Thuidiaceae

Growth Form and Habit

Plants are pleurocarpous, typically medium to large, forming intricate, interwoven mats or loose wefts. The branching pattern is highly characteristic: stems are usually creeping or arching and give rise to branches in a regularly 1-, 2-, or 3-pinnate fashion, creating a flat, layered, fern-like appearance. The overall texture can be somewhat stiff.

Stems and Paraphyllia

Stems and often primary branches are typically covered with paraphyllia. These are small, filamentous or leaf-like appendages found on the stem/branch surface between the leaves. The abundance and morphology (shape, branching) of paraphyllia vary among genera and are important taxonomic characters. They likely increase surface area for water retention or photosynthesis.

Leaves

Leaves are typically dimorphic (differing between stems and branches). Stem leaves are usually larger, broadly ovate or triangular-ovate, often abruptly narrowed to an acuminate (tapering) apex, frequently strongly plicate (with longitudinal folds or pleats), and sometimes with recurved margins. Branch leaves are smaller, generally ovate to lanceolate, concave, and less strongly plicate. Leaf margins are typically serrulate or crenulate, especially towards the apex. The costa (midrib) is single and usually strong, ending below the apex or occasionally percurrent. Leaf cells are typically small, isodiametric (quadrate, rounded, or hexagonal) to shortly rectangular, usually thick-walled, and characteristically papillose. Papillae are usually single and centered over the cell lumen, but variations exist. Alar cells are generally not strongly differentiated.

Sporophyte (Capsule)

Sporophytes arise laterally from the main stems. The seta (stalk) is long, slender to stout, usually smooth, and often reddish. The capsule is typically inclined to horizontal, usually curved (arcuate), and ovoid to cylindrical. The operculum (lid) is typically conical to rostrate (beaked).

The peristome is double and well-developed, of the Hypnoid type. The 16 outer exostome teeth are yellowish to brownish, lanceolate, typically cross-striate below and papillose above. The inner endostome consists of a high basal membrane, well-developed, keeled segments (often perforated along the keel), and usually robust, often nodose or appendiculate cilia (typically in groups of 1-3).

Habitat

Commonly found in mesic (moderately moist) forests and woodlands. They grow on a variety of substrates, including the forest floor (soil, humus, leaf litter), decaying logs and stumps, rock surfaces (often shaded), and the bases of trees. Some species can tolerate more open or disturbed habitats like lawns or pastures.