I agree that it looks like a clematis. If you didn’t pull all the roots it should regrow, if not this summer, then next spring. Provide it an obelisk or trellis to climb instead of the Dahlias.

ETA: The leaves on yours resemble those on my clematis Venosa violacea which is just starting blooming now. This was what it looked like a few days ago, but it has many more blooms now.

So yours could be this variety or one of many others. Often it is helpful to get an ID before ripping things out, both because it is easier for us to recognize plants in place, but also because sometimes you might have something worth keeping, especially if this is a new property.

Technu is a great product for gardeners and others to have on hand. It is a cleaner that will remove the urushiol oil from your skin. Works great. I live in the land of Wegmans so I just get it there but I believe Amazon carries it too.

And yes, not PI. Clematis are generally choice garden additions.

I'd keep an eye on it......not all clematis are desirable in the garden :-) Since you posted in the PNW Exchange forum as well, I'd assume you are located somewhere in this region. Clematis vitalba is a weed species here and pops up frequently. It is most obvious in winter when you see masses of tangled vines covering trees in natural or undeveloped areas and those tell-tale fluffy seedheads. Leaf shape is variable but often shows with the toothed, almost lobed margins. And it has dark, reddish stems.

Not sure where you might be located but poison ivy is extremely uncommon west of the Cascades. Occasionally one will encounter poison oak here but only in wooded areas or along some hiking trails. Might be found in some very rural properties that are more woody/native than groomed or cultivated.

Whew! Thank you. We are outside of Portland. It was definitely a tangled mess in the garden hiding under dahlias and boxwood. We are in a new house and are trying to clean up the garden quite a bit.

We have the native but weedy Clematis virginiana here. I dislike it.

I kind of like Clematis virginiana which is also native here, but in our colder climate it isn’t overly weedy. It’s always a matter of right plant and right place.

I quite like C. v. too Babs

It is very weedy here in western NC. Seedlings come up everywhere.

Yes the cold keeps it in check here and I find it only seeds directly beneath itself. For years I have only had it in 2 spots. One along my lane way where it scrambles along the split rail fence and the other in the garden at the drip edge of a sugar maple. Way too happy in NC apparently.

Seattle's Seward Park has climbing examples of poison oak 75 ft tall. Other Greater Seattle locations where this plant has been seen in later years include Lincoln Park, Beacon Hill, Normandy Park, Bainbridge Island and Vashon Island.

Much of historic regional distribution pattern (including Oregon sites) can be seen represented here:

http://www.burkemuseum.org/research-and-collections/botany-and-herbarium/collections/database/results.php?SourcePage=search.php&Lat=47.04&Lng=-120.8&Zoom=6&Polygons=&submit=+Search+&Classification=&Family=&Genus=&Species=diversiloba&Infraspecies=&Collector=&CollNum=&Day=&Month=&Year=&Accession=&Barcode=&Cultivated=&Origin=&Phenology=&TypeDesignation=&Country=&State=&County=&Locality=&MinElev=&MaxElev=&ElevUnit=ft.&SortBy=Year&SortOrder=DESC

Embo, I've seen that plant at Seward Park years ago near the entrance. It even had a label!