MUSTARD FAMILY 267 



2. Sisymbrium altissimum (L.) Britt. Tumble Mustard. Fig. 1996. 



Sisymbrium altissimum L. Sp. PI. 659. 1753. 



Norta altissima Britt. in Britt. & Brown, 111. Fl. ed. 2. 2: 174. 1913. 



Stems erect, widely branching, 6-12 dm. high, glabrous or nearly so. Lower leaves petioled, 

 runcinate-pinnatifid, the lobes lanceolate, often auriculate ; the upper smaller, often nearly sessile, 

 deeply pinnatifid into narrowly linear divisions ; pedicels thick, spreading, 6-8 mm. long ; petals 

 6-8 mm. long ; siliques very narrowly linear, stiff, 7-10 cm. long, 1 mm. thick, divergent ; valves 

 prominently 1 -ribbed. 



In waste places, naturalized from Europe; Washington to southern California. Becoming a troublesome 

 weed in eastern Washington and Oregon where it is locally known as Jim Hill Mustard. May-July. 



3. Sisymbrium orientale L. Oriental Sisymbrium. Fig. 1997. 



Sisymbrium orientale L. Cent. PI. 2: 24. 1756; Amoen. Acad. 4: 322. 1759. 



Erect annual herb, the stems branched with ascending branches, 2-5 dm. high, t hirsute- 

 pubescent. Leaves pinnate or the upper pinnatifid, petioled, 2-5 cm. long, the terminal lobe 

 hastate, linear-lanceolate to ovate, lateral lobes or leaflets 1-3 pairs, or on the upper leaves 

 absent ; sepals 4 mm. long ; petals 6, yellow ; fruiting racemes 8-20 cm. long ; pedicels 3-10 mm. 

 long, stout ; pods ascending, 4-6 cm. long, 1-1 . 5 mm. wide, straight, glabrous or nearly so. 



Native of the Old World, becoming well established in coastal California; San Francisco, Monterey, and 

 San Diego Counties. May. 



4. Sisymbrium irio L. Desert Mustard. Fig. 1998. 



Sisymbrium Irio L. Sp. PI. 659. 1753. 



Norta Irio Britt. in Britt. & Brown, 111. Fl. 2: 174. 1913. 



Annual herbs with erect stems 1-6 dm. high, mostly branching above the base, glabrous 

 throughout except for occasional villous hairs. Lower and upper leaves petioled, runcinately 

 2-4-parted with the terminal lobe larger than the lateral ones; inflorescence many-flowered, 

 flowers cream-colored; pedicels slender, spreading, 5-7 mm. long; siliques ascending, narrowly 

 linear, flexible, 2-3.5 cm. long, less than 1 mm. wide. 



Introduced weed, central southern California eastward through the desert area into Arizona and Sonora, 

 Mexico. Type locality: European. Feb.-April. 



15. ARABIDOPSIS (DC.) Schur. Enum. PI. Trans. 55. 1866. 



Annual or perennial herbs, with erect slender stems, pubescence of forked hairs. 

 Leaves simple, entire or toothed. Flowers small, white or pink, in terminal racemes. 

 Style very short ; stigma 2-lobed. Pod terete ; valves rounded, faintly nerved or nerve- 

 less, dehiscent. Seeds in 1 row in each cell, or in some European species in 2 rows; 

 cotyledons incumbent. [Name from the resemblance of this genus to Arabis.'] 



About 12 species, natives of the northern hemisphere. Type species, Arabis Thaliana L. 



1. Arabidopsis Thaliana (L.) Britt. Mouse-ear, Thale-cress. Fig. 1999. 



Arabis Thaliana L. Sp. PI. 665. 1753. 



Sisymbrium Thalianum A. Gray, Ann. Sci. Nat. 7: 399. 1826. 



Arabidopsis Thaliana Britt. in Britt. & Brown, 111. Fl. ed. 2. 2: 176. 1913. 



Annual, stem slender, erect, 5-40 cm. high, branching, more or less pubescent with short 

 stiff hairs. Basal leaves oblanceolate or oblong, narrowed to a petiole, entire or slightly toothed ; 

 upper leaves smaller, sessile ; pedicels slender, spreading, 4-8 mm. long ; flowers usually white, 

 3-4 mm. long, pods ascending, 10-15 mm. long. 



Waste places, especially in dry ground, Oregon and Washington, naturalized from Europe. May-July. 



16. HALIMOLOBUS Tausch, Flora 19: 410. 1836. 



Biennial or perennial herbs, with erect stems, mostly pubescent with forked hairs. 

 Basal leaves oblong, short-petiolate, the cauline amplexicaul or sessile and cuneate, usu- 

 ally toothed. Racemes leafless. Sepals erect, oblong, the interior pair saccate at base. 

 Petals white or yellow, spatulate. Stamens 6, with filiform filaments. Ovary broadly 

 cylindric ; ovules 8 to many ; style short, slender ; stigma minute, depressed. Silique terete, 

 on slender pedicels; valves 1-nerved. Seeds in 2 rows, minute and usually numerous. 

 [Name Greek, meaning jumping and silique, applied to these plants on account of their 

 resemblance to Alyssum halimifolium Willd.] 



An American genus of 11 known species. Type species, Halimolobus lasiolobus (Link) O. E. Schulz. 



1. Halimolobus diffusus (A. Gray) O. E. Schulz. Diffuse Halimolobus. 



Fig. 2000. 



Sisymbrium diffusum A. Gray, PI. Wright. 1: 8. 1852. 

 Hesperis diffusa Kuntze, Rev. Gen. PI. 2: 934. 1891. 

 Halimolobus diffusus O. E. Schulz, Pfianzenreich 4 105 : 285. 1924. 

 Sisymbrium diffusum var. Jaegeri Munz, Bull. S. Calif. Acad. 31: 61. 1932. 



Perennial with a short woody caudex, the flowering stems several, branching from the base, 



