LXXIX. ALlSMACEJi. 481 



t The genera are not numerous, but several of them are dispersed over 

 the greater part of the world. 



Perianth-segments all nearly equal, large and coloured, flower- 

 stem tall, with a large terminal umbel 1. BOfOMUS. 



Perianth-segments 3 small and herbaceous, 3 large and coloured. ' 



Flowers opposite or whorled, in a terminal raceme, umbel, or 

 panicle. 



Carpels and stamens numerous. Leaves sagittate . . .2. SAQITTARIA. 

 Carpels numerous. Stamens 6. Leaves ovate or narrow . . 3. ALISMA. 

 Carpels 8. Stamen* 8. Leaves ovate or oblong . .4. DAMASONIUM. 



I. BUTOMUS. BUTOME. 



A single species, distinguished from Alisma as a genus, or by some 

 botanists as an independent family, chiefly on account of the ovary, 

 which has several ovules in each carpel. 



1. B. umbellatus, Linn. (fig. 972). Flowering Rush. A. perennial, 

 with a thick, creeping rootstock, and long, erect, sedge-like triangular 

 radical leaves, broad and sheathing at the base. Flower-stem leafless, 

 2 to 4 feet high, thick and rush-like, bearing a large umbel of showy, 

 rose-coloured flowers, with 3 lanceolate, thin bracts at its base. Pedi- 

 cels 3 to 4 inches long, often 20 to 30 in the umbel. Perianth fully an 

 inch diameter, of 6 ovate, spreading, nearly equal segments. Stamens 

 9. Carpels 6, erect, tapering into short styles, seeds numerous minute. 



In watery ditches, and still waters, over Europe and temperate Asia, 

 except the extreme north. Central and southern England, rare in 

 England, introduced only in northern England and Scotland. Fl. 



II. SAGITTABIA. ARROWHEAD. 



Aquatic herbs, differing from Alisma in their unisexual flowers, the 

 males with numerous stamens, the females with very numerous small 

 carpels in a dense head. 



Besides the common species, there are several from North and South 

 America, and eastern Asia. 



1. S. sagittifolia, Linn. (fig. 973). Common A. A perennial, 

 with a creeping rootstock, forming bulb-like tubers. Leaves radical, 

 rising out of the water on very long stalks ; the blade 6 to 8 inches 

 long, sagittate ; the lobes of the base nearly as long as the ter- 

 minal one, all pointed, but varying much in width. Flower-stem 

 leafless, erect, longer than the leaves, bearing in its upper part several 

 distant whorls of rather large, white flowers ; the 3 inner segments of 

 the perianth twice as long as the 3 outer green ones ; the upper flowers 

 usually males, on pedicels to 1 inch long ; the lower ones females, on 

 shorter pedicels. 



In watery ditches, and shallow clear ponds and streams, dispersed 

 over the greater part of Europe and temperate Asia, to the Arctic 

 regions. In Britain, limited to England and Ireland, naturalised in 

 Scotland. Fi. rummer and autumn. 



