114 CONTRIBUTIONS FROM THE NATIONAL HERBARIUM. 



The bulbs and bright red berries are intensely acrid. They contain needle-like 

 crystals of calcium oxalate which readily penetrate the tongue when a piece is chewed, 

 causing swelling, as do the leaves of the common caladium or elephant's-ear (Colocasia 

 antiquorum escuknta), which also is a member of this family. Another name for the 

 species is Indian turnip. 



2. ACORUS L. 

 1. Acorus calamus L. Sweet flag. 



Marshes and along streams; common along the lower Potomac. May-June. Eastern 

 N. Amer.; also in Eur. and Asia. 



Known also as calamus or flag-root. The thick rootstocks, as well as the leaves, 

 have a pleasant flavor; they are used in medicine. 



3. ORONTIUM L. 

 1. Orontium aquaticum L. Golden club. 



In or at the edge of water; common and often verv abundant. Apr.-May. Eastern 

 U.S. 



i. SPATHYEMA Raf. 



1. Spathyema foetida (L.) Raf. Skunk cabbage. 



Swamps and wet woods; common. Feb.-Apr. Eastern N. Amer. (Symplocarpus 

 foetidus Nutt.) 



All parts of the plant have a strong, disagreeable odor which suggests the common 

 name. The flowers appear very early in the spring, usually before the leaves. A 

 group of plants in leaf as they appear in May in shown in plate 14. 



5. PELTANDRA Raf. 



1. Peltandra virginica (L.) Kunth. . Arrow arum. 



Swamps or shallow water; often very abundant. May-June. Eastern U. S. 



The leaves vary greatly in shape. In the typical form, which is the most common, 

 they are broadly halberd-shaped or arrow-shaped, with long acute lobes at the base. 

 In P. virginica helerophylla (Raf.) Tidestrom the leaves are very narrow and either 

 rounded at the base or with short rounded lobes. In P. virginica angustifolia (Raf.) 

 Tidestrom the leaves are still narrower, 4 cm. wide or less, and usually rounded at the 

 base. A detailed account of these forms has been published by Tidestrom. 1 



19. LEMNACEAE. Duckweed Family. 



Plants without roots; plant body distinctly rounded above, minute, without nerves. 



1. WOLFFIA. 

 Plants with roots; plant body distinctly flattened above, with one or more nerves. 

 Plant body 1-3-nerved, normally green throughout, bearing only one root. 



2. LEMNA. 

 Plant body 5-15-nerved, normally purple beneath, bearing several roots. 



3. SPIRODELA. 

 1. WOLFFIA Horkel. 

 1. Wolffia Columbiana Karst. 



Floating on the surface of spring-fed ponds on the Maryland shore of the Potomac 

 near Plummers Island; also in pools along the canal, near the District line. East- 

 ern U. S. 

 The smallest flowering plant of our region; not known to bloom locally. 



2. LEMNA L. Duckweed. 

 1. Lemna perpusilla Torr. 



Common on the surface of stagnant or slow-moving water. Blooms freely in mid- 

 summer, setting seed rather abundantly. Eastern U. S. (Probably L. minor of 

 Ward's Flora.) 



1 Rhodora 12: 45-50. pi. S3. 1910. 



