Friday, August 30, 2013

Mosses of Central Florida 4. Isopterygium tenerum

The asymmetrical capsules of Isopterygium rise on
long stalks from along the creeping stems, and curve to the side.
[For other mosses in this series, see the Table of Contents]

Isopterygium tenerum (Sw.) Mitt. is one of the most common mosses in Central Florida, yet easily confused with others of similar growth habit.  That habit is what we might call "creeping." as apposed to the upright habit of the three previous mosses in this series. Stems lie against the ground or flop over each other in a thick mat.  The numerous delicate leaves spread out, largely on the two sides of the stem so as to face upward and gather the maximum amount of light.  The leaves remain in that spread out condition when they dry.  They  lack a midrib and the cells are uniformly narrow and worm-like, with thick walls.  The sporophytes emerge from along the stem, lifting the sporangia, or capsules, high above the mat of vegetation.  The sporangia are asymmetrical and curve to the side.  When dry, the capsules are constricted below the mouth, which is lined with two rows of teeth.

The opening of the capsule is
surrounded by two rows of teeth, the
outer short, curved and stiff, and the
inner longer, thinner and straight.
These teeth change shape with changes
in humidity, and help to loosen and
eject the spores. This double row of
conspicuous teeth is characteristic
of the Hypnaceae and related
Isopterygium is found throughout Florida, commonly  at the bases of trees: on the lower trunk, roots, and surrounding wet soil.
The leaf cells of Isopterygium and its relatives are narrow and worm-like, with thick, clear walls.
The leaves are simple in structure, lacking a midrib (costa) or specialized cells at the base.

The delicate, feathery foliage of Isopterygium spreads out into a tangled mat.
The flat leaves  maintain their shape and orientation as they dry.
Similar common species include Sematophyllum adnatum and Entodon seductrix.  The Sematophyllum differs most conspicuously when it is dry, as the stems and the leaves curve toward the side. In Entodon, however, the leaves press against the stem when dry, making the shoots resemble little twigs of juniper. Their sporangia are also symmetrical and upright.  The less common Taxithelium planum is similar, but the leaves are covered with many small bumps, or papillae. Schwetskiopsis fabrona, also less common, is
similar, but has papillae at the upper end of each leaf cell, and the leaves are pressed to the stem when dry, like Entodon.