Thursday, October 19, 2017

Mosses of Central Florida 33. Rhynchostegium serrulatum

A spreading colony of Rhynchostegium serrulatum.  All
photos by Robert A.Klips, Ohio Moss and Lichen Association.
Rhynchostegium serrulatum (Hedwig) A. Jaeger (Brachytheciaceae) is a spreading, mat-forming
Leaves are notably toothed and the midrib peters out before
the tip. Cells are long and worm-like.
moss found on soil, rotting wood, and tree bases. Leafy stems grow indefinitely with numerous leaves spreading mostly to the two sides of the stem.  Spore capsules arise from along the stems, and are strongly curved.  Leaves are spiny along the margins, particularly toward the tip.  The midrib is relatively weak, generally not reaching the tip.  Leaf cells are elongate and curved, with thick walls, what I often refer to as worm-like.
Spore capsules are strongly arched, with
a swollen tip.

From it's bent spore capsules and spreading leafy stems, this species could be mistaken for the common Isopterygium tenerum. Even the elongate, worm-shaped leaf cells are similar.  But the most obvious difference is the presence of a midrib here, which is lacking in Isopterygium and the greater number of teeth along the leaf margin.  The capsules of Rhynchostegium are also more slender and more bent, almost into a U-shape, but with the tip enlarged and more cone-shaped.  Differences between the Brachystegiaceae and the Hypnaceae, to which Isopterygium belongs, are obscure and technical.

Rhynchostegium serrulatum is found throughout eastern North America, as far west as New Mexico, and north to Ontario and Quebec. In Florida, it appears to be distributed throughout the state.  Gaps in county records are more likely due to lack of collections than absence of the species.

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