GENUS 3. 



DUCKWEED FAMILY. 



i. Wolffia columbiana Karst. Columbia Wolffia. 

 Fig. 1127. 



Wolffia columbiana Karst. Bot. Unters. i: 103. 1865-67. 



Thallus spherical or subellipsoid, i"-S" long, with a 

 limited number of stomata (i to 6), loosely cellular and 

 clear green throughout, not dotted nor gibbous. 



Floating as minute alga-like grains just beneath the surface 

 of the water in stagnant ponds, pools and shallow lakes, On- 

 tario to Connecticut and New Jersey, west to Minnesota and 

 Missouri, south to Louisiana. Also in Mexico and South 

 America. June-July. 



2. Wolffia punctata Griseb. 

 1128. 



Dotted Wolffia. 



W. punctata Griseb. Fl. Br. W. I. 512. 1864. 



Thallus oblong, smaller than the last, "-J" long, flattish, 

 densely cellular, with numerous stomata and dark green 

 above, gibbous, more loosely cellular, with fewer stomata 

 and paler beneath; brown-dotted throughout with minute 

 pigment cells. 



Floating on the surface of stagnant waters, Ontario to Mich- 

 igan, south to Tennessee. Jamaica. Has been confused with 

 W. brasiliana Wedd. June-July. 



9 9 

 8?9 



3. Wolffia papulifera Thompson. Pointed 

 Duckweed. Fig. 1129. 



Wolffia papulifera Thompson, Ann. Rep. Mo. Bot. 

 Card. 9 : 20. pi. 4D. 1897. 



Thallus slightly unsymmetrical, obliquely broadly 

 ovate, about i' broad, the apex rounded, the 

 upper surface flat at the margin, gradually ascend- 

 ing into a prominent conic papule on the median 

 line, brown-punctate, the under surface strongly 

 gibbous, less punctate; stomata numerous on the 

 upper surface ; flower and fruit unknown. 



Floating, with the entire upper surface exposed to 

 the air, Kennett and Columbia, Mo. 



4. WOLFFIELLA Hegelm. Engler's Bot. Jahrb. 21 : 303. 1895. 



Thallus thin, unsymmetrical, rootless, curved in the form of a segment of a band, punc- 

 tate on both surfaces with numerous brown pigment-cells. Pouch opening as a cleft in the 

 basal margin of the thallus, a stipe attached to its margins. Flowers and fruit unknown. 

 [Diminutive of Wolffia.} 



About 7 species, mostly of tropical regions. Besides the following, 2 others are known from 

 western North America. Type species: Wolffiella oblonga (Phil.) Hege'.m. 



i. Wolffiella floridana (J. D. Smith) Thompson. 

 Florida Wolffiella. Fig. 1130. 



Wolffia gladiata var. floridana J. D. Smith, Bull. Torr. Club ^ : 64. 



1880. 

 Wolffia floridana J. D. Smith ; Hegelm. Engler's Bot. Jahrb. 21 : 



Wolffiella floridana Thompson, Ann. Rep. Mo. Bot. Card. 9: 17. 



1897. 



Thalli solitary, or commonly coherent for several genera- 

 tions forming densely interwoven masses, strap-shaped, scythe- 

 shaped, or doubly curved, tapering from the rounded oblique 

 base to a long-attenuate apex, 2*"-5" long, 14-21 times as 

 long as wide; basal portion of the long stipe persistent, the 

 pouch elongated-triangular, or the upper angle rounded. 



Georgia and Florida to Missouri, Arkansas and Texas. 

 29 



