With the consistent cold of late December/early January in our area, the flowering show of Christmas rose, Helleborus niger is lasting longer than is normal for us. These amazing evergreen perennials hail from Europe’s Balkan region. We find they thrive the best for us in very light shade or a couple of hours of morning sun, as long as the soil is well drained. This is one of only a few hellebore species with naturally out-facing flowers.

These have done well for me, perhaps too well, as I am giving lots away.H. niger is not as invasive a H lenten.
There are no hellebores that fit any meaningful definition of invasive. Helleborus x hybridus, are, as you indicated, prolific seeders, but only near the parent plants. We have 35 year old patches of Helleborus niger, but we’ve never had enough seedlings that any needed to be removed.