Identification notes

This is an uncommon species of damp and wet heath in Britain, forming small localised patches in open unshaded habitats. It is typically a yellowish or brownish green and has regular pinnate branching. Closer inspection will reveal the characteristic brown stems. It usually grows close to Hypnum jutlandicum and care needs to be taken to separate the plants. Hypnum jutlandicum is typically a rather washed-out pale green colour, and the less regular branching gives it a more scruffy appearance. The stems of H.jutlandicum are green rather than brown, but sometimes one comes across plants with some sections of the stem that are brown, possibly due to staining by immersion in peaty water. If there is any uncertainty then microscopic examination is required.

The simplest character is the appearance of the alar cells. In H.jutlandicum they are usually scooped out to form a sac which is best seen using a stereo dissecting microscope. They tend to have particularly inflated cells at the extreme angles. In H.imponens the alar cells lie in the same plane as the leaf and are not so inflated.

Examining the pseudoparaphyllia can be challenging but provides important confirmation. These are tiny fragile leaf-like structures that are formed at the base of branches in Hypnum species. A good way to find them is to dissect off the stem leaves at the base of a branch, then pull off the branch and sever the stem just above and below where the branch had joined, and then transfer the small stem section to the compound microscope. The pseudoparaphyllia  of H.imponens are clearly toothed, whereas those of H.jutlandicum are untoothed.

Distribution in Great Britain and Ireland

Although a widespread plant in the USA and Scandinavia, it is curiously restricted in Britain and is unknown from Ireland. Most records are from the heaths of Southern England, and the far north of England and the Scottish Borders.