54 LEMNACEAE 



Family 15. ABACEAE Neck. 

 Herbs with dioecious, monoecious or perfect flowers on a spadix sur- 

 rounded by a spathe. Perianth absent or of 4-6 sepals. Stamens 4-10. 

 Ovary with 1-several ovules. Fruit berry-like. 



Leaves compound. 1. Aeisabma. 



Leaves simple and rush-like. 2. Acorus. 



1. ARISAEMA Mart. 

 Perennial from an acrid corm. Flowers dioecious or monoecious at the 

 base of the spadix. Perianth absent. Staminate flowers composed of a 

 few, nearly sessile, 2- 4-celled anthers, the pistillate of a 1-celled ovary 

 containing 1-8 ovules. 



Leaf divided into 3 leaflets. 1. A. triphyllum. 



Leaf divided into 7-11 leaflets. 2. A. Dracontium. 



1. A. triphyllum (L.) Torr. Jack-in- the-Pdlpit. Leaves 1-2, with 

 3 elliptical-ovate leaflets : spathe hooded and curving over the spadix, 

 opened at the throat : spadix 2'-3'' long, club-shaped. — Eather common 

 in rich damp woods. April-May. 



2. A. Dracontium (L. ) Schott. Gebbn Dragon. Leaf usually 

 solitary, divided into 7-15 oblong-lanceolate leaflets : spathe oblong, 

 acuminate and convolute at the apex, much exceeded by the long (l'-9') 

 and slender tip of the spadix. — In woods throughout. Well distributed, 

 but nowhere abundant. May. 



2. ACORUS L. 



Herbs from long running, pungent aromatic rootstocks. Scapes 3- 

 angled, similar to the leaves. The spadix seemingly lateral, the spathe 

 appearing like a continuation of the culm. Flowers perfect, densely 

 covering the spadix. Sepals and stamens 6. Ovary 2-4-celled with several 

 ovules in each cell. 



1. A. Calamus L. Sweet Flag. 2°-5° high. — Very abundant in a 

 swamp near the Little Blue River east of Atherton ; Levasy. May. 



Family 16. LEMNACEAE Dumort. 

 Minute floating aquatics, consisting of a frond, bearing flowers from 

 the edge or surface. Flowers monoecious, consisting of a single stamen 

 or a single pistil. Ovary bearing 1-6 erect ovules. The species are all 

 known as "Duckweeds." 



Frond with several rootlets. 1. Spirodela. 



Frond with one rootlet. 2. Lemna. 



Frond without rootlets. 3. Wolffia. 



1. SPIRODELA Schleid. 



Fronds 7-12-nerved. Ovary bearing two ovules. 



1. S. polyrhiza (L.) Schleid. Fronds 2"-5''' long, round-obovate, 

 green above, purplish beneath, usually 7-nerved.— Often very common in 

 ponds and ditches. 



