Reptans: Answers to key questions in Budd's Flora and Manual of Montana Vascular Plants leading to this species. 

	plants annual, lacking a branched caudex; NOT [plants obviously perennial, some plants with a branched caudex and flower stems from previous years]
	upper stem glabrous; NOT [upper stem pubescent]
	stem leaves all or mostly opposite; NOT [stem leaves alternate]
	inflorescence short, with stems flexuous; NOT [inflorescence elongate]
	raceme completely ebracteate; NOT [lowest pedicels subtended by bracts]
	flowers white; NOT [flowers yellow]
	pedicel shorter than mature fruit; NOT [lower pedicels much longer than mature fruit]
	fruits pubescent; NOT [fruits glabrous]

Draba: Answers to key questions in Budd's Flora and Manual of Montana Vascular Plants leading to this genus. 

	plants pubescent; NOT [plants glabrous]
	plants not with very large basal leaves; NOT [basal leaves 40 cm long or longer]
	siliques a few times longer than wide; NOT [siliques many times longer than wide (Boechera)]
	siliques flattened parallel to the septum, at least twice as wide as thick; NOT [siliques flattened at right angles to the septum], NOT [siliques round, oval, or 4-angled in cross-section], NOT [pods subglobose]
	silique not samara-like; NOT [silique oblong, wing-like, resembling a samara]
	silique beakless, often with a short style at the tip <=1 mm long; NOT [silique with a large, usually seedless (sometimes 1-seeded), beak-like, upper portion and a seed-bearing lower portion]
	silique rounded to pointed on top or obscurely indented; NOT [silique definitely indented or concave on the top]
	silique opening lengthwise; NOT [silique globular, remaining on seed], NOT [silique elongate, breaking in two at the narrowed middle]
	silique with >2 seeds per locule; NOT [silique with 1 to 2 seeds per locule]; NOT [silique 1-seeded]
	seeds in 2 rows in each locule (sometimes rows are imperfect); NOT [seeds in 1 row per locule]

Cruciferae: Answers to key questions in Budd's Flora  leading to this family. 

	herbs; NOT [shrubs or trees]
	plants terrestrial or semiaquatic; NOT [plants aquatic, leaves submerged or floating]
	plants not with colored milky juice
	plants with more than one normal leaf
	some or all leaves alternate; NOT [leaves opposite, whorled, or basal]
	leaves without stipules, or having glands; NOT [leaves with stipules]
	flowers with two floral rings
	calyx regular; NOT [calyx irregular, some sepals smaller than others]
	sepals 4
	corolla regular in shape; NOT [corolla irregular in shape]
	each petal distinct from the others
	petals 4
	stamens 6, four long and two short
	ovary superior; NOT [ovary inferior]
	carpels 1 or 2