Square Gooseneck Moss

Rhytidiadelphus squarrosus grows as an extensive mat of branching stems, up to 15 centimetres (6 in) tall, sheathed in leaves that are 2–2.5 mm (0.08–0.10 in) long and bend sharply back at a right angle, and thus spread outwards from the stem. The leaf bases are broad and include a pair of short nerves. The plant rarely produces capsules, so most of the species' reproduction is asexual.

Rhytidiadelphus squarrosus has a circumpolar distribution in the Northern Hemisphere, being found across much of Eurasia, and parts of North America, including British Columbia, Alaska, Washington, Oregon, Newfoundland and Labrador and Greenland. It has also been introduced to northeastern North America, Tasmania and New Zealand, where it is now an invasive species. The first specimen to be collected in the Southern Hemisphere was taken in 1974 in Dundas Creek, western Tasmania, but the first published record came the following year, from a golf course in Dunedin on New Zealand's South Island.

It tolerates a wide variety of soil conditions, from calcareous grassland to acid heaths. It grows most conspicuously in heavily grazed pastures and on the regularly mown fairways on golf courses, and is the most common moss found in lawns in the United Kingdom. It is almost always found in association with humans, leaving its original habitat unclear; it may have evolved as a plant of coastal meadows.

The genus name Rhytidiadelphus derives from the words Rhytidium and ἀδελφός (adelfós, brother), implying a close relationship to the genus Rhytidium. The specific epithet squarrosus refers to the leaves, which are squarrose, having a right-angled bend which causes the tips to extend away from the stem.