Slender Starburst Moss, Atrichum angustatum
Polytrichaceae or Haircap Moss Family
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A robust moss up to an inch tall. Often some plants will often have
spore capsules on long stalks arising from the top, about doubling the
plant height. When moist, the leaves spread widely and present a
starburst look from the top. When dry, the leaves twist and contort and
make the plant look dead. Wet plants are shown in the lefthand pictures
at right and below. Dry plants can be seen in the righthand pictures,
and also in the habitat shot at left.
The leaves are long, narrow, and strongly toothed. There is a very
strong costa (midvein) down the centerline of each leaf. Close
inspection with a good handlens will show longitudinal striations. The
spore capsule is reddish brown. When young and fresh there is a little
cap on top; the cap is lost when the spores mature, revealing a ring of
teeth around the opening. Capsules persist long after the spores are
dispersed. Mosses in general have never evolved the control mechanisms to grow multicellular leaves, so their leaves are only one cell thick. A single cell is inefficient at absorbing light for photosynthesis. Members of the Polytrichaceae have evolved one solution. They grow little walls, one cell thick, running alongside the costa. These walls can capture more light for photosynthesis. A cross-section through the leaf, examined under the microscope (bottom right picture, at 100x magnification) shows there are 6-9 such walls, each 5-10 cells tall. The bottom left picture shows the upper part of a leaf at 35x, and the bottom middle shows the teeth and the individual leaf cells at 430x. This species has the smallest cells of any species in the genus, about 16 micrometers (a micrometer is a thousandth of a milimeter). |
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The hair cap mosses are named for the hairs on the cap of the spore case. The genus that gave the family it's name means "many (Poly-) hairs (trichum)." The genus name Atrichum means "no hairs," and fittingly members of this genus are bald. Slender Starburst is a common moss along roadsides and trails in the woods, eastern North America from Newfoundland to Manitoba, south to Texas and Florida, and also in Central America, the Carribean and western Europe. In Wildwood look for it along the trails, especially on the western slope. All hair cap mosses look roughly similar. This species is fairly easy to identify because of the extreme crisping and contortions of the dried leaves. |
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