412 



ROSACEAE 



or less 3-nerved beneath, sparingly appressed-pubescent or glabrate; peduncles 4-8 cm. long 

 with few bract-like linear leaves; racemes narrow, 2.5-5 cm. long, densely flowered; sepals 

 oblong, obtuse; petals 2.5 mm. long, obovate or oval. 



Rocky cliffs, Boreal Zones; Olympic Mountains, Washington. Type locality: vertical cliffs near the summit 

 of the Olympic Mountains. June— Sept. 



2. Petrophytum cinerascens (Piper) Rydb. Gray Rock-spiraea. Fig. 2370. 



Spiraea cinerascens Piper, Erythea 7: 171. 1899. 

 Luetkea cinerascens Heller, Muhlenbergia 1 : 53. 1904. 

 Petrophytum cinerascens Rydb. N. Amer. Fl. 22: 253. 1908. 



Densely cespitose undershrub with short, stout branches. Leaves oblanceolate, 1-2.5 cm. 

 long, 3-nerved, somewhat cinereous with a short appressed rather sparse pubescence; peduncle 

 cinereous, 5-15 cm. long; raceme often with a few branches below; sepals lanceolate, acuminate, 

 about 2 mm. long, short-pubescent and glandular ; petals narrowly oblong, scarcely 2 mm. 

 long and but little exceeding the sepals. 



Bluffs, along the Columbia River, Chelan County, Washington. Type locality: rocky bluffs along the 

 Columbia River, about twelve miles south of Chelan. June— Sept. 



3. Petrophytum caespitosum (Nutt.) Rydb. Cespitose Rock-spiraea. Fig. 2371. 



Spiraea caespitosa Nutt. ex Torr. & Gray, Fl. N. Amer. 1 : 418. 1840. 



Eriogynia caespitosa S. Wats. Bot. Gaz. 15: 242. 1890. 



Luetkea caespitosa Kuntze, Rev. Gen. PI. 217. 1891. 



Petrophytum caespitosum Rydb. Mem. N.Y. Bot. Gard. 1 : 206. 1900. 



Densely cespitose, forming low depressed mats. Leaves spatulate, 5-12 mm. long, 1- 



nerved, densely silky-pubescent; peduncles 3-10 cm. long, silky, with small bract-like subulate 



leaves ; raceme narrow, 1-4 cm. long, usually simple ; sepals ovate-lanceolate, acute ; petals 



spatulate or oblanceolate, 1 . 5 mm. long. 



On rock ledges, Boreal Zones; Montana and Black Hills, South Dakota, to California, Arizona, and New 

 Mexico. In California it occurs in the southern Sierra Nevada, Panamint, and Providence Mountains. Type 

 locality: on high shelving rocks, in the Rocky Mountains, towards the sources of the Platte. June— Sept. 



Petrophytum acuminatum Rydb. N. Amer. Fl. 22: 253. 1908. Closely related to P. caespitosum and 

 possibly only a form of it. Distinguished by the sparingly pilose leaves and peduncles, the lanceolate acuminate 

 sepals, and the oblanceolate, acute or acuminate petals. Known only from the type collection at Big Arroyo, 

 Tulare County, California. 



5. LUETKEA Bong. Mem. Acad. St.-Petersb. VI. 2: 130. 1832. 



Cespitose woody plants, with prostrate or decumbent stoloniferous branches. Leaves 

 twice or thrice ternately dissected. Flowers racemose, perfect. Hypanthium hemispheric; 

 sepals and petals 5 ; stamens about 20, their filaments subulate. Pistils usually 5, distinct ; 

 ovules several, pendulous. Follicles coriaceous, dehiscent on both sutures. [Name in 

 honor of Count F. P. Luetke, 1797-1882, commander of a Russian exploring expedition in 

 the Arctic] 



A monotypic genus of northwestern North America. 





2369 

 2369. Petrophytum Hendersonii 



2370 

 2370. Petrophytum cinerascens 



2371 

 2371. Petrophytum caespitosum 



