Common Haircap Moss (Polytrichum commune)

Detailed information for an alpine or subalpine species recorded along Howker Ridge Trail. Use the back link to return to the catalog.

Short Description

Common Haircap Moss is one of our largest mosses, creating miniature "forests" of its own on the ground. It grows in dense carpets or patches, often on damp, slightly acidic soil in woodlands. Along Howker Ridge, you might find it in seeps or near brook edges, where its 4-8 inch tall mats of **stiff, dark-green stems** stand out against lower mosses. Looking down at it, the plant shows a star-like arrangement of leaves at the tips of the stems – giving rise to another name, Star Moss. In the growing season, haircap moss is a vibrant green, and its colonies can cover logs, moist banks, or the bases of tree trunks. One striking feature comes when it reproduces: thin reddish stalks (setae) shoot up above the moss bed, each holding a brown spore capsule that is cylindric with a **tiny hairy cap (calyptra) on top** – hence “haircap.” These spore capsules, often appearing in late spring or summer, make the moss look like it’s dotted with a tiny upright matchsticks with fuzzy tips. The combination of height and distinctive reproductive structures makes haircap easy to identify. The underlayer of the moss clump consists of older, brown stems and a network of wiry rhizoids anchoring the colony. Haircap moss often colonizes bare, disturbed ground in forests – for example, after logging or fire, it can be an early colonizer due to its spores blowing in and germinating on raw soil. Over time, as leaf litter accumulates, it provides a substrate for seedlings of shrubs and trees to take root. This moss has a somewhat lustrous sheen, and water droplets often bead on its leaves after rain. When the sun hits a dewy patch of haircap moss in the morning, it’s a subtle but beautiful sight – like a miniature field of green stars covered in sparkling beads.

TYPE

Moss

ELEVATION

0–3,500 ft

HABITAT

Moist woods, bog edges, and streambanks; also found in clearings with acidic, damp soil

BLOOM / SEASON

Non-flowering (moss; spore capsules on tall stalks, often in summer)

LEAF & STEM

A robust acrocarpous moss that forms vertical shoots in colonies. Each stem is typically 4–8 inches (10–20 cm) tall, making it one of the tallest mosses. The stems are unbranched and erect, with a thick covering of leaves along their length. Leaves are 6–12 mm long, narrow lanceolate with a sharp point, and arranged around the stem such that the top of each stem has a star-like rosette of spreading leaves (visible when moist). These leaves are somewhat rigid and have a glossy deep green color; they are toothed along the margins and have a distinctive midrib. When dry, the leaves clasp tight to the stem, and the moss appears brownish-green and shriveled; when rehydrated, the leaves spread outward again. Haircap moss is dioicous, meaning it has separate male and female shoots. Male shoots often have a “splash cup” of modified leaves at their tip that hold sperm – these may appear as tiny flower-like rosettes. Female shoots, after fertilization, produce **sporophytes**: a long reddish stalk (seta) up to 15 cm tall that holds a spore capsule. The capsule is elongated and angular (like a tiny pepper shaker) and is covered by a hairy cap (the calyptra) when young – this hairy cap looks like a little pointed hood. Eventually, the cap falls off, revealing a lid (operculum) and a ring of “teeth” that release spores. The spores are microscopic, wind-dispersed. Beneath the moss, the stems have multicellular rhizoids that anchor them to soil. Large colonies feel a bit like a coarse, upright turf and can have considerable thickness (the bottom part of stems die and turn to peat while new growth continues on top).

SIMILAR SPECIES

Other **Polytrichum** species and large mosses resemble Common Haircap. **Polytrichum juniperinum (Juniper Haircap)** is smaller (2–4 inches) and often has a reddish stem tip and only one or few sporophytes per clump; its capsules are also more cylindrical and smaller. **Polytrichastrum (Polytrichum) ohioense** is another haircap moss found on logs, but tends to form smaller cushions and the capsules have different shapes. To the casual eye, haircap moss might be mistaken for tufts of grass or seedlings when not examined closely, due to its height and erect habit. However, grasses have jointed stems and roots and won’t have the distinctive star-like leaf arrangement. Some liverworts (e.g., Bazzania) can form mats in similar habitats, but those are creeping and much shorter. When sporophytes are present, haircap moss is unmistakable – no other common forest moss produces such tall stalks with hairy-capped capsules en masse. Also, if you pour water on a patch of haircap, the leaves spring open like a star – a quick way to differentiate it from other mosses that don’t have such large movement.

ECOLOGY

Haircap Moss often acts as a pioneer species on disturbed soil in woodlands and bog edges. Its spores can colonize bare acidic soil quickly, and the emerging moss mats then facilitate succession by collecting moisture and organic debris. This moss provides cover and moist microhabitat for many tiny creatures: springtails and other micro-arthropods are known to live within moss carpets, and salamanders or frogs in damp forests may use moss beds as hiding spots. Birds sometimes gather bits of moss (including haircap) to line their nests, taking advantage of its absorptive and insulating properties. Haircap Moss carpets are adept at retaining moisture – during rainfall, they soak up water like a sponge and then slowly release it, which helps maintain humidity at ground level and can reduce runoff. This contributes to the forest’s resilience in dry spells, as the moss will relinquish water to the environment as it dries. In nutrient-poor settings, haircap moss can also trap windblown particles and dust, incrementally improving soil fertility. The species is relatively tolerant of sun compared to many mosses, so it can survive in more open conditions until shaded competitors (like grasses or shrubs) overgrow it. It does prefer at least some shade and moisture – in fully sunny, dry sites it will not thrive. Interestingly, haircap moss and other Polytrichum have specialized internal tissue that conducts water (analogous to primitive vascular tissue), allowing them to grow taller than most mosses. Ecologically, this means haircap moss can outcompete shorter mosses for light in its niche. It’s one of the first mosses to colonize after fire in boreal regions, and helps stabilize the soil post-fire. In the White Mountains, you often see it at the edges of mountain bogs or wet ditches, where it forms a transition zone between aquatic sphagnum mats and the drier forest floor. Because it’s more tolerant of acidity, it often partners with blueberry bushes, rhododendrons, and other acid-loving plants in the understory. All told, haircap moss contributes significantly to water regulation, soil formation, and providing habitat complexity on the forest floor.

STATUS

Globally and regionally, Common Haircap Moss is thriving. It’s found on every continent except Antarctica and is one of the most **widely distributed mosses** (hence “common” in its name). In New Hampshire, it is frequently encountered and not under any threat. It’s not a species of concern in any conservation list. In some localized scenarios, pollution (like acid rain) might have historically impacted moss growth, but haircap moss tends to handle acidic precipitation fine (it actually lives in naturally acidic settings). Heavy logging or development can temporarily remove it from a site, but it often re-establishes as soon as conditions allow – sometimes being even among the first to carpet a skid trail or stump dump after logging, helping recovery. Climate warming could alter its habitat a bit: if boreal bogs shrink, haircap mats at their edges might too, but conversely more frequent disturbances could give it new colonization opportunities. The species has even been used as an indicator of habitat quality; its presence suggests a relatively intact, moist forest floor. No harvesting pressure exists (though historically, dried haircap moss has been used as stuffing for bedding or insulation in some cultures, this is negligible now). In summary, haircap moss remains abundant from the lowest valleys to near alpine zones of the White Mountains. As long as forests remain, this resilient moss will continue to flourish. Efforts to maintain water quality and minimize pollution will only further ensure its well-being, but currently it shows no signs of decline.

Field Notes

A robust acrocarpous moss that forms vertical shoots in colonies. Each stem is typically 4–8 inches (10–20 cm) tall, making it one of the tallest mosses. The stems are unbranched and erect, with a thick covering of leaves along their length. Leaves are 6–12 mm long, narrow lanceolate with a sharp point, and arranged around the stem such that the top of each stem has a star-like rosette of spreading leaves (visible when moist). These leaves are somewhat rigid and have a glossy deep green color; they are toothed along the margins and have a distinctive midrib. When dry, the leaves clasp tight to the stem, and the moss appears brownish-green and shriveled; when rehydrated, the leaves spread outward again. Haircap moss is dioicous, meaning it has separate male and female shoots. Male shoots often have a “splash cup” of modified leaves at their tip that hold sperm – these may appear as tiny flower-like rosettes. Female shoots, after fertilization, produce **sporophytes**: a long reddish stalk (seta) up to 15 cm tall that holds a spore capsule. The capsule is elongated and angular (like a tiny pepper shaker) and is covered by a hairy cap (the calyptra) when young – this hairy cap looks like a little pointed hood. Eventually, the cap falls off, revealing a lid (operculum) and a ring of “teeth” that release spores. The spores are microscopic, wind-dispersed. Beneath the moss, the stems have multicellular rhizoids that anchor them to soil. Large colonies feel a bit like a coarse, upright turf and can have considerable thickness (the bottom part of stems die and turn to peat while new growth continues on top).
Haircap Moss often acts as a pioneer species on disturbed soil in woodlands and bog edges. Its spores can colonize bare acidic soil quickly, and the emerging moss mats then facilitate succession by collecting moisture and organic debris. This moss provides cover and moist microhabitat for many tiny creatures: springtails and other micro-arthropods are known to live within moss carpets, and salamanders or frogs in damp forests may use moss beds as hiding spots. Birds sometimes gather bits of moss (including haircap) to line their nests, taking advantage of its absorptive and insulating properties. Haircap Moss carpets are adept at retaining moisture – during rainfall, they soak up water like a sponge and then slowly release it, which helps maintain humidity at ground level and can reduce runoff. This contributes to the forest’s resilience in dry spells, as the moss will relinquish water to the environment as it dries. In nutrient-poor settings, haircap moss can also trap windblown particles and dust, incrementally improving soil fertility. The species is relatively tolerant of sun compared to many mosses, so it can survive in more open conditions until shaded competitors (like grasses or shrubs) overgrow it. It does prefer at least some shade and moisture – in fully sunny, dry sites it will not thrive. Interestingly, haircap moss and other Polytrichum have specialized internal tissue that conducts water (analogous to primitive vascular tissue), allowing them to grow taller than most mosses. Ecologically, this means haircap moss can outcompete shorter mosses for light in its niche. It’s one of the first mosses to colonize after fire in boreal regions, and helps stabilize the soil post-fire. In the White Mountains, you often see it at the edges of mountain bogs or wet ditches, where it forms a transition zone between aquatic sphagnum mats and the drier forest floor. Because it’s more tolerant of acidity, it often partners with blueberry bushes, rhododendrons, and other acid-loving plants in the understory. All told, haircap moss contributes significantly to water regulation, soil formation, and providing habitat complexity on the forest floor.
Globally and regionally, Common Haircap Moss is thriving. It’s found on every continent except Antarctica and is one of the most **widely distributed mosses** (hence “common” in its name). In New Hampshire, it is frequently encountered and not under any threat. It’s not a species of concern in any conservation list. In some localized scenarios, pollution (like acid rain) might have historically impacted moss growth, but haircap moss tends to handle acidic precipitation fine (it actually lives in naturally acidic settings). Heavy logging or development can temporarily remove it from a site, but it often re-establishes as soon as conditions allow – sometimes being even among the first to carpet a skid trail or stump dump after logging, helping recovery. Climate warming could alter its habitat a bit: if boreal bogs shrink, haircap mats at their edges might too, but conversely more frequent disturbances could give it new colonization opportunities. The species has even been used as an indicator of habitat quality; its presence suggests a relatively intact, moist forest floor. No harvesting pressure exists (though historically, dried haircap moss has been used as stuffing for bedding or insulation in some cultures, this is negligible now). In summary, haircap moss remains abundant from the lowest valleys to near alpine zones of the White Mountains. As long as forests remain, this resilient moss will continue to flourish. Efforts to maintain water quality and minimize pollution will only further ensure its well-being, but currently it shows no signs of decline.

Howker Ridge • Plant