I figured. Sounds like it spreads like the alder and willow around here!Now a tree that you can no longer buy. So many states have declared them a noxious weed that the nurseries no longer grow them for sale.
You betcha, I got most of mine by simply watering areas and everywhere that got watered they sprouted from all the seeds that the birds crapped out.
Granted, the alder and willow don't typically spread through seeds.