LEMNACEAE 229 



fluent at maturity. Ovary 3-4-celled, oblong. Ovules 2-8, anatropous. Fruits gelatinous, 

 2-3-celled. Seeds several. Endosperm copious. Calamus. Sweet Flag. 



1. Acorus Cdlamus L. Rootstocks horizontal, pungent-aromatic : leaves several) 

 5-20 dm. tall ; blades linear, attenuate, sharp-edged, bright green : scape quite similar to 

 the leaves, often narrower : spathe similar to the leaves, extending 2-8 dm. beyond the 

 spadix, attenuate, erect: spadix elongated-conic, 3-8 cm. long, yellowish, ascending or 

 spreading, densely flowered : fruits 4-5 mm. long, lustrous. 



In marshes and springy places, Xova Scotia to Minnesota, Florida and Texas. Spring and summer. 



Family 2. LEMNACEAE Dumort. Duckweed Family. 



Perennial floating herbs, consisting chiefly of very small, often minute, fleshy 

 structures, representing modified stems, sometimes with 1 or several roots. 

 Vegetative reproduction is accomplished by lateral branching. Propagative 

 pouches 1 or 2 in each body. Flowers monoecious, one or two staminate and 

 one pistillate, arising from a point in a propagative pouch. Staminate flowers 

 consist of 1 stamen. Anthers 1-2-celled : sacs opening lengthwise or transversely. 

 Pollen of minutely barbellate spherical grains. Pistillate flowers consist of 1 car- 

 pel, stigmatic at the apex. Ovules one or several. Fruit a utricle. 



Plant-body much elongated or subglobose, not disk-like, rootless : propagative pouch solitary. 



Plant-body very thick or subglobose. 1. Wolffia. 



Plant-body thiii, tongue-like or saber-form. 2. Wolffiella. 



Plant-body disk-like, with 1 root or several roots : propagative pouches 2. 



Plant-body inconspicuously nerved : root solitary, without a fibro-vascular bundle. 3. Lemna. 



Plant-body conspicuously nerved : roots several.each witha fibro-vascular bundle. 4. Spirodela. 



1. "WOLFFIA Horkel. 

 Plant-body much thickened or subglobose, with the stipe attached beneath the propa- 

 gative pouch near the margin. Propagative pouch funnelform, opening near the base of 

 the plant-body. Spadix of 1 staminate and 1 pistillate flower bursting through the upper 

 surface of the plant-body. Anther 1-celled. Ovule 1, orthotropous. Utricle smooth. 



Plant-body smooth, somewhat flattened above, gibbous beneath, brown-punctate. 1. W. pmictata. 

 Plant-body ellipsoidal or globose, with 2-3 papules on dorsal surface, not punctate. 2. Tl''. Columbiana. 



1. Wolffia punctata Griseb. Plants solitary ; body boat-like, elliptic to ovoid-ob- 

 long, 0.58-0.82 mm. long, flat, or nearly so above, gradually rising at the apex, whole 

 surface punctate with brown cells : ti.ssue various ; lower portion of the plant-body com- 

 posed of larger cells than the upper. [ TF. Brasiliensis |of Am. Auth., not of Wedd.] 



In still or stagnant water, Ontario to Michigan, Illinois and Tennessee. Summer. 



2. WolCBa Columbiana Karst. Plants solitary ; body globose to ellipsoidal, 0.48- 

 1 mm. long, the upper surface convex, with a row of inconspicuous papillae only a small 

 portion emersed, this with 1-10 stomata, not punctate : tissue of uniform large cells. 



In lakes and pools, Massachusetts to Ontario, Minnesota, Florida and Louisiana. Spring to fall. ^ 



2. WOLFFIIJLLA Hegelmaier. 



Plant-body thin, tongue-shaped or saber-form, with the stipe attached on the margin of 

 the propagative pouch. Roots wanting. Propagative pouch solitary, triangular, opening 

 by a slit in the basal margin of the plant-body. Inflorescence and fruit unknown. 



1. WolfBella Floridana (J. D. Smith) C. H. Thompson. Plants minute, solitary or 

 usually several generations cohering, thus forming dense mats ; body elongated, attenuate 

 from the base to the slender apex, 5.5-8.5 mm. long, hollow except near the apex. 



In still or stagnant water, Missouri to North Carolina, Georgia, Florida and Texas. Spring to fall. 



3. LEMNA L. 



Plant-body disk-like, with 1-5 inconspicuous nerves, the stipe attached to the basal mar- 

 gin. Roots solitary, each with a blunt or pointed root-sheath. Propagative pouches 2, 

 triangular, opening by slits in either margin of the basal part of the thallus. Spadix of 

 1 pistillate and 2 staminate flowers, arising' from the propagative pouches. Anthers 2- 

 celled : sacs opening transversely. Ovary with 1 orthotropous and araphitropous ovule or 

 2-6 anatropous ovules. Utricle somewhat flattened, often ribbed. Duckweed. 



Plant-bodies long-stipitate, forming large submerged masses. 1. L. trimlca.. 



Plant-bodies sessile, or short-stipitate, floating, more or less detached. 

 Plant-body symmetrical or nearly so. 



Plant-body oblong-obovate : utricle lenticular. 2. L. minor. 



