186 EVOLUTION OF PLANTS 
Anthurium. This bright-colored “spathe” serves here 
the purpose of the showy corolla of the higher forms. 
Somewhat higher in the scale are found plants whose 
flowers are made up of numerous but separate sporo- 
phylls. These may have carpels and stamens together 
in the same flower, or they may be separated, as in 
the common arrow-head (Sagittaria), (Fig. 45, H, J). 
In these there are also found the accessory. leaves, 
sepals (s) and petals (p), the latter often large and 
showy. These forms show certain analogies, both in 
the structure of the flowers and the tissues, with some 
of the lower Dicotyledons, especially the buttercup 
family (Ranunculaceze), and it has been suggested that 
the latter may have been derived from Monocotyledons 
of this type. 
Of the simplest of the Monocotyledons, the Naiad- 
acez, or pond-weeds, have been referred to. Other 
groups which are considered to be very primitive are 
the Cat-tail rushes (Typhacez), the Bur-reeds (Sparga- 
niacee), the Screw-pines (Pandanacee), as well as 
several other less-known groups. 
The Aroids (Aracee), of which the common calla lily 
is perhaps the best-known representative, show many 
evidences of being a primitive group, especially in the 
simplicity of the flowers, although there is considerable 
variety among them in this respect. They are for 
the most part tropical, although a few genera, Arum, 
Ariszeema, Symplocarpus, and others, are inhabitants of 
the temperate regions. Some of the tropical aroids are 
plants of considerable size, the largest being climbers, 
whose long stems may reach to the top of lofty trees. 
These climbing aroids are among the most striking of 
