Key to the Bolivian species of Isoëtes

1 Plants of eastern lowlands <500 m ................................................................................................................................................... 2

- Plants of Andean habitats 2500–5200 m .......................................................................................................................................... 4

2 Plants small (leaves 10–25 cm long); megaspores small (<425 μm) with verrucate (mounded) ornamentation on coarsely ‘spidery’perispore; equatorial ridge straight .......................................................................................................... I. santacruzensis

- Plants large (leaves 15–28 cm long); megaspores large (>450 μm) with tuberculate or baculate ornamentation on finely ‘spidery’or granular perispore; equatorial ridge undulate ................................................................................................................................... 3

3 Megaspores tuberculate with tubercules evenly distributed, broad and rounded; equatorial ridge broad, straight to inconspicuously undulating; perispore finely covered in a tri-dimensional mesh of fused bars (spidery); microspores densely echinate with conspicuous broad-based spines in broken-reticulate pattern ........................................................................... I. afloramientorum

- Megaspores baculate, if tuberculate, tubercules irregularly distributed, narrow and slightly tapered; equatorial ridge narrow, conspicuously undulating; perispore granular; microspores typically plain ............................................................... I. panamensis

4 Rootstocks vertically elongate; leaves 50–200 per rootstock, 3–5(7.5) cm long; plants of cushion bogs ...................... I. andicola

- Rootstocks globose; leaves <40 per rootstock, 4–25 cm long; plants of lakes, pools, streams, and marshes .................................. 5

5 Leaves turgid, stiffly erect; velum covering (20)70–100% of each sporangium ............................................................................. 6

- Leaves flaccid, lax to weakly erect; velum covering 0–80(100)% of each sporangium .................................................................. 7

6 Leaves to 20 per rootstock, 4–9 cm long, bright green, basally without dark pigmentation; rootstocks globose to slightly horizontally elongate; megaspores usually rugulate, rarely smooth ...................................................................................................... I. herzogii

- Leaves to 40 per rootstock, 9–16 cm long, dark green, usually basally with dark brown to nearly sclerotic pigmentation; rootstocks globose to extensively horizontally elongate; megaspores smooth .................................................................................... I. lechleri

7 Velum covering (5)60–80(100)% of each sporangium; gemmae absent; megaspores smooth to minutely tuberculate or cristate; microspores verrucate .................................................................................................................................................... I. boliviensis

- Velum covering 0–10(40)% of each sporangium; gemmae present at leaf bases; megaspores tuberculate, rarely almost smooth or rugulate; microspores echinate ..................................................................................................................................... I. eshbaughii