It is not knotweed......and it does look like a tree seedling (root shoot), what type I am not sure. But you will get faster and accurate ID's if you use the forum - Name That Plant - that is intended for plant identification. This is not the right place :-)

Jerzeegirl, it may be a Giant Dutchman's pipevine but I'd guess littoralis Elegans. Love their flowers. If the flowers are a foot long or more, it's definitely a Giant. Elegans flowers are about the size of your open hand. And, as Sharon said, pipevine swallowtails love pipevine. But, and I may be wrong, while pipevine swallowtails will lay their eggs on Giant Dutchman's pipevine, the plant is too toxic for the caterpillars and they will die. Pipevine swallowtails can use pretty much any pipevine except Giant. When I was in north central Florida the pipevine swallowtails used the native pipevine that grew wild on my property. However, Polydamas aka Goldrim swallowtails use Giant, Elegans and other pipevines as host plants. I've raised tons of Polydamas using Elegans. This swallowtail is pretty common here in SW Florida. Here's a few pics I took to help you identify them. Sorry that I don't have a picture of the butterfly from above but it's black with a gold band across the hind wings. Good luck!

cut it to the ground.. and apply a stump killer ... its too close to the house ... and with the size of the trunk ... moving it would be very hard ... plus digging that close to the house ... ken

Parker: That is a much better image for ID, showing all body segments and antennae. It has Flower Chafer (a Scarab beetle) written all over it. My initial impression of the first image was a tick! (wrong leg count) https://bugguide.net/node/view/4468 (see Identification sentence) @jinx: If the image reminded you of E. basalis off the top of your head, you are much more familiar with beetle species than I am! E. basalis has only one image submitted to bugguide and its US range is just Texas. I did do a thorough search of all the Euphoria species, and some did look similar to the Parker image. Your correct subfamily ID did help narrow the search. I do prefer Valgus hemipterus (suggested above) for the ID. https://bugguide.net/node/view/410352/bgimage (the 4 black patch alignment on the lower abdomen is quite distinctive) The Info and the Data tabs on the above link will be of particular interest to Parker.