Last week, we had observed an abundance of this plant and I had another look at it. I'm now pretty sure it is cleavers since it's stem is very scratchy.
We continued working on garlic mustard but it's really the last time we can try to pull it as it's getting really tall and hard to remove without breaking it.
It is particularly hard to get the roots out.
But with perseverance, it is possible to get the whole thing out with the roots which can be quite long.
Blue Flag Iris, one of the native flowers along the pond.