THE DICOTYLEDONES 



1717 



CENTROSPERMAE 



The Centrospermae are Archichlamydeae with either hermaphrodite, 

 monoecious or dioecious flowers, which are actinomorphic and usually 

 pentamerous. The perianth is either single or double. The stamens are 

 in one or two whorls and are generally either five or ten in number. In 

 the former case they are generally opposite the petals. The ovary is usually 

 superior, composed of from one to five carpels which are united to form a 

 unilocular, rarely multilocular, ovary containing from one to many campylo- 

 tropous ovules. The fruit is generally a capsule or nut, rarely a berry. 

 The embryo is large and curved and the seed contains perisperm. 



It is largely upon the campylotropous ovules, the curved embryo and 

 the presence of perisperm that the apparently dissimilar genera are grouped 

 together. 



In the older classifications this order contained the following principal 

 families: Chenopodiaceae, Amarantaceae, Phytolaccaceae, Portulacaceae, 

 Aizoaceae, Nyctaginaceae and Caryophyllaceae. In more recent treatments, 

 such as that of Hutchinson, the order is split up into a number of distinct 

 orders. Thus the Chenopodiales are considered to include the Chenopo- 

 diaceae, Phytolaccaceae and Amarantaceae; the Caryophyllales include 

 the Caryophyllaceae, Aizoaceae and Portulacaceae, 

 while the Nyctaginaceae are excluded from the 

 order. In Hutchinson's view the Caryophyllales 

 are the more primitive group, arising from the 

 Ranales through the Saxifragaceae; while the 

 Chenopodiales as well as the Polygonales are con- 

 sidered to be derived from them. 



We shall consider the Chenopodiaceae and 

 Caryophyllaceae in detail, but first will briefly 

 review the other families mentioned above. 



The Phytolaccaceae include herbs, shrubs 

 and trees with large, alternate leaves, occurring 

 mostly in the tropics and subtropics. The carpels 

 are free, which is exceptional in the order. 

 Phytolacca dioica is used as a shade tree in Spanish 

 countries and is known as Bella Sombra. Others, 

 herbaceous species of the same genus, are some- 

 times cultivated in gardens (Fig. 1591). Secondary 

 thickening is by successive bundle rings. 



The Portulacaceae are herbs and under 

 shrubs which are often succulent. They are mainly 

 American in origin. Among those cultivated for 

 ornamental purposes may be mentioned Portiilaca 

 grandi flora (Sun Plant), an annual from Brazil; 

 Anacampseros arachnoides, a succulent greenhouse plant from the Cape ot 

 Good Hope, and species of Calandrinia (Rock Purslane), which are pink 



''Xi »■* ik 



Fig. 1 591. — PhytcLicca 

 decandra. 

 Inflorescence. 



