Equisetum Key

New England Isoëtes Key

1. Leaves erect, stiff, brittle; macrospores with minimal ornamentation – I. prototypus

(northern, rare)

1. Leaves pliable; macrospores with prominent ornamentation → 2

2. Macrospores with distinct spines (most common taxon by far) – I. echinospora

2. Macrospores ornamented with ridges, interconnected or not → 3

3. Macrospore ornamentation reticulate, forming regular cells → 4

otherwise → 5

4. Ornamentation ridges rounded, not much taller than wide, girdle smooth – I. acadiensis

4. Ornamentation ridges much taller than wide, no visible girdle – I. engelmannii

5. Macrospores homogeneous in size and shape → 6

5. Macrospores of varying size and shape, or proximal zone flattened [hybrid]

6. Macrospore diameter average > 0.6mm – I. lacustris

6. Macrospore diameter < 0.6mm → 7

7. Leaves mostly medium green – I. riparia

7. Leaves mostly dark green – I. tuckermanii