Part 3, 1908] ROSACEAE 253 
Leaves l-nerved ; petals spatulate or oblanceolate. 
Leaves spatulate, spreading ; racemes short, 14 cm. long; bracts usually 
shorter than the flowers. 
Leaves and sepals sparingly strigose, the latter acuminate; petals very 
acute or acuminate. 3. P. acuminatum, 
Leaves and sepals canescent, the latter acute; petals mostly obtuse. 4. P. caespitosum. 
Leaves narrowly oblanceolate, erect or ascending; inflorescence 4-10 cm. 
long, often branched ; bracts usually exceeding the flowers. 5. P. elatius. 
1. Petrophytum Hendersoni (Canby) Rydberg. 
Eriogynia Hendersoni Canby, Bot. Gaz. 16: 236. 1891. 
Luetkea Hendersoni Greene, Pittonia 2: 219. 1892. 
Spiraea Hendersoni Piper, Erythea 7: 172. 1899. 
A depressed cespitose undershrub ; season’s branches 14 cm. long, ascending; leaves 
spatulate, 1-2 cm. long, 4-6 mm. wide, thick, more or less distinctly 3-ribbed beneath, spar- 
ingly and finely appressed-hairy or glabrate ; peduncles 4-8 cm. long, sparingly silky, with 
few, bract-like linear leaves, 3-6 mm. long; pedicels 4-5 mm. long with a small linear- 
subulate bractlet at the middle; hypanthium hemispheric, less than 1 mm. deep, 10-nerved ; 
sepals 1.5 mm, long, oblong, obtuse; petals obovate or oval, 2.5 mm. long; disk crenulate 
on the edge, pubescent within; follicles about 2 mm. long, glabrate except the strigose 
ciliate upper suture. , 
TYPE LOCALITY: Vertical cliffs near the summit of the Olympic Mountains, Washington. 
DISTRIBUTION: Olympic Mountains, Washington. 
2. Petrophytum cinerascens (Piper) Rydberg. 
Spiraea cinerascens Piper, Erythea 7: 171. 1899. 
Luetkea cinerascens Heller, Muhlenbergia 1: 53. 1904. 
A densely cespitose undershrub, with short stout branches; season’s branches 1 cm. 
long or less; leaves 3-ribbed, oblanceolate, obtuse or acutish, 1-2.5 cm. long, thick and leath- 
ery, cinereous, pilose; blade contracted below into a short petiole; peduncles cinereous, 
5-15 cm. long, with narrowly linear-oblanceolate to subulate bractlike leaves, the larger 1 
cm. long; inflorescence often with a few branches; pedicels 1-4 mm. long, with linear-sub- 
ulate bractlets near the base; hypanthium hemispheric or somewhat turbinate, less than 1 
mm. deep; sepals lanceolate, acuminate, nearly 2 mm. long, cinereous; petals spatulate or 
oblanceolate, obtuse, about 2mm. long; stamens 15-25; follicles 4-7, sparsely pilose, 3 mm. 
long; seed usually solitary, acute at each end. 
TYPE LOCALITY: Bluffs of the Columbia River, Washington, twelve miles south of Chelan, in 
crevices of basaltic rock. ‘ 
DISTRIBUTION: Type locality and vicinity. 
3. Petrophytum acuminatum Rydberg, sp. nov. 
A densely cespitose undershrub ; season’s branches less than 1 cm. long; leaf-blades ob- 
lanceolate, 1-1.5 cm. long, 2-4 mm. wide, sparingly and finely pilose, 1-ribbed, thick, mu- 
cronate at the apex, contracted below into short petioles; peduncles 6-8 cm. high, sparingly 
pubescent, with a few subulate or narrowly linear-oblanceolate bract-like leaves ; pedicels 2-3 
mm. long; hypanthium somewhat turbinate, less than 1 mm. deep; sepals lanceolate, acu- 
minate, 1.5-2 mm. long; petals oblanceolate, acute or acuminate, 2-2.5 mm. long; fruit 
unknown. 
Type collected at Big Arroyo, Tulare County, California, in 1904, Culbertson [Baker's distri- 
bution no.] 4540. 
4. Petrophytum caespitosum (Nutt.) Rydb. Mem. N. Y. Bot. 
Gard. 1: 206. 1900. 
Spiraea caespitosa Nutt.; T. & G. Fl. N. Am. 1: 418. 1840. 
Eriogynia caespitosa S, Wats. Bot. Gaz. 15: 242, 1890. 
Luetkea caespitosa Kuntze, Rev. Gen. 217. 1891. 
A densely cespitose undershrub, forming large flat patches appressed to the rocks; 
season’s shoots very short; leaves spatulate, 5-12 mm. long, 2-4 mm. wide, densely silky, 
1-ribbed, obtuse or mucronate; peduncles 3-10 cm. high, silky, their leaves subulate, bract- 
