246 CONTRIBUTIONS FROM THE NATIONAL HERBARIUM. 



23. LYCOPUS L. 



Flower whorls bristly with long slender calyx teeth. 

 Leaves incised or pinnately lobed, at least at the base; corolla about, as long as the 



calyx 1. L. americanus. 



Leaves serrate ; corolla twice as long as the calyx 2. L. rubellus. 



Flower whorls not bristly, the calyx teeth short and inconspicuous. 

 Leaves mostly petioled, dark green, firm; root slender, not tuberous-thickened. 



3. L. virginicus. 

 Leaves mostly sessile, light green, thin; root tuberous-thickened. .4. L. uniflorus. 



1. Lycopus americanus Muhl. Water .horehound. 

 Wet soil; along the upper Potomac. June-Oct. Widely distributed in N. Amer. 



(L. sinuatus Ell.) 



2. Lycopus rubellus Moench. 



Wet soil along the Potomac and some of its tributaries; rarely collected. Aug.- 

 Oct. Eastern U. S. (L. europaeus intcgrifolius A. Gray.) 



3. Lycopus virginicus L. Btjglewort. 

 Common in swamps and low wet woods throughout our region. Aug.-Oct. Eastern 



U. S. (L. sherardi Steele.) 



4. Lycopus uniflorus Michx. 



Rarely collected; found in much the same habitats as the preceding species, chiefly 

 in the Coastal Plain. Eastern N. Amer. 



24. MENTHA L. 



Flowers in terminal leafless spikes. 



Spikes narrow, interrupted; leaves mostly sessile 1. M. spicata. 



Spikes thick, but slightly interrupted; leaves mostly petioled 2. M. piperita. 



Flowers in axillary whorls. 



Upper leaves much reduced in size 3. M. cardiaca. 



Upper leaves but slightly reduced 4. M. canadensis. 



1. Mentha spicata L. Spearmint. 

 Wet places throughout our region. July-Aug. Native of Eur.; widely natural- 

 zed in N. Amer. (M. viridis L.) 



2. Mentha piperita L. Peppermint. 

 Along the Potomac and its tributaries. July-Aug. Native of Eur.; naturalized in 



eastern N. Amer. 



3. Mentha cardiaca Baker. 



Shores of the Potomac; has been collected rarely. Northeastern N. Amer. 

 Variable in pubescence. Calyx teeth long-subulate. 



4. Mentha canadensis L. Wild mint. 

 Common along brooks and in moist places throughout our region. July-Oct. 



Widely distributed in N. Amer. 



25. COLLINSONIA L. 



1. Collinsonia canadensis L. Citronella. 



Frequent in dry woods of the Piedmont Region. Aug.-Oct. Eastern N. Amer. 



The style twisted to one side of the stamens gives the flowers a peculiar lop-sided 

 appearance. 



26. FERILLA L. 



1. Perilla frutescens (L.) Britton. Perilla. 



Not rare throughout our region, usually in waste places. July-Oct. Native of 

 Asia; naturalized in the eastern U. S. (P. otimoides erispa of Ward's Flora, ) 



