Timmiaceae. Genus Timmia

1. Leaves detaching easily due to 1-3 rows of thin-walled cells across leaf bases; sheathing leaf base with orange upper cells and conspicuously pale basal cells; basal leaf cells equally thickened on dorsal and ventral sides; dioicous 2
Leaves not readily detaching; sheathing leaf base uniformly colored; basal leaf cells thicker on dorsal than on ventral side; autoicous or dioicous 4
2. Upper leaf cells papillose or papillose-mammillose on dorsal or both sides 3. T. sibirica

In Russia this species is rather strictly confined to the permafrost regions. It can be recognized by the presence of papillose leaf cells on dorsal, and occasionally ventral, leaf surfaces.

Upper leaf cells mammillose 3
3. Leaves 2-5 mm long, at midleaf 0.5-0.6 mm wide; median leaf cells 6-10 m wide 2. T. comata

This species occurs in more severe climatic areas than T. norvegica. It differs from T. norvegica by overlapping quantitative characters, but usually does not present identification problems.

Leaves 3-9 mm long, at midleaf 0.8-1. 1 mm wide; median leaf cells 10-20 m wide 1. T. norvegica

This species occurs sporadically in the high mountains of Western Caucasus and is known also from scattered localities throughout Russia, extending to the Arctic. It, along with T. comata and T. sibirica, differs from other species of the genus in having a row of thin-walled, pellucid cells at the leaf/stem junction that make the leaves easily detachable.

4(1). Sheathing leaf base orange; basal cells 7-10 m wide, more or less porose; basal leaf margins distinctly bordered by narrow cells with strongly oblique walls; dioicous, rarely producing sporophytes; mostly northern species 6. T. austriaca

Arctic-alpine species occuring sporadically in the northern taiga zone in European Russia and rather rare in other regions. In mountain areas it occurs mostly at middle elevations.

Sheathing leaf base light-yellowish or rarely slightly orange; basal cells 10-15 m wide, not or indistinctly porose; leaf margins inconspicuously bordered by slightly narrowed cells, without strongly oblique walls; monoicous, sporadically producing sporophytes; widespread species 5
5. Laminal cells square to polygonal, 6-9 m wide; leaf limb margins strongly serrate above and serrulate to almost entire near sheathing bases; upper sheath cells on dorsal side smooth 5. T. bavarica

The differences between T. bavarica and T. megapolitana are mainly quantitative, but their distribution in Russia is different. The former is mostly a mountain species, often growing above tree-line, whereas T. megapolitana is mostly a lowland species, nearly absent in mountain regions and reaching only lower elevations.

Laminal cells polygonal, 10-14(-16) m wide; leaf limb margins rather evenly serrate; upper sheath cells on dorsal side papillose 4. T. megapolitana

This species is rather common in the central parts of European Russia and also occurs in southern areas of Asian Russia. It grows on wet, shady limestone outcrops and on alluvium on steep creek banks, occasionally also on tree bases along river banks.