356 URTICACEAE 



of as many stamens as there are sepals. Gynoecium of a single carpel or 2 

 united carpels. Fruit an achene, samara, drupe or syncarp. Endosperm usu- 

 ally scant or wanting. 



Fruit an achene, the achenes sometimes in the accrescent sepals and disposed in a syncarp. 



Flowers not on a receptacle : fruits not forming syncarps : sepals neither thick and juicy, nor envel- 

 oping the achenes. 

 Style or stigma 1, the latter sometimes tufted : ovule erect ; filaments inflexed in the bud. 



Fam. 1. URTICACEAE. 



Styles or stigmas 2 : ovule pendulous : filaments erect in the bud. Fam. 2. Cannabinaceae. 

 Flowers on the outside or inside of a receptacle : fruits forming syncarps : 



sepals accrescent, enveloping the achenes. Fam. 3. Artocarpaceae. 



Fruit a samara or a drupe, sometimes nut-like. Fam. 4. Ulmaceae. 



Family 1. URTICACEAE Reichenb. Nettle Family. 



Herbs (or in the tropies, shrubs or trees), with pellucid and watery, or firm 

 tissues, sometimes armed with stinging hairs. Leaves alternate or opposite : 

 blades simple, entire, toothed or rarely lobed : stipules usually present. Flow- 

 ers small, greenish, dioecious, monoecious or polygamous, in axillary, simple or 

 compound, often congested cymes. Calyx of 2-5 distinct or partially united 

 equal or unequal sepals. Androecium of 2-5 stamens inserted at the base of 

 the sepals or calyx lobes, reduced to staminodia in the pistillate flowers, or none. 

 Filaments distinct, strongly inflexed in the bud. Anthers opening lengthwise. 

 Gynoecium a single carpel. Ovary superior, 1-celled. Style or stigma solitarj', 

 terminal or becoming lateral, the stigma often tufted. Ovule erect or nearly so, 

 orthotropous or half-amphitropous. Fruit an achene. Endosperm oily, some- 

 times nearly wanting. Embryo straight, with broad cotyledons. 



Plants armed with stinging hairs. 



Leaves opposite : staminate flowers with 4 sepals and 4 stamens : achenes equilateral : style terminal. 



1. Urtica. 

 Leaves alternate : staminate flowers with 5 sepals and 5 stamens : achene oblique : 



style lateral. 2. Urticastrum. 



Plants glabrous or at least destitute of stinging hairs. 

 I, I Flower-clusters not involucrate : leaves mostly opposite. 



Flower-clusters in axillary often clustered cymes : achene not included. 3. Adicea. 



Flower-clusters spicate on slender mostly simple branches : achene included. 4. Boehmeria. 

 Flower-clusters involucrate : leaves alternate. 5. Parietaria. 



1. URTICA L. 



Annual or perennial often coarse lierbs armed with stinging hairs. Leaves opposite : 

 blades membranous, toothed or incised-Iobed, mostlj' 5-7-nerved : stipules free. Flowers 

 dioecious or monoecious, in axillary cymes wliich are panicled, or often much reduced, 

 the staminate with 4 nearly distinct sepals, which are concave or hooded at the apex, 4 

 stamens and a rudimentary ovary. Pistillate flowers with a perianth of 4 nearly distinct 

 sepals, two of them larger than those of the other pair, and an equilateral ovary : stigma 

 tufted. Achene flattened, with a membranous or crustaceous pericarp, enveloped in the 2 

 accrescent sepals. Seed with its membranous testa and pericarp often adherent. Nettle. 



Annual : flower-clusters simple. 



Leaf-blades incised-toothed, the upper ones but little reduced. 1. U. urens. 



Leaf-blades crenate-dentate, the upper ones much reduced. 2. U. chamaedryoides. 



Perennial : flower-clusters compound. 

 Stems sparingly bristly. 



Leaf-blades with coarse flaring teeth : sepals oval. 3. U. Breiven. 



Leaf-blades with rather fine ascending or incurved teeth : sepals orbicular. 4. V. gracilis. 

 Stems densely bristly. 5. U. dioica. 



1. Urtica urens L. Annual, stoutish. Stems erect or ascending, 1-4 dm. tall, simple 

 or branched, bristly with stinging hairs : leaf-blades thin, oval or ovate, 1-4 cm. long, 

 acute, glabrous or sparingly bristly, acute or truncate at the base, incised, the tooth-like 

 segments ascending or spreading, entire or toothed ; petioles slender, h as long as the 

 blades or much longer : flower-clusters shorter than the petioles or a little longer : sepals 

 oval or broadly oblong, less than 1 mm. long : achene ovoid, nearly 2 mm. long, enveloped 

 in the accrescent sepals. 



In waste places, Newfoundland to New York and Florida. Also in California. Naturalized from 

 Europe. Spring to fall. 



2. Urtica chamaedryoides Pursh. Annual, slender. Stems solitary or tufted, as- 

 cending, weak, 1-10 dm. tall, sparingly armed with stinging bristle-like hairs other- 



