You may laugh, but Japanese knotweed young plants and lilac plants look annoyingly similar. I have had many photos of lilac from concerned people thinking it may be Japanese knotweed in their garden.
The plant on the left (closest to my boot!) is Japanese knotweed. You can see the typical reddish colour to the stem. On the right is a small lilac plant and it lacks the reddish tinge to the stem, but at a quick glance it's easy to see how people do get the two plants mixed up.
Feel free to text/email a photo of any concerned plants you may have and I will do my best to confirm if it is or isn't Japanese knotweed!