Yes - Lythrum salicaria aka Purple Loosestrife. An invasive species in much of N America, I'm afraid.http://www.invasiveplants.net/plants/purpleloosestrife.htm

Please don't plant it. It spreads through seed, often miles from where the plants are when birds carry the seed on or in their bodies. It is a major problem in wetlands in much of the US and Canada. Some alternatives that share some similarity of shape or size or bloom time or color include Liatris (gayfeather), tall garden phlox, hybrid Verbascums (Mullein), Agastache (hummingbird mint), foxgloves, Gaura, Penstemon, many Salvias, or some of the taller Veronicas.

I think some of what was previously written about purple loosestrife lacked substantiation. Past surveying on-line and contacting university sites, I found almost no reports of purple loosestrife cultivars losing their self-incompatability and/or seeding in actual garden situations. I did see one report from a gardener, but his seedlings subsequently died in location.

Below, however, is evidence of a plant, purchased as the cultivar 'Rosy Gem', seeding in a real garden; namely, seedlings from that plant. This garden is in a residential subdivision with no "wild" purple loosestrife close nearby. The possibilities does exist that 'Rosy Gem' had not been selected for self-incompatability or that the plant originally purchased was not really 'Rosy Gem'.

I'm assuming that the presence of a sprinkler system was a factor, since the system was malfunctioning and the seedlings were growing only in a very wet location that resulted.

Tip: If removing purple loosestrife, it easily relocates itself to a compost heap.

Personally, I think it would be disingenuous to claim that any equally showy substitute perennial is available here for purple loosestrife. I'd say it's a beautiful plant and the bees love it.

On the other hand, horticultural purple loosestrife must be continually watched for seeding and therefore it's maybe preferable to just remove it.

Picture November 7, 2011. Some of the seedlings have already been removed to expose others. There is no purple loosestrife in that garden now.

SunnyBorders - I have no personal experience of PL being invasive. It's native here and actually not that common. But I have read many statements on GW that it is and there many reputable sites stating the same. We don't know what version of PL the OP is likely to obtain if they go ahead and purchase. I was just warning them. http://www.issg.org/database/species/distribution_display.asp?si=93&ri=18909&pc=*&sts=&status=Alien&lang=EN#Alien .

SunnyBorders Does your area not have a problem with it? Here in rural Eastern Ontario it is rampant.

The research station in Morden Manitoba had developed some named varieties of Lythrum salicaria many years ago and I was sure they had been prohibited from sale. Double checked and sadly they are. Here is a link Lythrum salicaria

Floral, you are right to warn gardeners about using any forms of purple loosestrife here (horticultural as well as wild) in gardens.

Perennials.all, I do have a good idea of the distribution of wild purple loosestrife in Ontario and elsewhere in North America. I think you missed the point of my post.

The 1992 Manitoba Study took plants of the horticultural cultivar 'Morden Pink' and planted them near a river and adjacent to wetlands, both of which had wild purple loosestrife present. The furthest any of the cultivar plants were away from wild purple loosestrife was 200 meters.

'Morden Pink' was thought to be sterile. It was presumed that the ability of plants of the cultivar to self-fertilize themselves, in the way the wild type does, had been bred out of them; namely that they were "self-incompatable".

In fact, it was found that the cultivar plants lost their self-incompatability (hence sterility) in these locations in the presence of the wild type and, like the wild form, produced very large numbers of seeds.

Some gardeners then wondered whether there was any evidence for sterile purple loosestrife cultivars losing their self-incompatatbility in garden situations, when the gardens were located nowhere near wetlands nor wild-growing purple loosestrife.

Some simply dismissed this question out of hand. Either you believed in "the purple plague" or you didn't.

Personally I'm more impressed by evidence. Are the researchers correct in extrapolating from purple loosestrife cultivars placed in research locations to those in average gardens? Over the years, I've seen almost no relevant evidence presented by gardeners.

My post presents such evidence; that is seedlings which have been produced by one plant of a horticultural purple loosestrife cultivar that lost it's self-incompatability in a garden.

When I was a child in the 50s, we had a summer place in Dutchess County, NY. Acres and acres of swampy land were covered with purple loosestrife. As city folk, we thought it was a native. Recently it has begun to appear in ditches in West Virginia.

Years ago I planted seedlings of a hybrid form of Lythrum salicaria in the garden. They self-seeded very scantily. Unfortunately the Japanese beetles loved them. There may be a remaining solitary plant remaining in an out-of-the way spot.

Liatris is often mentioned as a good substitute for Lythrum, but it really can't match its ornamental performance in my opinion. Long-flowering Salvia hybrids are a better bet.

"Self-seeded very scantily" that's precisely what I've seen, Rusty.

I wonder whether supposedly infertile garden purple loosetrife cultivars need to be within pollinator range of free-seeding wild plants to occasionally lose their self-incompatibility.

I haven't planted any purple loosestrife for years. However, it always annoys me when people imply that there are equally attractive garden substitutes here for horticultural purple loosestrife. I agree with you, for instance, about Liatris.

At the same time, Liatris is a great garden perennial. I've used a lot of 'Kobold', which I find a particularly attractive Liatris cultivar. I also do agree that one may well get more and longer (with dead-heading) colour from a number of long-lived perennial Salvia cultivars (species or hybrids).