Timmia Hedwig, 1801.

Timmia are acrocarpous and costate plants with stiff leaves somewhat reminiscent of members of the Polytrichaceae. Timmia is readily recognized by the sheathing base of every leaf. That leaf base is so radically different in color and orientation and is so closely wrapped around the stem that it may initially be misinterpreted as simply part of the stem.

Key to Timmia

The special character of leaf sheath differentiation allows Timmia to be confused only with Bartramia ithyphylla. That species of Bartramia and the three species of Timmia should be examined in the field by pulling a single leaf down and off the stem. Such a pulling action will remove the leaf exposing the sheathing base that completely surrounds the stem. This sheathing base is precisely defined in that the contraction to the leaf limb is so abrupt as to completely define the sheath as opposed to the leaf limb. Fully hydrated larger specimens of Timmia may be confused in the field with a Polytrichaceae, but the photosynthetic lamellae of that family show as longitudinal lines of more intensively green-pigmented cells even under a hand-lens. Timmia, when dry, may resemble in the field such highly crispate, plane-margined mosses as Trichostomum. However, if a Timmia leaf is carefully folded between one's fingers so as to view under a hand-lens across the adaxial surface of the leaf, the large single mammillae of each leaf cell of Timmia will appear as a contrast to the multiple papillae of Trichostomum and its allies.

Species included in this key are all in Timmiaceae:
Timmia austriaca Hedwig
Timmia bavarica Hessl.
Timmia megapolitana Hedwig, not known from CA

A. Leaf sheath orange to brown, lacking stereids in cross-sectional view; cilia of endostome not appendiculate; plant dioicous .....Timmia austriaca
A. Leaf sheath hyaline to cream-colored, with stereids; cilia appendiculate; plant monoicous .....B

B. Distal portion of leaf sheath with papillose cells; median cells of the limb mostly more than 10 µm in diameter; cells with corner thickenings; basal membrane of endostome with apertures .....Timmia megapolitana not known from CA
B. Distal portion of leaf sheath smooth; median cells of the limb mostly less than 10 µm; cells without corner thickenings; basal membrane of endostome without apertures .....Timmia bavarica