This is the delicate little seed of a large bamboo-like plant called variously, false bamboo, or Japanese bamboo. It isn't a real bamboo, being in a completely different family. It was classified in the genus Polygonum, but has been recently moved into the genus Fallopia. It is a highly invasive species, more so out west in BC's Lower Mainland. But even here, it can form dense thickets that spread further and further each year, shading out all other plants.