| 1 | Fronds repeatedly dichotomous |
| 1' | Fronds simple. |
| 2 | Sorophores 2.5-5 cm long, all attached close together at apex of frond; frond 2 mm or more wide. |
| 2' | Sorophores much shorter, fronds narrower. |
| 3 | Sporangia in four rows on the sorophores; one row of stomata on each wing of the frond. |
| 3' | Sporangia in two rows on sorophores; stomata in two rows on each wing of the frond. |
| 4 | Edges of sorophores smooth and glabrous. |
| 4' | Edges of sorophores irregularly lobed, the lobes bearing coarse hairs. |
| 5 | Fronds more than 1 mm wide, with distinct fiat wing on each side of costa; no hairs with sporangia. |
| 5' | Fronds less than 1 mm wide, wing very slightly developed; hairs present with sporangia |
| 6 | Costa very prominent on lower surface; stomata in each row very close together |
| 6' | Costa hardly prominent on lower surface; stomata in each row rather widely spaced. |
| 7 | Sorophores attached along the distal 10-20 mm of the axis of the frond; upper surface of frond deeply grooved, lower surface evenly rounded and bearing superficial rows of stomata. |
| 7' | Sorophores attached along the distal 5-10 mm of the axis of the frond; upper surface of frond slightly grooved, stomata in two slight grooves on the distinctly flattened lower surface |
