Persicaria pensylvanica

Pennsylvania Smartweed

• Annual
• Full sun to part shade
• Average to high moisture conditions
• Grows 24" to 48" tall and 12" to 36" wide (larger sizes in rich soils with lots of sun a nd moisture)
• Ontario native species, does well in containers

While Persicaria that look a lot like these are not uncommon in disturbed areas (ditches, field edges etc.) locally, I knew just enough about Persicarias to know that there are both native and invasive species, and I didn’t want to accidently gather seeds from an invasive species, so I purchased seeds from Prairie Moon Nursery to be sure which species I was planting.

A large part of my interest in planting these came from the fact that they are a relatively fast growing, long blooming native annual. Something that made me think that they might be good candidates for container gardening.  The test planting, in a container in full sun and another in part shade, last summer was a success. They thrived, blooming through the summer and into the fall.

Despite the very tiny size of their blooms, they attracted bees of a variety of sizes, from tiny metallic green sweat bees to big fuzzy bumblebees. From an ornamental standpoint, their long bloom season is further bolstered by the fact that the seed heads retain their pinkish colouration, rather than browning, as the shiny black seeds mature within them, creating an even longer lasting impression of colourful flowers. The seeds are relatively large and a significant food source for many bird species. If you are gathering seeds for saving or sharing, keep your eyes open for heads that are still pink or green, but that seem to be dropping ‘flowers’ these are actually clusters mature seeds inside individual, tightly fitted, not-dry wrapper. If you gently brush the seed heads over a container at this stage the ripe seeds will easily drop off. If you rub the seeds firmly the thin skin will come off and you will see a single, shiny black seed.

Now that I’ve had a chance to see the native species close up, I started looking through images of the Persicaria species that have been introduced, some of which have become invasive in this region in an effort to learn to distinguish them from the native. Of the invasive species, Persicaria maculosa, Spotted Lady’s-Thumb and Persicaria orientalis, Oriental Smartweed (Please pardon the Oriental bit, it is currently the official name), bear the strongest resemblance to this species. The first isn’t too difficult to distinguish once mature, since they develop fairly prominent dark patches on their leaves, presumably the source of their common name. The second was a bit more challenging to sort out. I finally came across a distinguishing feature. The ocreae on the native Smartweed are non ciliate and the ocreae on the introduced species are ciliate.  Clear as mud?

Further Googling.

Ocreae are a papery sheath that can be found at stem junctions and ciliate describes a hairy looking edge. A lot of gardeners will have seen ocreae on the flowering stems of rhubarb plants, where they appear as a thin wrapping where leaves and flowers branch off the main stem, that starts out green and often dries to dark brown. So, when examining a plant that looks a lot like the ones pictured here, check where branching stems meet. If the thin papery membrane you see there has a smooth edge, you are looking at a native species, if it has a hairy edge, it is the invasive species.