460 MINNESOTA BOTANICAL STUDIES. 



BATRACHIUM S. F. GRAY, Nat. Arr. Brit. PI. 2: 720. 



1821. 



(Name from the Greek, in allusion to the aquatic habitat of 

 the plants.) 



Aquatic, or semi-aquatic perennial herbs ; leaves dissected or 

 lobed, submerged ones usually with filiform segments ; petioles 

 with stipular-dilated membranous bases : flowers solitary, op- 

 posite the leaves, rather small, white ; sepals usually 5 ; petals 

 usually 5, base often yellowish ; claw with a naked nectar pit; 

 stamens several or many : ovules oblique, compressed, not 

 margined, nearly beakless, transversely rugose. About 20 

 species, mostly of north temperate regions of the world. The 

 following are all that are found in North America. Section 

 BATRACHIUM DC. Syst. I : 233, under Ranunculus. 



KEY TO SPECIES. 



A. Aquatic leaves with filiform segments present ; receptacle hairy. 



B. Leaves all sessile or nearly so i. divaricatum. 



BB. Leaves, except the upper ones long-petioled. 



C. Emersed leaves always present, with segments broader than 



linear 2 . aquatile. 



CC. Emersed leaves if present only fleshy or nearly linear. 



3. trichophyllum. 



AA. Aquatic leaves none, or few, and with few divisions ; receptacle 

 glabrous. 



B. Styles minute, shorter than the ovaries 4. hederaceum. 



BB. Styles long and filiform 5. Lobbii. 



i. B. divaricatum WIMM. Fl. Schles. 10. 1841. 

 Ranunculus aquatilis /9. LINN. Sp. PL 556. 1753. 

 R. divaricatus SCHRANK, Baier. Fl. 2: 104. 1789. 

 R. circinalus SIBTH. Fl. Oxon. 175. 1794- 

 7?. aquatilus var. stagnatalis DC. Prod. I : 27. 1824. 

 Batrachium circinatum SPACH. Hist. Veg. 7*. 201. 1839. 

 R. stagnatalis WALLR. Sched. Crit. 285. 1848. 

 R. aquatilis var. divaricatus GRAY, Man. 2 ed. 7. 1856. 

 R. longirostris GODRON, Ess. 32. f. 9. 1862. 

 R. aquatilis var. longirostris LAWSON, Rev. Canad. 

 Ranunc. 43. 1870. 



Leaves sessile to the dilated stipule-like base, dissected into 

 rigid lobes spreading at right angles to the stem, not collapsing 

 when taken from the water ; no floating nor emersed leaves : 



