Genus i. 



MARSILEA FAMILY. 



37 



i. Marsilea quadrifdlia L European 

 Marsilea or Pepperwort. Fig. 85. 



Marsilea quadrifolia L. Sp. PI. 1099. 1753. 



Rootstock slender, buried in the muddy bot- 

 toms of shallow lakes or streams. Petioles usu- 

 ally slender, 2'-$' high, or when submerged 

 sometimes elongated to 1° or 2°. Leaflets mostly 

 triangular-obovate, variable in outline, 3"-8" 

 long, 2"-6" wide, glabrous or rarely with scat- 

 tered hairs when young, the margins entire; 

 sporocarps 2 or rarely 3 on a branching peduncle 

 which is attached to the petiole at its base, 

 covered with short yellowish-brown hairs when 

 young, becoming glabrous and dark purple when 

 mature; sori 8 or g in each valve. 



Bantam Lake, Litchfield Co., Conn. ; thence intro- 

 duced into other parts of the country, from Massa- 

 chusetts to Maryland. Native of Europe and Asia. 



2. Marsilea vestita Hook. & Grev. 

 Hairy Pepperwort. Fig. 86. 



M. vestita Hook. & Grev. Ic. Fil. pi. 159. 1831. 



Marsilea mucronata A. Br. Amer. Journ. Sci. 

 (II.) 3: 55. 1847. 



Rootstocks slender, creeping. Petioles slen- 

 der, 2'-s' high ; leaflets similar to those of the 

 preceding species, entire or toothed; sporo- 

 carps 2"-4 r " long, 2" -3" wide, with a short 

 raphe, a short and blunt lower tooth and an 

 acute and sometimes curved upper one, densely 

 covered with soft spreading narrow hair-like 

 scales or (in the forms known as M. mucro- 

 nata) these short and appressed or almost 

 wanting; sori 6-1 1 in each valve. 



In wet sand or in shallow ditches, Florida to 

 Kansas, Arizona and Mexico, California and 

 British Columbia. 



Family 7. SALVINIACEAE Reichenb. Consp. 30. 1828. 



Salvinia Family. 

 Small floating plants with a more or less elongated and sometimes branching 

 axis bearing apparently 2-ranked leaves. Sporocarps soft, thin- walled, borne 2 or 

 more on a common stalk, i-celled, with a central often branched receptacle, which 

 bears megasporanges containing a single megaspore or microsporanges containing 

 numerous microspores. The megaspores germinate into prothallia which bear 

 archegones, the microspores into prothallia which bear antherids. 



The family consists of two genera. 

 Leaves 6"-g" long, 2-ranked, on mostly simple stems. 

 Leaves minute, closely imbricated on pinnately branching stems. 



1. Salvinia. 



2. Azolla. 



i. SALVINIA Adans. Fam. PI. 



2: 15. 1763. 



Floating annual plants with slender stems bearing rather broad 2-ranked leaves, these 

 finely papillose on the upper surface. Sporocarps globose, depressed, 9-14-sulcate, mem- 

 branous, arranged in clusters, I or 2 of each cluster containing 10 or more sessile mega- 

 sporanges, each containing a single megaspore, the others containing numerous smaller globose 

 pedicelled microsporanges with very numerous microspores. [Name in honor of Antonio 

 Maria Salvini, 1633-1729, Italian scientist.] 



About 13 species widely distributed. Only the following, the generic type, in the United States. 



