I usually associate Anomodon viticulosus with limestone, and it is certainly most abundant in VC35 on the Carboniferous Limestone of the lower Wye Valley and at lower altitudes around The Blorenge, but there are also plenty of colonies on riverside trees here. I assume that this results from silt deposition, also favoured by Orthotrichum sprucei.
A riverside patch of Anomodon viticulosus, and the species' distribution in Monmouthshire, with riverine populations (ringed in yellow) on the Usk, Monnow and Trothy, and limestone populations (ringed in green) around the coalfield, in the Wye Valley and near Usk.
I saw a large patch of Anomodon on the base of a mature Sycamore by the River Usk just upstream of Newbridge-on-Usk on Saturday, during my first (very brief) bryo-recording walk of the season. Orthotrichum sprucei was frequent, including on a Field Maple by the lane above the river (about 15m above the usual water level), and I also found a small population of O. rivulare (much rarer by the Usk than its relative). Leskea and Syntrichia latifolia were abundant, but Plagiomnium rostratum was remarkably rare and I found no sign of Mnium marginatum, M. stellare, Dialytrichia mucronata, Tortula subulata or Myrinia pulvinata (all present but rare alongside Monmouthshire's rivers). I was also surprised not to spot any Hennediella stanfordensis. It would be a very interesting project to compare south Wales' varied riverine bryophyte floras.