This "smart" weed, which I believe to be Polygonum pensylvanicum L. or Pennsylvania smartweed, adorns itself with pretty flower tufts. It volunteered in my bird and butterfly garden but I moved it to my more "wild" area towards the back of my shed not knowing exactly what it was at the time. It transplanted well and this fall looks quite stunning.
The flowers attract long-tongued bees, short-tongued bees, wasps, flies, small butterflies,
skippers, and moths. Smartweed plays host to several moth caterpillars, including
Lithacodia synochitis (Black-Dotted Lithacodia), Lithacodia
carneola (Pink-Barred Lithacodia), Haematopsis grataria (Chickweed
Geometer; often flies during the day), and Dipteryia rosmani (Noctuid
Moth sp.). The caterpillars of the butterflies Lycaena helloides
(Purplish Copper) and Strymon melinus (Gray Hairstreak; eats flowers and buds) are occasionally observed on smartweeds as well.
Many birds eat the seeds: waterfowl, gamebirds, and songbirds. I do not see many waterfowl or gamebirds in my village garden although they are nearby. Songbirds that Smartweed might attract to my garden include the Cardinal, Redwing Blackbird, and a great number of Sparrows – Grasshopper, Savannah, Swamp, Song and Tree. In the winter Juncos will eat the seeds.
The foliage and flowers stand up well. I like that this plant is still blooming at this time of year. I think some Goldenrod mixed in with the Smartweed would be a nice combination.
Consider letting Smartweed star in your flower garden if it happens to volunteer. The birds and bugs will appreciate it and I think you just might appreciate the late fall blooms as well. Also consider Smartweed if you have a pond or wetland area in your garden and wish to attract waterfowl. It does prefer a moist soil. Seeds are available for purchase from Prairie Moon.
Sources: Illinois Wildflowers, USDA Plants Profile, Lady Bird Johnson Wildflower Center