| | 1. Tip of plant body clearly pointed, upper surface distinctly flattened — dead plants dotted with brown pigment cells |
| W. borealis |
| | 1' Tip of plant body rounded, upper surface ± rounded (except W. arrhiza) |
| |
| | 2. Upper surface of mature vegetative plant body with a prominent bump; dead plants dotted with brown pigment cells |
| W. brasiliensis |
| | 2' Upper surface of mature vegetative plant body smooth; brown pigment cells 0 |
| |
| | 3. Upper surface dark green, distinctly flattened; stomates generally 15–100 |
| W. arrhiza |
| | 3' Upper surface transparent green, ± rounded; stomates 1–10(30) |
| |
| | 4. Plant body 0.8–1.3 mm, almost spheric, most of upper surface clearly rounded, the top flat |
| W. columbiana |
| | 4' Plant body 0.4–0.8 mm, longer than wide, upper surface barely rounded throughout |
| W. globosa
|