MUSTARD FAMILY 99 



Style distinct, but short; blades of the petals broadly obovate, much ex- 

 ceeding the sepals. 15, L. idahoense. 

 Style none; blades of the petals spatulate. 



Pubescence, if any, of cylindrical or subulate hairs: petals well exceed- 

 ing the sepals, at least in the earlier flowers. 

 Stem glabrous or nearly so. 



Cotyledons ciccunibent; petals broadly spatulate. 



.16. L. virginicum. 

 Cotyledons incumbent; petals narrowly spatulate or oblance- 

 olate. 17. L. lexanum. 



Stem densely pubescent. 18. L. hirsuium. 



Pubescence of the stem of short, clavate hairs; petals about equalling 



Stem low, 1-3 dm. high, branched below; primary basal leaves 



oblanceolate, serrate. 19. L. ramosum. 



Stem taller, 4r-6 dm. high, simple below, branched above; primary 

 basal leaves pinnatifid. 20. L. simile. 



Petals none or minute, scarcely more than half as long as the sepals, linear or 

 linear-spatulate. 

 Plants branched near the base; petals usually present (except in L. diver- 

 gens) . 

 Racemes usually numerous, on short branches from the axils of the upper 

 leaves; pods broadest below the middle; wlng-ma,rglns narrow. 

 Axillary racemes very short and dense, usually shorter than the 

 leaves; petals more than half as long as the sepals. 



21. Z.. ramosissimum. 

 Axillary racemes at last elongate; petals very minute or lacking. 



22. L. divergens. 

 Racemes elongate, terminal; pods broadest above the middle; wing- 

 margins fuHy 0.5 mm. wide at the apex. 23. L. elongatum. 



Plant simple below, branched above; petals none; racemes elongate, 

 terminal. 24. L. densiflorum. 



Pods hirsute, at least on the margins. 



Stem-leaves Unear, mostly entire. 25. L. pubecarpum. 



Stem-leaves spatulate, toothed or lacimate. 26. L. Georginum. 



Wing-margins of the fruit produced at the apex into acute lobes or teeth. 



Stem erect, 3-5 dm. high. 27. L. Fletcheri. 



Stem decumbent, 3-15 cm. high. 



Pod obovate or elliptic; stamens 2; leaves linear or linear-spatulate. 



28. X. Bourgeauanum. 

 Pod ovate; stamens 4; basal leaves often pinnatifid. 29. L. dictyotum. 



4. THLASPI (Tourn.) L. Penny Cress, Penny-grass. Wild Sweet 

 Alyssum. 



Pods orbicular in outline, broadly wing-margined and deeply notched at the apex; sepals 



green; annuals. 1. T. arvense. 



Pods obovate or oblauceolate-cuueate in outline, with narrow margins, acute, truncate 

 or slightly notched at the apex; sepals with white or rarely purplish margias; 

 perennials. 

 Petals 2.5-3 mm. long; pod oblanceolate-cuneate, 2-2.5 mm. wide. 2. T. parviflorum. 

 Petals 4-7 mm. long ; pods cuneate or obovate-cuneate, 3 mm. or more wide. 



Pods acutlsh at the apex, neither emarginate nor retuse. 3. T. californicum. 



Pods rounded or truncate at the apex, emarginate or retuse. 

 Pods rounded at the apex; sinus narrow. 



Caudex rather slender; stem 1-2 dm. high; petals spatulate, about 5 mm. 



long. 4. T. Nuttallii. 



Caudex stout, densely cespitose; stem less than 1 dm. high; petals broadly 

 obovate, 6-7 mm. long. 5. T. coloradense. 



Pods truncate or nearly so at the apex; sinus very broad and open. 



Stem 2—3 dm. high; stem-leaves ample, broader than the basal ones; sepals 



green, with white margins. 6. T. glaucum. 



Stem 1 dm. or less; stem-leaves reduced; sepals and often also petals 

 pxu'plish. 7. T. purpurascens . 



6. BURSA Weber. Shepherd's Purse. l. B. Bursa-pastoris. 



6. HUTCHINSIA R. Br. l. H. procumbens. 



7. SMELOWSKIA C. A. Meyer. 



Basal leaves merely lobed, cuneate to oblanceolate in outline; pod 5-6 mm. long, tapering 



towards the base. 1. S. lobaia. 



Leaves all deeply pinnatifld. 



Pod ovate, 4-5 mm. long, obtuse at the base; calyces and pedicels densely villous; 



leaves whlte-villous. 2. S. ovalis. 



Pod l2uiceolate or oblanceolate, 7—12 mm. long, tapering at each end. 



Segments of the basal leaves spatulate or oblong. 3. S. americana. 



Segments of the basal leaves luiear or linear-oblong. 4. S. lineariloba. 



8. DITHYREA Harv. l. D. Wislizeni. 



