42 



TECHNICAL DESCRIPTION: Decumbent to prostrate, much- 

 branched perennial from rhizomes, 1-4 dm (4-16 in) tall, 

 moderately to densely hirsute with slender, elongate 

 trichomes. Leaves sessile, blades oblong to oblanceolate in 

 outline, 2.5-5 cm (1-2 in) long, 0.5-1 cm (.2-. 4 in) wide, 

 hirsute on both surfaces especially at the midrib, acute to 

 obtuse, shallowly to deeply sinuate, auriculate and partly 

 clasping at the base. Racemes are terminal and axillary, 

 all about the same age or the lowest ones with the oldest 

 siliques. Sepals are yellowish-green, 2.1-3.1 mm (.08-. 12 

 in) long, persistent with fruit. Petals are bright yellow 

 2-3.7 mm (.08-. 15 in) long, to 1 mm (.04 in) longer than the 

 sepals. Silques are globose to subglobose, 2.3-3.4 mm (.09- 

 .13 in) long, 1.2-2.3 mm (.05-. 09 in) wide, ca. 1.3-2X 

 longer than wide, densely strigose on the valves; pedicels 

 strongly recurved, sometimes giving the raceme a 1-sided 

 appearance, 3.5-6.5 mm (.14-. 26 in) long (Larson 1993). 



LOCAL FIELD CHARACTERS: The yellowcress genus ( Rorippa ) is 

 distinguished in having simple hairs, small flowers (petals 

 less than 0.6 mm, i.e. 0.2 in), and lobed leaves. It most 

 closely resembles winter cress ( Barbarea orthoceras ) , but 

 persistent sepal yellowcress is a rhizomatous perennial 

 while winter cress is biennial. 



There are four other species of yellowcress in central and 

 eastern Montana. Three of the four are short-lived compared 

 to persistentsepal yellowcress; being annual, biennial or 

 short-lived perennial and lacking rhizomes. The only 

 perennial is Rorippa sinuata , which has elongate, glabrous 

 siliques compared to those of persistentsepal yellowcress 

 which are 1-2.5 times as long as wide and hairy with hairs 

 that are broadened at based and pointed at tip (from Dorn 

 1984) . 



GEOGRAPHICAL DISTRIBUTION 



1. RANGE: Persistentsepal yellowcress is a regional endemic 



known from Wyoming, northwestern Nebraska, North Dakota and 

 Montana (Cascade, Choteau, Custer, McCone, and possible 

 Yellowstone counties) . In addition, there is a remote 

 outlying popualtion in the Northwest Territories which is 

 likely to have been carried by waterfowl (Rollins 1993). 

 Note: In addition, four specimens at Montana State 

 University (MONT) originally identified as Rorippa calycina 

 have been reviewed and presumed annotated to other species 

 in the genus. Some of these had been included in the 

 summary of species status by Watson (1976), reviewed by and 

 discussed in Lichvar (1981). 



