into a hedge in Fort Collins, Colorado--Frank Meyer.
"Persian" lilacs everywhere I have lived, including here-- Frank Meyer. Russian olives planted in our yard in Lakewood, Colorado, and considered a nuisance tree along the Rio Grande in New Mexico--Frank Meyer.
Honey locusts growing wild up Ute Pass from Colorado Springs--Frank Meyer.
And soybeans. Ask Roseann Hanson about soybeans.
The crested wheat grass in every bin of "dryland pasture mix" at the feed store--Frank Meyer.
A study by the Fish and Wildlife Service in 1993 of twelve species of birds endemic to the Great Plains discovered precipitous declines in their numbers over the past twenty-five years. . . . .The study blamed this decline on the conversion of grasslands to agriculture and the planting of crested wheat grass.
Richard Manning, Grassland: The History, Biology, Politics, and Promise of the American Prairie, 1995