32 year old moss mystery solved! Pleurozium schreberi.

Letting a leaf slide dry overnight really makes the structures easier to see. I might have used KOH on this too. I was about to give up on ID of this moss,  I only have tiny scraps of it, don't know what it grew on or even if it is an acrocarp or not.  But bryonet came to the rescue and I now have an ID for this.

Pleurozium schreberi

Leaf: 1.5mm x .5m , mid leaf cells 80um x 5um

stems about 1cm, Springer Lake Bog

Here is a fresh Pleurozium schreberi leaf from my collection