Identification notes
One of three similar-looking taxa that have sometimes been grouped as the ‘Racomitrium canescens aggregate’, R. elongatum is now considered distinct enough to merit recognition at species rank. This species, R. canescens and R. ericoides differ from our other Racomitrium species in habit, forming short turfs rather than tufts or cushions on the ground (less often on rock). They all have matt-looking hoary leaves and stems with numerous, short stubby branches. They are also slow-growing, weakly competitive species that favour dry, barren ground that dries out periodically, such as on gravelly tracks or dry mineral soil in disused quarries.
Of the three, only R. elongatum and R. ericoides have a nerve which clearly reaches into the leaf tip. R. ericoides is much the commoner species but it’s always best to check candidate material to rule out R. elongatum.
In the field, obviously long hair-points that are decurrent down onto the lamina and reflexed when dry are useful pointers to R. elongatum, but just to confirm, make sure you check for short, thick-walled marginal cells just above the alar group under a microscope. 💡 These cells are at the extreme base of the leaf and often remain attached to the stem when leaves are pulled off with forceps. Find leaf bases with intact alar cells (enlarged, egg-shaped non-sinuose cells) and look at the margin immediately above to confirm the identity. There are some good images below.
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