1. Marginal teeth of leaves sharp and large, 2 or multicellular; opercula not rostrate........................ 2
1. Marginal teeth of leaves blunt and small, usually unicellular; opercula rostrate..................................5
2. Leaves narrowly elliptical or oblong-lanceolate; costae percurrent...................................................3
2. Leaves broadly obovate or rounded-oblong; costae ending below the apex........................................4
3. Leaves narrowly oblong-lanceolate; margins serrate throughout; leaf cells nearly elliptical, irregularly arranged.......................................................................................................2. P. arbuscula
3. Leaves narrowly elliptical or oblong; margins serrate above the mid-leaf; leaf cells hexagonal, regularly arranged.................................................................................................... ...16. P. venustum
4. Leaves oblong or nearly rounded; leaf cells rounded-quadrate, irregularly arranged........ 5. P. drummondii
4. Leaves broadly obovate or elongate-obovate; leaf cells hexagonal, regularly arranged....... 9. P. japonicum
5. Leaves oblong, rounded-elliptical, ovate or ligulate; leaf apices obtuse, truncate or apiculate..............6
5. Leaves ovate, obovate, elliptical or oblong-lanceolate; leaf apices acute or cuspidate.......................10
6. Juxtacostael cells with 1 row of the cells hyaline, distinctly larger than adjacent cells.......10. P. maximoviczii
6. Juxtacostael cells without any hyaline cells, not particularly larger than adjacent cells............................... 7
7. Leaves rounded-elliptical or ovate, scarcely undulate, obtuse at apex; margins bordered by 4–6 rows of elongated cells........................................................................17. P. vesicatum
7. Leaves narrowly oblong or ligulate, undulate, rounded-truncate at apex; margins hardly bordered or bordered by (1–)3–4 rows of rectangular or elongate cells................................................................................. 8
8. Leaf margins hardly bordered or only at base bordered by 1–2 rows of more or less rectangular cells; costae ending below the apex................................................................6. P. elimbatum
8. Leaf margins bordered by 3–4 rows of elongated cells; costae percurrent....................9
9. Leaf bases decurrent; leaf cells ca.10–25 µm in diameter.............................12. P. rhynchophorum
9. Leaf bases not decurrent; leaf cells ca. 30–50 µm in diameter......................13. P. rostratum
10. Leaves typically elliptical; margins bordered by 4–8 rows of narrowly elongate cells...... 7. P. ellipticum
10. Leaves broadly ovate, oblong or ovate-lanceolate; margins bordered by 2–4 rows of elongate cells..... 11
11. Costae ending below the apex.................................................................................12
11. Costae percurrent...................................................................................................13
12. Leaves rounded-ovate or obovate, decurrent at base..............................3. P. confertidens
12. Leaves broadly elliptical or broadly ovate, not decurrent at base..............14. P. succulentum
13. Leaves broadly ovate or ovate-lanceolate; leaf cells isodiametric, ca. 20–35 µm wide...............14
13. Leaves broadly elliptical or oblong-elliptical; leaf cells hexagonal-elliptical, ca. 40–70 µm × 25–45 µm 15
14. Leaves mostly light green, shiny, elliptical or narrowly obovate; leaf cells hexagonal, walls not thickened at corners.......................................................................................................................... 1. P. acutum
14. Leaves mostly dark green, dull, elliptical or ovate; leaf cells rounded-hexagonal, walls thickened at corners.........................................................................4. P. cuspidatum
15. Leaf margins entire, indistinctly bordered..................................................8. P. integrum
15. Leaf margins serrate, distinctly bordered..................................................16
16. Leaf apices acute; marginal teeth short, blunt; cell walls not or indistinctly porose............ 11. P. medium
16. Leaf apices obtuse to mucronate; marginal teeth long, sharp; cells walls distinctly porose.....15. P. tezukae