Bartramiaceae. Genus Philonotis

1. Leaf cells with central papillae 11.P. yezoana

Philonotis yezoana is distinguished by its slender habit and the upper leaf cells with a central papilla. Although some species of the genus may have single cells with central papillae, the majority of their cells have the mammillae/papillae at proximal or distal ends of the cells. The species is known in Russia only in the Far East, where it is rather rare in Kamchatka, Kuril Islands, Sakhalin and Primorsky Territory.

— Leaf cells with mammillae/papillae on either lower or upper cell ends, occasionally with central papillae in some cells 2

2. Upper leaf cells with mammillae/papillae at lower cell ends; lower leaf border with double-crenulate teeth (i.e., two adjoining cells form a tooth) 3

— Upper leaf cells with mammillae/papillae at upper cell ends; lower leaf border entire, serrate or serrulate 10

3. Leaves ranked in five distinct spiral rows 4

— Leaves not ranked in distinct rows 5

4. Leaves falcate, secund, ovate, gradually acute; costae usually coarsely mammillose at back ± throughout 9.P. seriata

The five ranked leaves in Philonotis seriata are best seen on fresh specimens in the field. Its bulging costae are much stronger than those of P. fontana and they have large colourless mammillae on the dorsal surface (best seen in side view). The costae of related species have only small papillae or scindulae. Philonotis seriata is known from a few mountain (Urals, Altai, West Sayans, Khibiny) and lowland (Yamal, valley of Yenissey) localities. It grows in spring mires and spring-fed brooks in areas with siliceous bedrock.

— Leaves spirally twisted, from broadly ovate base abruptly acuminate; costae rarely coarsely mammillose 8.P. americana

Plants of Philonotis americana have a distinctive aspect due to their twisted, non-imbricate leaves, and as a result its brownish stems are visible between the leaves. The wet leaves of P. americana differ from the wet leaves of P. seriata in being straight or slightly secund rather than falcate. This species has only recently been found in Asia: Kamchatka, Kuril Islands, Sakhalin, and Japan.

5. Leaf cells pellucid, smooth or low-mammillose; leaf margins plain or revolute; upper leaf cells as wide as lower leaf cells or somewhat narrower 6

— Leaf cells opaque or only basal leaf cells ± pellucid, distinctly mammillose/papillose; leaf margins recurved or revolute; upper leaf cells clearly narrower (–1/3) than lower leaf cells 7

6. Leaves erect, plicate or smooth, triangular, ovate or broadly ovate; leaf apices shortly acute or obtuse; leaf margins plain or recurved; costae strong; leaf cells quadrate, rectangular or rhomboidal, usually thin-walled; apical cells narrowly elongate or vermicular, thick-walled; inner perigonial leaves short acute or obtuse 6.P. fontana, male plants

— Leaves usually secund, smooth, ovate; leaf apices acute, leaf margins plane or narrowly recurved; costae narrow; leaf cells rectangular or rhomboidal, cells at apiculus + rectangular, all leaf cells + thin-walled; inner perigonial leaves acuminate 5.P. caespitosa

Dried specimens of Philonotis caespitosa remain pale-green, while specimens of the other species of section Philonotis turn yellowish to brownish when dried. Important microscopic characters of P. caespitosa include weakly serrate leaf margins; non-plicate leaves; and lax leaf areolation. The leaves of P. caespitosa are much more translucent than those of related species with linear or vermicular apical cells. When identifying collections of P. fontana and P. caespitosa only fully grown, old stems from the previous growing season should be used. Philonotis fontana differs from P. caespitosa in having broadly ovate, erect leaf bases ± ab­ruptly narrowed to slender acumina, strongly recurved leaf margins and plicate leaves. In contrast P. caepitosa has ovate, spreading to flexuose leaves, gradually tapered acumina, plane or narrowly recurved leaf margins, and smooth leaves. In Russia, P. caespitosa has been confirmed only from its European regions.

7. Stem tips with spiraling leaves; leaves twisted when dry, diverging from stems at wide angles 8.P. americana

— Stem tips with straight or falcate-secund; leaves straight when dry, erect or spreading at base 8

8. Plants robust; leaves (1.5–)1.8–3.0 mm long; costae 60–125(–200) µm wide near base; juxtacostal cells at widest part of leaf mostly 48–100 µm long, narrowly rectangular, thin-walled, pellucid; perigonial leaves acute 10.P. calcarea

Philonotis calcarea has large, rather stiff plants with narrowly elongate basal leaf cells. The species occurs sporadically in Europaean Russia from the northern regions to the Caucasus, as well as isolated localities in the Altai.

— Plants tiny to moderately robust; leaves (0.5–) 1–2 mm long; costae 25–80 µm wide near base; juxtacostal cells at widest part of leaf 24–40 µm long, quadrate, rectangular or rhomboidal, thin- to firm-walled, pellucid or opaque; perigonial leaves obtuse or acute 9

9. Stems compactly tufted; leaves tapering from ovate bases to acuminate or cuspidate, straight or slightly flexuose apices; leaf acumina bending in different directions; costae excurrent to long-excurrent; basal leaf cells opaque, firm-walled ± rectangular; inner perigonial leaves acute 7.P. tomentella

Philonotis tomentella is a more northern species than P. fontana, where it replaces P. fontana in permafrost regions. However, the two species sometimes occur together in montane regions, although P. tomentella usually occurs at higher elevations than P. fontana.

— Stems loosely tufted; leaves tapering from broadly ovate bases to acute or acuminate apices, leaf acumina one-sidedly secund (especially at stem apices); costae percurrent or scarcely excurrent (rarely long-excurrent); basal leaf cells ± pellucid, thin-walled, quadrate, rectangular or rhomboidal; inner perigonial leaves obtuse to short-acute 6.P. fontana

There are many key differences between Philo­notis fontana and P. tomentella. Nevertheless separating these two species is not easy because many collections have imperfectly developed plants that are difficult to evaluate. The presence of obtuse inner perigonial leaves in P. fontana has been used to separate it from P. tomentella which has acute to acuminate inner perigonial leaves. Even though this difference has been emphasized in many floras, a more reliable distinction between the two species seems to be stem leaf form below the perigonia. In P. fontana these leaves are often straight and have short acute or obtuse apices, contrary to secund leaves with longer acumina on female and sterile shoots. In contrast, these leaves in P. tomentella do not differ as much from the vegetative leaves on female and sterile shoots. Overall, P. fontana is the most common species of the genus in Russia, however in the Arctic zone it is nearly absent.

10(2). Autoicous with bud-like perigonia below perichaetia; costae strong, excurrent 3. P. rigida

Known in Russia from a single collection in the Black Sea coastal area of the Caucasus. It is strikingly different from all other species of the genus in having rigid plants; narrow leaves; strongly excurrent costae; and an autoicous sexual condition. Russian (and Georgian) plants of P. rigida differ from West European in longer leaves, 2.0–2.8 vs. 1.0–1.6(–2.0) mm, thus further study on their identity is needed.

— Dioicous; costae slender, percurrent to short excurrent 11

11. Plants tiny, 0.5–2.0 cm tall, thread-like; stems upright or procumbent; leaves straight, linear-lanceolate, slightly concave, not in rows; leaf cells mammillose/papillose at upper cell ends or bulging at lower cell ends at leaf base and mammillose/papillose in upper cells end at leaf apices 4. P. capillaris

Philonots capillaris can be characterized by its: very slender thread-like aspect; lax, pellucid, thin-walled leaf cells; low mammillae/papillae at the upper cell ends; and upper/lower leaf cells that are ± the same width. It closely resembles P. caespitosa, but that species has mammillae at the lower cell ends, while in P. capillaris the leaf cells have papillae at the upper ends or bulging at the lower ends only at the base of the leaves. Further studies may reveal that P. capillaris, as circumscribed here, includes other cryptic species. Philonots capillaris is rare in Russia, known only from a few collections in the Caucasus, Yakutia, Commander Islands, and Amurskaya Province.

— Plants medium-sized, 1–5(–9) cm tall, not thread-like; stems upright; leaves falcate-secund, ovate-lanceolate or triangular-lanceolate; gradually tapered to acute or acuminate apices, concave or keeled, often distinctly in five rows, leaf cells mammillose/papillose at upper cell ends 12

12. Leaves widely spaced, slightly keeled to concave; marginal teeth single; costae 50–75 µm wide at base; brood branch stalks long, leaflets acuminate 2. P. marchica

The leaves of Philonotis marchica are more weakly keeled than those of P. falcata, have narrower costae, and consistently single marginal teeth. In addition, the basal leaf cell papillae appear to be higher than those of P. falcata and the cells are narrower. As a result the basal leaf cells are more opaque than the pellucid basal leaf cells of P. falcata. Most collections of P. marchica are from European Russia. The species is also known from a few localities in the Caucasus and Kuril Islands.

— Leaves imbricate, strongly carinate; marginal teeth single and/or double; costae 75–100 µm wide at base; brood branch stalks short, leaflets acute 1. P. falcata

The best diagnostic features ofP. falcata are its strongly carinate leaves that are often clearly arranged in rows, and leaf cells with mammillae/papillae at the upper ends. At times the leaves are somewhat distantly spaced and this obscures their arrangement in the rows. But these plants typically have innovations with clearly ranked, immature leaves (best seen when wet). Philonotis falcata is often misidentified as P. seriata, another species with leaves in five rows. Philo­notis seriata is distinguished from P. falcata by the presence of mammillae/papillae at the lower ends of the leaf cells. Philonotis falcata has a general East Asian dis­tribution, but it is never common. There are scat­tered collections of it as far as west as the Caucasus and as far east as the eastern part of Yakutia. In the Altai it occurs from 400 to 2200 m>m elev.