406 PLANT MORPHOLOGY 



Rubiales. This order consists of over 5,000 species of herbs and woody- 

 plants distributed among 5 families, by far the largest being the Rubia- 

 ceae, to which belong coffee iCoffea) and Cinchona. The Caprifoliaceae, 

 another family, is represented by the honeysuckles (Lonicera), Viburnum, 

 and the elders (Samhucus) . The flowers are regular or irregular, tetram- 

 erous or pentamerous, tetracyclic, anisocarpic, epigynous, and syncar- 

 pous. They have usually two or three carpels. The calyx is reduced. 

 This order shows a resemblance to the Umbellales. 



Campanulales. This is the culminating order of Metachlamydeae. 

 It includes 8 families and 16,000 species, about 13,000 of which belong to 

 the Compositae, the largest family of dicotyledons. A few well-known 

 genera are goldenrod (Solidago), Aster, sunflower (Helianthus), Chrysan- 

 themum, thistle (Cirsium), dandelion (Taraxacum) , lettuce (Lactuca), etc. 

 Other familiar families are the Cucurbitaceae, Campanulaceae, and Lobe- 

 liaceae. The flowers are regular or irregular, pentamerous, tetracyclic, 

 anisocarpic, epigynous, and syncarpous. They have two or three carpels. 

 The calyx is reduced. A special feature is the tendency of the five 

 stamens to be united in various ways. The flowers of the Compositae are 

 organized to form a compact head surrounded by an involucre of many 

 bracts. The head is usually composed of peripheral ray flowers and cen- 

 tral disk flowers. 



3. MONOCOTYLEDONEAE 



The monocotyledons are generally regarded as having been derived 

 from the Ranales region of the Archichlamydeae. In the lower orders the 

 floral parts fluctuate in number and are more or less spiral in arrangement, 

 while in the higher orders they are constant and cyclic. 



Pandanales. This is a very primitive order of about 450 species 

 grouped into 3 families. Many are hydrophytes. The screw pine (Pan- 

 danus) of the tropics is the representative form, but the most familiar 

 member in temperate regions is the cattail (Typha). The flower clusters 

 are usually surrounded, when young, by a conspicuous sheathing bract. 

 The flowers are imperfect and mostly naked, but sometimes a simple 

 bract-like perianth is present. The stamens and carpels show great varia- 

 tion in number and are mostly spiral. Both hypogyny and apocarpy are 

 features of the order. 



Helobiales. Here belong about 300 species of primitive aquatic and 

 marsh plants comprising 6 families. Familiar genera are Potamogeton, 

 Sagittaria, Elodea, and Alisma. The Helobiales are a genetic group, 

 showing several lines of descent. A sheathing bract surrounds the inflo- 

 rescence, as in the Pandanales, but the flowers are usually perfect. The 

 flowers may be naked, apetalous, or choripetalous, are usually hypogy- 



