Acrocarp vs Pleurocarp

True Mosses are usually divided into two large groupings: Acrocarps and Pleurocarps:

ACROCARPS have capsules at the tips of their branches. they grow erect, simple or sparsely forked and often cluster in tufts or cushions. Acrocarps generally have a single costa, erect capsules and short leaf cells.

Polytrichum commune

Dicranum scoparium

Ulota crispa

PLEUROCARPS have capsules coming off a side branch.  They usually are freely branched and grow in interwoven mats. Pleurocarps generally have long cells, short and double costas, and curved capsules.

Callicladium haldanianum

Hypnum imponens

Abietinella abietina

Callicladium haldanianum