Mnium hornum Hedw.
Swan’s-neck thyme-moss, horn calcareous moss
Swan’s neck moss is native to Europe and North America. The ‘M’ in the genus name, Mnium, is silent.
Identification: The stems of this moss are ¾–1½″ (2–4 cm) tall, with toothed leaves ⅛–¼″ (4–8 mm) long. Leaves have obvious midribs that end prior to the leaf tips. Spore-containing capsules are about ⅛″ long ⨉ 1/32″ around (5 ⨉ 0.8 mm) long. They are nodding, atop seta ⅞–1¾″ (2.5–5 cm) long, hence the name swan’s neck moss.
Habitats: Damp woodland conditions, especially in acidic soil, such as oak-birch, beech and pine woodlands. It takes up residence on the ground, rocks, logs, roots, and tree bases.
Online References:
6/19/2017 · Willard Brook State Park, Ashby, Massachusetts · ≈ 7 × 4½″ (18 × 12 cm) 
7/5/2025 · Cathance River Nature Preserve, Topsham, Maine · ≈ 9 × 6″ (21 × 14 cm) 
7/7/2026 · Butler Head Preserve, Bath, Maine · ≈ 6 × 3½″ (14 × 9.6 cm) 
6/13/2021 · Cathance River Nature Preserve, Topsham, Maine · ≈ 6 × 4″ (16 × 10 cm) 
6/13/2021 · Cathance River Nature Preserve, Topsham, Maine · ≈ 7 × 4½″ (17 × 11 cm) 
6/9/2016 · Monhegan Island, Maine 
9/16/2016 · Sieur de Monts Botanical Gardens, Acadia National Park, Bar Harbor, Maine 
9/16/2016 · Sieur de Monts Botanical Gardens, Acadia National Park, Bar Harbor, Maine 
7/5/2025 · Cathance River Nature Preserve, Topsham, Maine · ≈ 8 × 5″ (19 × 12 cm) 
4/24/2016 · Blue Trail, Willard Brook State Park, Ashby, New Hampshire 
7/1/2026 · Widgeon Cove, Harpswell, Maine · ≈ 7 × 4½″ (17 × 11 cm) 
6/9/2016 · Monhegan Island, Maine 
6/9/2016 · Monhegan Island, Maine 
4/24/2016 · Blue Trail, Willard Brook State Park, Ashby, New Hampshire 
| Kingdom | Plantae | Plants, but not fungi, lichens, or algae (from Stearn's Botanical Latin) |
| Division | Bryophyta | Mosses |
| Subdivision | Musci | Mosses (all 12,000 of them) |
| Class | Bryopsida | Mosses with arthrodontous spore capsules, which is most of them |
| Subclass | Bryidae | Mosses with a double peristome with alternating tooth segments |
| Order | Bryales | Acrocarpous mosses containing about 500 species world-wide, and found growing on soil, rocks and walls |
| Family | Mniaceae | Acrocarpous mosses, typically forming tufts or sods in moist, shaded habitats like forest floors, stream banks, logs, and rocks |
| Genus | Mnium | Calcerous and allied mosses |
| Species | hornum | Hornlike |
Mnium hornum description by Thomas H. Kent, not updated.
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