“What are you going to write about this week?” asked Jane.

“Late summer and fall wildflowers,” I answered.

Next day, I passed a shimmer-topped thicket of perennial Japanese knotweed. It was pretty, but I knew it for the thug it is.

Japanese knotweed, botanically Fallopia japonica, was introduced into the Netherlands in 1849, and was originally used in gardens as an “architectural” plant. In some gardens, it’s still part of the landscape.

In Japan, it’s not often seen; in this country, it lives and spreads happily when introduced, nudging out other plants. It doesn’t do well in dense shade.

Underground, its roots strengthen and intertwine. Dig it out and any piece left in the soil will grow a new plant. Throw it away, and those pieces drift in bodies of water until they find dry land, where they’ll settle in for a new colony.

Japanese knotweed, also called Mexican bamboo, can grow a bushy six feet tall. Bees love the flowers; beekeepers harvest the honey.

In early spring, some people use the young shoots and leaves as a cooked vegetable; it’s like sour rhubarb. In fact, some people pickle the shoots. Anyone with arthritis, gout or kidney problems can skip this dish as it contains oxalic acid. It’s also laxative.

Hard to kill, foraging goats can keep Japanese knotweed at bay. Maybe, if it were pitted against European bittersweet (Celastrus orbiculatus), the two invasives could overpower each other?

Many of goldenrod’s 50-plus species have stayed unusually late this year, brightening many an old field and hillside. These wildflowers also weave roots together to save the land for themselves, which is why some old meadows are not bothered by encroaching forests.

(I’ll say it again: goldenrod’s heavier pollen won’t bother allergies. Ragweed, its cousin, is the culprit: it has lighter, wind-driven pollen.)

Right now, starry, white wood asters are blooming along with the goldenrod, usually along the edge of woods. Next week, I’ll be back with more autumn perennial beauties.