Isoetes L.

1. Isoetes L. View in CoL 2

Aquatic or terrestrial plants. Leaves terete or trigonous, subulate, occasionally flat and linear, often without stomata. Sporangia solitary, sessile, naked, or covered with a thin tissue (velum). The only genus in Europe. Literature: H. P. Fuchs, Nova Hedwigia , Beih. 3 (1962). 1 Leaf-bases not dark and horny, rarely persistent; plants aquatic

or, if amphibious, submerged for most of the year 2 At least | of sporangium covered by velum 3 Megaspores reticulate; ligule long, subulate 4. azorica 3 Megaspores not reticulate;liguleshort,triangular 4 Megaspores 530-700/2, rugose 1. lacustris 4 Megaspores 375-580//., spiny or tuberculate 5 Megaspores with rounded tubercles; stem 3-lobed

6 Leaf-bases not persisting; microsporessmooth orminutely papillose 5. boryana

6 Leaf-bases usually persisting as a papery, brown, scaly

‘ bulb ’; microspores ± spinose

7 Microspores with short spines; leaves yellow-green.

9. velata

7 Microspores with long setiform spines; leaves not yellow-green 10. tenuissima 5 Megaspores spinose; stems 2-lobed

8 Leaves compressed; membranous margin not extending up leaf 2. setacea

8 Leaves terete; membranous margin extending up leaf for I of its length 3. brochonii 2 Sporangiumnot coveredbyvelum 9 Megasporesminutelypapillosewithinconspicuousridges;

microspores smooth 6. delilei 9 Megasporesverrucosewithprominentridges; microspores spinose 10 Leaves 30-80 cm; plants aquatic 7. malinverniana 10 Leaves 10-25 cm; plants amphibious 8. heldreichii 1 Leaf-bases dark, shiny and persistent; plants terrestrial (if submerged then only for a short period in winter)

11

Megaspores 320-560//, tuberculate

11. histrix 11

Megaspores 600-800//, reticulate

12. durieui