A knotty problem

It's raining again! Just as well we had a good long walk yesterday because it doesn't look like we will get one today.
Yesterday, we walked through Shipley Park, around the old American Adventure theme park, up onto the main road and along to Heanor where we had promised to help a friend with her market research (receiving payment in chocolate for our troubles - we're so easily bought). After that, we did a little shopping in Heanor, had a coffee at Tesco and then walked back home through Shipley Park. A round trip - inculding diversions - of around 9 miles.
Growing along the path, although not easily seen is this small plant, Common Knotgrass (Polygonum aviculare).

An unassuming plant with tiny, pink tinged flowers sprouting out of the axils of the leaves.

Used in antiquity as an expectorant, it was said, by Culpepper (the great 17th century herbalist), to cure the 'spitting of blood' as well as menstrual problems.
Much larger and far more obvious are the White Poplar trees (Populus alba).

One of the Aspen family, it is native to Spain, Morocco, Central Europe northward to Germany and Poland and into Central Asia. It is common growing on damp soils, especially beside streams and rivers.
The leaves display a thick, white/grey powdery coating, from which it gets it's name.

The whiteness of this tree is most obvious when there is a breeze to shake the leaves exposing their undersides which tend to be even whiter.