1976 A TEXTBOOK OF THEORETICAL BOTANY 



The calyx is composed of three sepals which are imbricated in the 

 bud and generally green in colour. 



The corolla consists of three petals, imbricated in the bud and usually 

 white or violet in colour and often of large size. 



The androecium is made up of either six or an indefinite number of 

 stamens whose anthers may dehisce either introrsely or extrorsely. 



The gynoecium is composed of a variable number of carpels, rarely 

 less than six, which are free and developed on a somewhat conical receptacle. 

 Each carpel contains usually a single, or rarely several, anatropous or campylo- 

 tropous ovules. The style is persistent. 



The fruit is an etaerio of akenes or of follicles, and hard, woody or 

 leathery in consistency. 



The seed contains a large horseshoe-shaped embryo, with a long 

 cotyledon and a large hypocotyl ending in a short blunt radicle. The seed 

 is non-endospermic. 



The family contains about a dozen genera and includes some fifty 

 species occurring in temperate and tropical regions of the northern hemi- 

 sphere. The limits of the family have been variously interpreted, more 

 particularly on the question whether the Butomaceae should be included 

 in the Alismaceae, or separated from it. 



Anatomically the Alismaceae, as here interpreted, exhibit certain 

 common features of interest, more particularly in the presence, both in the 

 stems and leaves, of an intercellular laticiferous system containing an oil 

 emulsion. In the rhizomes oi Alisma plant ago and in the tubers of Sagittaria 

 sagittifoUa these laticiferous canals form a network which is closely con- 

 nected with the vascular bundles. In certain tropical genera the laticiferous 

 system is so extensive in the leaves that it forms bright transparent dots in 

 the green tissue of the blade, always in close association with the vascular 

 bundles. 



The stomata are very variable in distribution according to whether 

 the leaf is aerial, floating or submerged, a fact which also aflFects the distri- 

 bution of mechanical tissue. 



Economically the family is of little importance although the tubers of 

 Arrowhead are a potential source of carbohydrate material. In Germany 

 they are sometimes used to feed pigs, while the ever-careful Chinese culti- 

 vate the plant for the sake of the tubers and have produced a variety in which 

 the tubers reach the size of about 3 to 4 in. in diameter. Tubers of the 

 related S. variabilis are called Swan Potatoes and are said to be eaten by the 

 American Indians. 



The family is not usually subdivided into separate tribes. The follow- 

 ing may be cited as the more important genera: Alisma with one species 

 found in north temperate regions and Australia; Sagittaria with about 

 thirty species occurring mostly in America; Damasoniiim with three species 

 occurring in California, Australia, Tasmania and in Europe; Elisma with a 

 single European species; and Echinodorus, with twenty species in America 

 and Africa, one of which occurs in Britain. 



