Polytrichum commune • Common haircap moss

Familia: Polytrichaceae  →  Genus: Polytrichum  → Species: Polytrichum commune

Genus name: Polytrichum  (Polytrichaceae) スギゴケ属 • sugi goke  (literally: cryptomeria moss)

About genus: Polytrichum mosses are called called haircap moss or hair moss (also called pigeon wheat mosses, per Encyclopedia Britannica). They often form large mats in peat bogs, old fields, and areas with high soil acidity. The Polytrichum is distributed globally, contains between 40-100 species, with about 10 species found in North America.

Scientific name is derived from the Ancient Greek words polys, meaning “many”, and thrix, meaning “hair” – so it gets its name from the hairs that cover, or cap, the calyptra where each spore case is held.

Species description: Polytrichum commune •  ウ マスギゴケ • Osugi goke  (literally: Great cryptomeria moss).  In Japan it grows on Hokkaido, Honshu, Shikoku, Kyushu.


2/4/17 – Polytrichum commune – wiry green stems with long stiff leaves, also brown old ones

Also known as common haircap, great golden maidenhair, great goldilocks, common haircap moss, or common hair moss. It is the most widely distributed species of the genus, found in many regions with high humidity and rainfall.

It is a medium to large moss – the erect stems are most typically 5 to 10 cm height, but can be as short as 2 cm or as long as 70 cm, with pointed leaves arranged spirally around the stem. It is dark green in color, but becomes brownish with age. The stems can occur in either loose or quite dense tufts, often forming extensive colonies.

Habitat: Preferring to live in lightly shaded areas with moist slightly acidic soil, P. commune can also survive in areas of full sunlight provided the soil is moist.  The Common Hair Cap Moss can also grow in areas of poor soil and slow drainage.


SJG • 4/22/16 – P. commune on the back of machiai, Area W – note its conspicuous height

Distribution: One of the most common plants found around the world, Polytrichum commune grows natively on almost every continent, in a diversity of habitats , even in Africa, where it occurs in forest, grassland and savanna (see the link below for the Pretoria National Herbarium write-up).

There are 4 species of Polytrichum growing in WA state – P. commune, P. juniperinum, P. strictum, P. piliferum and 3 related Polytrichaceae mosses – Polytrichastrum alpinium, P. sexangulare , P. formosum.


SJG • 4/22/16 – close up of the above photo on the back of the machiai

The last two mosses used to be classified as polytrichum, and Polytrichastrum alpinium was Pogonatum alpinum prior to being placed in Polytrichiastrum, although it was originally placed in Polytrichum by Hedwig (upon whose work moss classification was based in the early 1800’s). The classification continues to be fluid: […] The genus Polytrichastrum was separated from Polytrichum in 1971 based on the structure of the peristome (which controls spore release). However, molecular and morphological data from 2010 support moving some species back into Polytrichum […] (wikipedia)

SJG notes: Common haircap moss grows in many places in the Seattle Japanese Garden – mostly in the Tea House Garden (area W), but tall and dense colonies also appear in Areas Z, S and along the East path.


SJG • 11/8/16 – P. Commune under the tree in Area W -when its brown to reddish-brown capsules are present, the moss appears to bloom

One of the showiest mosses with a distinct appearance, P. commune is easy to spot in our garden: it is our tallest moss that grows upright, have dark green and wiry stems and long, stiff leaves.

There are many quite poetic descriptions of that moss in the bryo-literature (star-like, fireworks, etc.), but as seen from the path in the SJG it is mostly its height that is noted + very distinctive brownish ‘bloom’ when the sporophytes are present (about half of the year).

The Japanese culture has about the longest history of appreciating the world of mosses since they naturally occurred around the shrines and temples some 10 centuries ago. The monks/priests not only let the mosses stay as part of the natural environment, but soon also took upon themselves making the mosses welcome by clearing them from debris and fallen leaves.

Sugi goke moss became one of the most prized mosses in the gardens and temples because to the Japanese eyes the moss looked like a mini-cryptomeria (Japanese Cedar) – a beloved since primordial times tree known as “sugi”, which to this day is the national tree of Japan.


SJG • 10/18/16 – P. Commune around the tree stump in W

The cryptomeria tree was exceptionally important in the ancient Japanese society  as a building material but also for its spiritual meaning.  Both traditional and modern Japanese culture highly regards natural objects: the Shinto religion represented a connection between man and nature and tall trees had a special import – Japanese cedars are found at the center of many Shinto shrines.

As for the Sugi tree’s mini-counterpart, for the most Japanese people it’s simply a short (sugi goke) or a tall/great (Osugi goke) cryptomeria moss.  According to western taxonomy there are, in fact, about 4 or 5 different species of polytrichum moss commonly named sugi: some short, some tall, depending what type of moss naturally grows in that part of Japan (they all look very similar).

Luckily for us, the Seattle Japanese Garden has only two of those mosses, so no confusion: P. commune works as the tall cryptomeria (Osugi goke), and P. juniperinum works as the short cryptomeria (sugi goke). Years ago our gardeners purposely cultivated P. commune to strategically plant it around the garden, and now there are new plans to do so again, as the colonies became somewhat destroyed with time.

Polish genus name: płonnik


References and related reading:

• Good general write-up of the P. commune from the Toronto, Canada, Tree of Life web project

• Interesting comparison of P. commune and P. juniperinum (we have BOTH in SJG) from Ontario, Canada, borealforest. org

• Pictures and descriptions of P. commune from NatureSpot in England

• Ohio university good write-up on P. commune

• Notes from Pretoria National Herbarium describe how in southern Africa P. commune frequently grows on gravelly soil and steep banks of road cuts, and on soil among grass along stream banks – from Limpopo, to KwaZulu-Natal, to Swaziland and Lesotho

• Tour of mosses at Yakushima’s Shiratani Unsuikyo, Japan: different mosses featured on the hike through forest there, but a very clear photo of P. commune, including its sporophytes and gametophytes; + bonus – a clear diagram illustrating the lifecycle of bryophytes

• Literary reference: ‘Gathering moss, A Natural and Cultural History of Mosses‘ by Robin Wall Kimmerer has a chapter titled ‘Binding up the wounds: mosses in ecological succession’, in which the author describes how Polytrichum somehow attached itself atop of thirty feet deep tailings and iron mine waste that created a Sahara in the middle of green Adirondacks. Little by little a carpet of Polytrichum mosses attracted and kept other seeds, and with help of rain and time a small grove of aspens now stands in this formerly desolate place. The trees brought birds and the birds brought berries…

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