266 CONTRIBUTIONS FROM THE NATIONAL HERBARIUM. 



8. LACTTTCA L. Lettuce. 



Achenes rounded at the apex or narrowed into a short stout beak; flowers blue or 

 white. 

 Pappus brown. Achenes with a very short beak; leaves usually deeply lobed. 



_ 1. L. spicata. 



Fappus white. 



Achenes distinctly beaked; leaves deeply lobed 2. L. floridana. 



Achenes not beaked; leaves merely toothed 3. L. villosa. 



Achenes tapering or abruptly contracted to a slender, usually long beak; flowers 

 usually yellow, sometimes blue. 

 Teeth of the leaves spine-tipped. Flowers yellow, 6-12 in each head. 



Leaves deeply lobed 4. L. scariola. 



Leaves finely toothed 5. L. virosa. 



Teeth of the leaves not spine-tipped. 

 Leaves hairy or bristly on the veins beneath; flowers blue or purplish. 



Stems long-hairy throughout; leaves merely toothed 6. L. steelei. 



Stems glabrous above; leaves nearly all deeply.lobed 7. L. hirsuta. 



Leaves glabrous; flowers yellow. 



Leaves entire or lobed, not clasping at the base 8. L. canadensis. 



Leaves entire or finely toothed, clasping at the base 9. L. sagittifolia. 



1. Lactuca spicata (Lam.) Hitchc. Blue lettuce. 

 Woods; Plummers Island and Terra Cotta. Aug. Eastern N. Amer., west to 



Colo. (Mulgedium spiadum DC.) 



The flowers are usually blue, but in a specimen from Plummers Island (Kearney 

 133) they are cream-colored. 



Lactuca spicata integrifolia (A. Gray) Britton is a form in which most of the leaves 

 are merely dentate; in the typical form they are usually deeply lobed. The sub- 

 species has been collected near Langley and St. Elmo. 



2. Lactuca floridana (L.) Gaertn. Florida lettuce. 

 Woods or open fields; common. Aug.-Sept. Eastern U. S. (Mulgedium flori- 



danum DC.) 



3. Lactuca villosa Jacq . 



Woods; frequent, Aug.-Sept. Eastern U. S. (Mulgedium acuminatum DC.) 



4. Lactuca scariola L. Prickly lettuce. 

 Waste ground; occasional; apparently a recent introduction. Native of Eur.; 



frequently adventive in the IT. S., but much less common than the next. 



5. Lactuca virosa L. Prickly lettuce. 

 Waste ground about Washington. May-Aug. Native of Eur. ; widely naturalized 



in the U. S., and often a pernicious weed. (L. scariola integrata Gren. & Godr.) 



6. Lactuca steelei Britton. 



The type was collected at Chevy Chase, Maryland, July 22, 1897 (Steele); found 

 also at Anacostia and Falls Church. Britton reports the species, doubtfully, from 

 Del. 



7. Lactuca hirsuta Muhl. 



Moist woods and thickets; frequent. July-Aug. Eastern N. Amer. 



8. Lactuca canadensis L. 



Woods and thickets; frequent. June-Aug. Widely distributed in N. Amer. 



9. Lactuca sagittifolia Ell. 



Woods; occasional. July-Sept. Eastern N. Amer., west to Idaho. (L. intcqri folia 

 Bigel.) 



