Montana Field Guide

Plants: Acrocarpous. Growing in upright clumps or cushions (Lawton 1971), green to very dark green. Stems sometimes reaching 20 mm in height; possessing a central strand; hairs of the leaf axil ca 5 cells long, the first 1 or 2 cells brown (FNA 2007).

Leaves: Overlapping, upright and close to the stem to spreading slightly when dry, sometimes spreading more than 45 degrees, 0.8-3 mm in length, grooved transversely or sometimes along the costa, strap-shaped or lance-shaped with ovate tendencies, narrowing to the acute or sometimes subulate leaf tip, the leaf tip sometimes easily broken; margins curved back and downward and centered at mid-leaf for ca 1/2 the leaf length; costa extending to or shortly beyond the leaf tip, typically as a wide and dull-ended subula (FNA 2007).

Leaf Cells: Upper laminal cells isodiametric, smooth or with simple or 2-lobed papillae, the upper margins or apex sometimes almost entirely of 2 cell-layers; proximal laminal cells quadrangular; costa with square ventral cells, in X-section with 1 row of guide cells (FNA 2007), and frequently with ventral and dorsal stereid bands, the ventral band weak (Lawton 1971).

Didymodon rigidulus var. ditrichoides: Leaves upright and strongly flattened to the stem when dry, narrowly lance-shaped; costa extending well beyond the leaf tip; upper lamina 1 cell-layer thick.

Didymodon rigidulus var. gracilis: Present in Montana. Leaves upright and near to the stem or spreading a little when dry; costa typically extending to the leaf tip or shortly beyond it, forming a stiff subula; upper margins sometimes 2 cell-layers thick in places.

Didymodon rigidulus var. icmadophilus: Leaves upright and near to the stem or spreading a little when dry; costa typically extending well beyond the apex, the subula easily broken; upper lamina seldom patchily 2 cell-layers thick.

Didymodon rigidulus var. rigidulus: Leaves upright and near to the stem or spreading a little when dry, spreading when wet, lance-shaped with oblong tendencies or long and deltoid; costa typically extending beyond the stem shortly with a dull end; upper lamina 2 cell-layers thick at the leaf tip or along the edges.

Didymodon rigidulus var. subulatus: Leaves upright and near to the stem or spreading a little when dry, lance-shaped, somewhat uniform in width; costa extending beyond the stem, forming a subula; lamina 2 cell-layers thick from mid-leaf to ca 3/4 up the leaf.

Adapted from FNA 2007.

Didymodon rigidulus var. gracilis: Fruit ripens nearly throughout the year.

Didymodon rigidulus var. icmadophilus: Fruit ripens summer through autumn.

Didymodon rigidulus var. rigidulus: Fruit ripens mid-spring through early autumn.

Didymodon rigidulus var. subulatus: Time of fruit ripening unknown.

Adapted from FNA 2007.

Varieties gracilis and icmadophilus resemble each other generally; variety icmadophilus has longer, almost thread-like subulae, and its upper cells are mostly smooth rather than usually papillose as in variety gracilis.

Adapted from FNA 2007.

Didymodon rigidulus var. ditrichoides: Calcareous crags, beyond timberline. Elevation: 3940 feet.

Didymodon rigidulus var. gracilis: Calcareous crags and shelves, soil, areas of small rock fragments basalt, trail edges, tundra. Elevation: 0-9840 feet.

Didymodon rigidulus var. icmadophilus: Calcareous stones, sandstone, soil. Elevation: 130-9190 feet.

Didymodon rigidulus var. rigidulus: Calcareous stones, crags, bluffs, tufa. Elevation: 200-1640 feet.

Didymodon rigidulus var. subulatus: Soil, stones, shelves, gorges. Elevation: 3280-6560 feet.

Adapted from FNA 2007.

Dioicous. Perichaetia occurring at the stem apices. Seta sometimes reaching 17 mm in height. Capsule up to 2 mm in length; peristome with 32 teeth or 16 teeth divided to the base, sometimes small or lacking, thread-like to deltoid, sometimes scarcely spiraled.

Specialized vegetative reproduction by several-celled gemmae produced in the leaf axils.

Didymodon rigidulus var. ditrichoides: Peristome unknown; gemmae wanting.

Didymodon rigidulus var. gracilis: Peristome teeth short or longer and spiraled; gemmae frequently produced in axils of upper leaves.

Didymodon rigidulus var. icmadophilus: Peristome teeth short or longer and spiraled; gemmae rare.

Didymodon rigidulus var. rigidulus: Peristome teeth short or longer and spiraled; gemmae frequently produced.

Didymodon rigidulus var. subulatus: Peristome with 16 short or not fully developed teeth.

Adapted from FNA 2007.