Nelson : New Plants from Wyoming 265 



rous inflorescence separate it, as do also ^the veiy numerous and 

 slender branches of the caudex. D. saximontana, in many re- 

 spects, is nearer to D. oligosperma Hook, but it seems to be sepe- 

 rated from the original arctic form of that by easily recognized 

 characters. First, it is to be noted that that had white flowers, a 

 fact stated not only in the original description (Hook Fl. Bor. Am. 

 1:51) but in an added note. D. oligosperma, I. c, is compared to 

 D. hirta L. as a petal and habit which is further evidence that that 

 is very different from this plant. D. oligospermia also seems to 

 have had a lobed (" sub-triplo ") stigma and more numerous 

 seeds. 



■ 



D. saximontana is abundant in a few of the foothill slopes of 

 the Laramie Plains, mostly on stony ledges that are partly sand- 

 covered. Collected a number of times but no. 4323 may be cited 



as type. 



Thlaspi parviflorum 



Biennial or possibly more enduring, with a simple, vertical 

 tap-root, glabrous throughout, 1-2 dm. high : stems few to sev- 

 eral from the crown, simple, ascending or erect : crown leaves 

 small, 5-10 mm. long, rather numerous, elliptic to oval, short - 

 petioled : stem leaves 5—10, oblong, obtuse or sub-acute, sagittate- 

 clasping, the sinus shallow : raceme simple (rarely a branch or two 

 from the upper leaf axils : pedicels widely divaricate, scarcely 

 longer than the capsule : sepals ovate, mostly obtuse, greenish 

 with a white margin and purplish spot near the tip : petals white, 

 spatulate, 2—3 mm. long, about twice as long as the sepals : cap- 

 sule spatulate, in dried specimens often appearing unequilateral, 

 barely emarginate, 5—7 mm. long, 8-io-seeded, only slightly flat- 

 tened, not winged but rather strongly margined : style thick, only 

 about .5 mm. long. 



This is a peculiarly distinct species, and one not readily con- 

 founded with any of the numerous forms usually referred to T, 

 alpestre L. The small flowers and rather slender tap-root and the 

 narrow capsule will easily distinguish it even without reference to 

 the shape of the floral parts. Seemingly abundant on open slopes 

 in the northwestern part of Yellowstone Park. Glen Creek, June 

 28, 1899, no. 5554. 



J Potentilla virgulata 



Root thick and subfleshy, its one or two crowns scaly : stems 1 

 only from each crown, simple, erect, 3-4 dm. high, lightly pubes- 



