Specimen #7: Polytrichum commune

Collection #: 7

Scientific Name: Polytrichum commune

Phylum: Bryophyta; Polytrichopsida

Order: Polytrichales

Family: Polytrichaceae

Common Name: common haircap moss

Location: the Triangle Lake area

Habitat: On soil before get onto the boardwalk

Date of collecting: September 10th

Collector: Cornelia

Notes: looks a little bit woody; each individual grows separately

How did I key this out:

Fig.1 Group picture                                                                        Fig.2 Single plant with measurement

Fig.3a Single leaf under a dissecting scope

Fig.3b Single leaf under a dissecting scope

From the picture of the group of the plant sample (Fig.1) and individual plants (Fig.2), we could easily figure that this plant is in the acrocarp growth form. The leaf picture (Fig.3a and Fig.3b) shows that this specimen is with lance-shaped leaves (I thought it was hairlike at the beginning; but it's actually lance since it's wider and the midrib is somehow visible) with a midrib (pay special attention by the bottom of the leaf). By knowing these features, we could now go to the key: KEY II: Acrocarps with Lance-shaped Leaves.

The following steps is how I went through the keys:
1. (B) Plants darker green, yellow green, or brownish black, shoots loosely associated or if densely packed then not in domed mounds; leaves flat or folded but not tubular, with midrib usually visible at least at base of leaf. (See Fig.1 and Fig.2 for this fact.) (3)
3. (B) Plants on soil, rocks, trees, or logs in dry areas, or if in wetter areas, not submerged in water; leaves not folded at base. (4)
4. (B) Leaf surface not rippled or wavy when wet. (See Fig.3a and Fig.3b for this fact.) (9)

9. (A) Leaves mostly ≥4 mm long (some at base or tip of stem may be shorter). (10)

10. (B) Wet leaves stiff, thick, and opaque when held up to light (reminiscent of conifer needles); midrib difficult to see except at leaf base. (See Fig.3a and Fig.3b for this fact.) (14)

14. (B) Leaf margin toothed except along clasping leaf base (See Fig.3a and Fig.3b for this fact); capsules with or without disk. (17)

17. (B) Capsules 4-sided like a box. (19)

19. (A) Capsule with a disk at attachment to stalk. (Polytrichum commune, P57)

Fig.4 Cell structure

Description of the species:

Appearance: Large, 5-15 cm tall, upright dark green or brownish plants that superficially look like pine tree seedlings growing in thick patches. Narrow pointed leaves are held upright and pressed to stem with recurved tips when dry; when wet, they spread outward 90 degrees. Male pants are topped by splash cups, cupped rosettes of short leaves surrounding the sex organs.

Leaves: Narrow, lance-shaped from clasping square base, 6-10 mm long. Leaves are thick, opaque, and flat, especially when wet, but never with deeply inrolled edges and although sharp-tipped, without long needle tips. Midrib is brownish, opaque, and runs to top, most visible in pale clasping leaf base; otherwise it fills leaf blade and is hard to recognize. Teeth run from tip to clasping leaf base.

Capsule: Four-sided, short-rectangular to cubic, like a box, with a disk at the base. Capsules are upright initially, inclined with age; covered in a very hairy hood while developing in the summer. Stalk is 5-9 cm tall.

Habitat: Moist soil, often shaded, in fields or woodlands. Also along margins of bogs, swamps, and lakes.

Microscopic Features: Cross-section of leaf shows thin strips of cells, 1-cell wide and 4-9 high, along the midrib; the uppermost cell in each stack is wide and notched.

Collecting and keying story:

This was the first specimen I sampled at the Triangle Lake area. They grew together with some fake mosses so when I first keyed it wrong I thought I got the fake ones… But it turns out to be alright when I changed the “hairlike leaf” clue into “lance-shaped leaf”.

To key out this specimen, a sample of the capsule was really necessary since the last 3 keys were all about the capsule. But unfortunately, I didn’t have one. So what Willa helped me to do, was to “assume” what the capsule would look like, and surprisingly it worked. Later on after I keyed this, I found that my classmate Breanna has had collected a sample of the same plant, and she had the capsule. I double checked with her, and now I’m really confident that I keyed this thing right.

Phylum, order and family name cited from:
https://en.wikipedia.org/wiki/Polytrichum_commune

Keys cited from:

  Common Mosses of the Northeast and Appalachians by Karl B. McKnight, Joseph R. Rohrer, Kirsten McKnight Ward and Warren J. Perdrizet. This book is in the series of the Princeton Field Guides and was published by Princeton University Press with copyright @ 2013.