FLORA OF THE DISTRICT OF COLUMBIA. 



267 



9. HIERACItJM L. 



Leaves acute or acuminate, glabrous, glaucous beneath; heads small, 12-20-flowered, 



on long slender stalks, loosely panicled 1. H. pamculatum. 



Leaves obtuse or rounded at the apex, copiously hairy; heads larger, the flowers 

 usually 20-50. 

 Stems hairy throughout, bearing numerous leaves, without a basal tuft of leaves at 

 flowering time; heads in narrow panicles or corymbs. 

 Inflorescence leafy-bracted, the heads on very stout stalks, 40-50-flowered. 



2. H. scabrum. 



Inflorescence not leafy-bracted, the heads on comparatively slender stalks, 15-20- 



flowered 3. H. gronovii 



Stems glabrous except sometimes at the base, bearing only one or two leaves, with 

 a rosette of basal leaves at flowering time, these usually veined or mottled with 

 purple; heads in open panicles, on very slender stalks 4. H. venosum. 



1. Hieracium paniculatum L. 



Woods about Washington. Aug.-Oct. Eastern N. Amer. 



2. Hieracium scabrum Michx. Rough hawkweed. 

 Dry woods; common. Aug.-Oct. Eastern N. Amer. 



3. Hieracium gronovii L. Hairy hawkweed. 

 Dry woods and open fields; common. Aug.-Oct. Eastern U. S. 



4. Hieracium venosum L. Rattlesnake-weed. 

 Dry woods; abundant. Apr.-Sept. Eastern IT. S. (Including II. venosum sub- 



caulescens of Ward's Flora.) ^ 



Crepis pulchra L. was found in waste ground near the Washington Monument in 1898 

 and 1890. Native of Eur. C. capillars (L.) Walk. (C. www L.), also a European 

 species, was collected in the Department of Agriculture grounds as early as 1872 and 

 as late as 1894, but is not established in our region. 



152. AMBROSIACEAE. Ragweed Family. 



Fruit covered with very numerous long, usually hooked spines; leaves alternate. 



1. XANTHITJM. 



Fruit bearing usually 4-8 short tubercles; leaves all or only the lower ones opposite. 



2. AMBB.OSIA. 



1, XANTHITJM L. Cocklebur. 

 Stems armed in the axils with branched spines; leaves lanceolate, white beneath; 



fruit with one short beak or beakless 1- x - spinosum. 



Stems without spines; leaves broadly ovate or broader, green on both sides; fruit 

 with 2 long beaks at the apex. 

 Bodv and prickles of the fruit glabrous or puberulent, the beak? straight or nearly so. 



2. X. americanum. 



Body and prickles of the fruit hairy, the beaks incurved 3. X. commune. 



1. Xanthium spinosum L. Spiny cocklebur. 

 Occasional in waste ground about Washington and Alexandria, Aug.-Oct. In ative 



of Eurasia; adventive in N. Amer. 



2. Xanthium americanum Mill. 



Waste or cultivated ground or alluvial flats. Aug.-Oct. Eastern N. Amer. (A. 



canadense of Gray's Manual; X. glabratum Britton.) 



3. Xanthium commune Britton. 



Alluvial soil along the Potomac and its larger tributaries. Aug.-Oct. Widely dis- 

 tributed in N. Amer. 



