Rosaceae 209 
DD. Twigs glabrous. E. (S. idahoensis. ) 
S. roseata, Rydb. 
CC. Under side of leaves tomentose. W. 
S. douglasii Hook. (Hard-hack) 
AA. Flowers white. 
E. Infloresence flat-topped. W.C. E. (S. lucida. ) 
S. corymbosa Raf. (Flat White Spiraea) 
EE. Inflorescence not flat-topped. 
F. Lower leaf-surface tomentose. C. 
S. tomentulosa Rydb. 
FF. Lower leaf-surface not tomentose. C. F. 
S. pyramidata Gr. (Pyramid-bush) 
PETROPHYTUM (Petrophyton) 
Shrubs, low, prostrate, caespitose, on rocks. Leaves oblanceolate or spatulate, 
entire, coriaceous, evergreen, crowded on the short branches. Flowers perfect, in ra- 
cemes; racemes rarely compound. Calyx-tube hemispheric; segments 5. Petals white. 
Stamens about 20. Receptacle-disk entire-margined.  Pistils 3—5; ovary and lower 
part of style very hairy; style terminal. Follicles leathery. Seeds 2—4, linear. (Gk. 
petros—a stone, phyton—=a plant; referring to their rock habitat. ) 
A. Leaves 3-veined. 
B. Sepals obtuse; petals obovate or oval; leaves glabrous or nearly so. W. (Luet- 
kea hendersoni; Spiraea hendersoni.) 
P. hendersoni Rydb. 
BB. Sepals acuminate; petals spatulate or oblanceolate; leaves canescent. E. (Spi- 
raea cinerascens. ) P. cinerascens Rydb. 
AA. Leaves I-veined. C. E. (Spiraea caespitosa.) 
P. caespitosum Rydb. 
LUTKEA PARTRIDGE-FOOT 
Shrubs, small, caespitose, decumbent or creeping. Leaves 2—3-ternately dissected, 
grooved above. Flowers perfect, in a raceme. Calyx-tube hemispheric; segments 5. 
Petals white. Stamens about 20. Receptacle-disk about 10-lobed. Pistils 4—6, dis- 
tinct; styles terminal, deciduous. Follicles coriaceous. Seeds several, linear-lanceolate, 
acute at both ends. (Honor of F. P. Lutke, a Russan explorer.) W.C. (L. sibbal- 
dioides. ) L. pectinata Kuntze 
ARUNCUS GOAT’S BEARD 
Herbs, perennial, with thick rhizomes. Leaves 2—3 times ternately- or pinnately- 
dissected; stipules none. Flowers dioicous, in a large panicle with spike-like branches. 
Calyx-cup of staminate flowers flat or saucer-shaped, 5-angled; segments 3-angled; petals 
white; stamens 15—-30; receptacle-disk 5-lobed: pistils' 3-5, rudimentary; styles none. 
Pistillate flowers much smaller than the staminate: stamens rudimentary; pistils 35, dis- 
tinct; styles obliquely terminal. Follicles oblong, cartilaginous. Seeds 6—12, attenuate 
at both ends. (L. aruncus—the beard of a goat; probably suggested by the long white 
spikes of flowers.) W.C. E. (A. vulgaris; A. sylvester; A. acuminatus.) 
A. aruncus Karst. 
