LACTUCA LEPTILUM 283 



white or brown hair-like bristles; receptacle flat, without chaff, involucre 

 cylindric, the bracts in several rows ; heads in panicles ; leaves alternate, 

 entire to pinnatifid ; annual, biennial or perennial. 



1. Pappus white; achenes with a distinct beak 



a. Flowers yellow or reddish-yellow 



(1) Leaves with spiny margins and often with 



spiny mid-ribs 



(a) Heads 6-12-flowered ; involucre 8-12 



mm. high L. scariola 



(b) Heads 12-many-flowered ; involucre 15- 



20 mm. high L. ludovicidna 



(2) Leaves without spiny margins or mid-rib; 



involucre 8-12 mm. high L. canadensis 



b. Flowers blue, purplish or white 



(1) Involucre 12-14 mm. high; achenes 1-3- 



nerved L. graminifolia 



(2) Involucre 16-18 mm. high; achenes striate L. pulchella 



2. Pappus brown ; achenes beakless ; flowers blue to 



yellowish or whitish L. spicdta 



LAYIA Hooker and Arnott 1833 

 (Named for Lay, a British naturalist) 



Heads with white or rose-colored rays, disk-flowers yellow, perfect, 

 achenes flattened, ray-achenes without pappus, disk-achenes with a pappus 

 of 10-20 bristles; receptacle flat, with chaff, involucre with flattened bracts, 

 enclosing the ray-achenes ; heads mostly solitary on the ends of branches ; 

 leaves alternate, usually pinnatifid ; annual. 

 Stems 8-15 in. high, much-branched; leaves lanceo- 

 late to linear, the lower pinnatifid; rays 8-13, 3- 

 lobed L. glandulosa 



LEPTILUM Rafinesque 1818 HORSEWEED 

 (Gr, leptos, narrow, from the small heads) 



Heads with white or purplish pistillate ray-flowers, disk-flowers per- 

 fect, yellow or yellowish, achenes flattened, oblong; receptacle flat, without 

 chaff, involucre bell-shaped, the bracts in 2-3 rows ; heads in racemes or 

 branched panicles; leaves alternate, simple; annual or biennial. 



1. Stems 1-6 ft. high; involucre smooth; rays white L. canadense 



2. Stems 3-12 in. high ; involucre hairy ; rays purp- 



lish L. divaricdtum 



