Physaria brassicoides Rydb. 

 Brassicaceae 

 Mustard twinpod 

 A. Description 



1. General description: Herbaceous perennial forming basal 

 rosettes, arising from a taproot. Leaves numerous, restricted 

 to base and silvery grey throughout. Bright yellow flowers in 

 raceme on multiple stems 5-15 cm (2-6 in) long. Fruits with 

 two inflated capsules, indented at the top and the bottom. 

 On 2 June 1994, most plants in one population were in early 

 fruit, with a few still in flower. On 11 June plants, were in 

 fruit, and on 2 July many fruits had dehisced. 



2. Technical description: Cespitose perennial, silvery- 

 stellate throughout, stellate with forked rays; stems several 

 to numerous, rather stout for the genus, simple, arising 

 laterally, 5-15 cm long including the fruiting racemes; Basal 

 leaves numerous, thick, scurfy above, repand or rarely entire, 

 206 cm long, 1-2.5 cm wide, blades orbicular to obovate, 

 petioles somewhat winged; cauline leaves few, oblanceolate to 

 broadly spathulate, , obtuse to subacute, entire, 1-2 cm long, 

 3-5 mm wide. Petals yellow, spatulate. Fruiting pedicels 

 divergent, straight or somewhat curved, 5-10 mm long. 

 Siligues didymous, erect, cordate, moderately inflated, 

 loosely but densely pubescent with spreading stellae, obtuse 

 or with an obscure sinus at base, apical sinus deep and broad, 

 valves 608 mm high. Replum linear-oblong, constricted, 3-4 mm 

 long, ca. 1 mm wide. Styles 4-5 mm long. Ovules 2 per locule 

 (Rollins 1993) . 



3. Diagnostic characteristics: The only other Physaria in 

 eastern Montana is P. didymocarpa , which superficially 

 resembles P. brassicoides . The fruit is needed to distinguish 

 the two species with certainty. The P. brassicoides has a 

 fruit with a cordate outline, indented only on the top, while 

 P. didymocarpa has a "didymous" (dumbbell) outline, with deep 

 sinuses (indentations) on both top and bottom of the silique. 

 In addition, P. brassicoides has two funiculi per locule (and 

 usually two seeds, but the funiculi are evident as small 

 "pegs" along the upper portion of the fruit partition) ; a 

 narrow, linear partition of the fruit (which can be observed 

 by ripping off half of the fruit) ; and the fruit itself, which 

 is more deeply indented above than below. Also, the hairs of 

 the basal leaves, under lOx magnification, are readily 

 apparent as stellae, with slightly ascending arms. Note: P. 

 didymocarpa Rydb. is not known from the South Dakota flora 

 (from Great Plains Flora Association 1986, Hitchcock et al . 

 1984) . 



47 



