1922] 



PFEIFFER MONOGRAPH OF THE ISOETACEAE 105 



KEY TO SPECIES 



A. Forms with 3-lobed corms; megaspores marked with few to many large 

 rounded tubercles; microspores rough; leaves mostly slender, usually 

 with peripheral strands and stomata. Chiefly forms of the eastern hemis- 

 phere. 



a. Velum none or little developed, 

 a. Terrestrial forms. 



I. Leaves few, velum none 1. I. Welvjitschii 



II. Leaves many, velum covering %-% of sporangium. 2. I. aequinoctialis 

 p. Forms not terrestrial in habit. 



I. Megaspores more than 400^ in diameter. 



1. Leaves few in number, less than 20. 

 * Stomata present. 



tPeripheral strands well-developed 3. I. Scliweinfurthii 



ttPeripheral stranda variable (none-6) 3.5. I. ovata 



**Stomata absent 4. I. Heldreichii 



2. Leaves more than 20 in number. 

 *Megaspores 480-540 /j. in diameter, with large 



tubercles 5. I. coromandelina 



**Megaspores 565-680 ^ in diameter, with num- 

 erous smaller tubercles 6. I. setacea 



***Megaspores 660-800 /* in diameter, with 



elongated coarse processes .. 7. I. Malinverniana 



II. Megaspores chiefly less than 400 ^ in diameter. 



1. Leaves not filiform, more than 25 cm. long 8. I. cubana 



2. Leaves filiform, less than 25 cm. long. 



*Megaspores gray 9. I. nigritiana 



**Megaspores white 10. I. adspersa 



b. Velum complete or nearly so. 



a Megaspores with few coarse warts. 



I. Megaspores becoming dark when wet. 



1. Coarse plants, more than 15 leaves, more 



than 12 cm. in length 11. I. Boryana 



2. Finer plants, less than 15 leaves, less 



than 15 cm. in length _.-- -12. I. tenuissima 



II. Megaspores creamy when wet. 



1. Leaves chiefly less than 24 cm. in length. 

 *Leaves slender and short. 



t Leaves more than 10 cm. long. 



o Megaspores more than 480^ in diameter 13. I. dubia 



oo Megaspores less than 480 fj, in diameter 15a. I. velata var. 



Perralderiana 



ttLeaves less than 5 cm. long 14. I. olympica 



**Leaves coarser, chiefly less than 24 cm. in length, 



rarely longer 15. I. velata 



2. Leaves longer, chiefly more than 22 cm. in Iength__i6. I. tegulensis 

 j9. Megaspores with more numerous regular tubercles. 



I. Leaves more than 15 cm. long, more than 10 in number ..17. I. alpina 

 II. Leaves less than 15 cm. long, less than 10 in number -.18. I. Kirkii 



B. Forms with 2- or 3-lobed corms; megaspores rarely smooth, 



usually marked with numerous small tubercles, sometimes 

 confluent; microspores smooth or rough; peripheral strands 

 and stomata variable among species. 

 a. Corms 3-lobed. 



a. Velum none or little developed. 



I. Leaves short, less than 11 cm. in length. 



1. Stomata absent 19. I. Chinnii 



2. Stomata present. 



*Megnspores less than 470 /j. in diameter 20. I. Drummondii 



**Megaspores more than 420^ in diameter 21. I. amazonica 



