400 PLANT MORPHOLOGY 



Urticales. This is an order of about 1,500 species distributed among 

 4 families: the Ulmaceae and Moraceae, which are mostly woody, and the 

 Cannabinaceae and Urticaceae, which are mostly herbaceous. Repre- 

 sentative members of the Ulmaceae are the elms {Ulmus); of the Mora- 

 ceae, the mulberries {Morns) and figs (Ficus); of the Cannabinaceae, 

 hemp {Cannabis) and hop {Hutnulus); of the Urticaceae, the nettles 

 {Urtica). The flowers are mostly imperfect, apetalous, hypogynous, and 

 syncarpous. The stamens equal the perianth segments in number. The 

 ovary is unilocular, usually having a single ovule. 



Santalales. These are parasitic herbs and woody plants, numbering 

 about 1,200 species, mostly tropical. The Loranthaceae and Santalaceae 

 are the largest of 8 families. The mistletoes belong to the Loranthaceae. 

 The flowers are perfect or imperfect and epigynous, mostly with a petaloid 

 perianth consisting of a single whorl but sometimes differentiated into a 

 calyx and corolla. The stamens equal the sepals in number. There are 

 generallj^ three united carpels, mostly forming a unilocular ovary. 



Aristolochiales. This is a small order of herbs and woody plants, the 

 principal family, the Aristolochiaceae, numbering about 200 species. 

 The chief genus is Aristolochia. The flowers are perfect and epigynous, 

 with a highly developed petaloid perianth consisting of a single whorl of 

 united parts. The ovary is multilocular and has an indefinite number of 

 ovules. 



Polygonales. This is a small order of 800 species of herbs and woody 

 plants, all belonging to the Polygonaceae. Representative genera are 

 smartweed {Polygonum), dock {Rumex), rhubarb {Rheum), and buck- 

 wheat {Fagopyrum). The small flowers, mostly borne in spikes, are per- 

 fect or sometimes imperfect, regular, hypogynous, and syncarpous. The 

 perianth, consisting of a single whorl, is bract-like. The unilocular ovary 

 contains a single ovule. 



The preceding orders, with some others of less importance, constitute 

 the apetalous series of the Archichlamydeae. They are characterized by 

 flowers that, with few exceptions, have a simple perianth which is not 

 differentiated into a distinct calyx and corolla but consists of a single 

 whorl of parts. Some members have naked flowers. Most of these 

 orders are of uncertain relationships. Some may be primitive, while 

 others are doubtless reduced. 



The following orders, constituting the choripetalous series of the Archi- 

 chlamydeae, typically have a perianth consisting of two distinct whorls — 

 calyx and corolla — the members of which are separate and distinct. 



Centre spermales. This assemblage is often broken up into two orders, 

 the Chenopodiales and Caryophyllales. It includes about 3,500 species 

 of herbs grouped into 10 families, of which 4 are of greatest interest, viz., 



