252 NORTH AMERICAN FLORA [VorumE 22 
TYPE LOCALITY: Northwest coast of America, about the Columbia. 
DISTRIBUTION : Lowlands, from British Columbia to California. 
ILLUSTRATIONS: Paxton’s Mag. Bot. 12: pi. 195, Ann. Soc. Agr. Bot. Gand 1: #1. 40; FI. 
Serres 2: f1.3; Cycl. Am. Hort. /. 2369. 
21. Spiraea subcanescens Rydberg, sp. nov. 
A low shrub; bark of twigs finely tomentose, brown; petioles 1-2 mm. long; leaf- 
blades lanceolate, 3-6 cm. long, about 1.5 cm. wide, firm, dark-green and slightly hairy 
above, tomentulose beneath, strongly veined, sharply and finely serrate throughout, acute 
at both ends; inflorescence rather small, dense, narrow, 5-10 cm. long, 1.5-2.5 cm. thick ; 
hypanthium densely pubescent, hemispheric, less than 1 mm. deep; sepals triangular- 
ovate, acute, reflexed in fruit; petals pink, nearly orbicular, 1.5 mm. long; follicles about 
2mm. long, glabrous. Perhaps a hybrid between S. somentosa and S. alba. 
Type collected near Anderson, South Carolina, in 1885, Lewis R. Gibbes. 
22. Spiraea tomentosa L. Sp. Pl. 489. 1853. 
Spiraea rosea Raf. New Fl. 3: 62. 1838. 
Spiraea ferruginea Raf. New Fl. 3: 63. 1838. 
Spiraea glomerata Raf. New F1. 3: 63.- 1838. 
Spiraea parvifolia Raf. New F1.3: 63. 1838. 
A shrub, 3-12 dm. high; bark of twigs purplish or brown, tomentose; petioles very 
short, 2-3 mm. long; leaf-blades oval, ovate-lanceolate or oblong, usually acute at the 
apex, acute or rounded at the base, coarsely crenate-serrate, dark-green and usually slightly 
puberulent above, densely white- or somewhat rusty-tomentose beneath, 3-6 cm. long, 
1-2.5 cm. wide; inflorescence paniculate, dense and usually narrow, 1-2 dm. long, 3-5 cm. 
wide, its branches tomentose; hypanthium tomentose, hemispheric, less than 1 mm. 
deep; sepals triangular, in fruit reflexed ; petals pink, purplish, or rarely white, orbicular- 
ovate, about 1.5 mm. long; follicles oblong, about 2.5 mm. long, tomentose or arachnoid. 
TYPE LOCALITY: Philadelphia. : 
DISTRIBUTION : In swampy and wet places from Nova Scotia to Georgia, Arkansas, Kansas, 
and Manitoba. 
ILLUSTRATIONS: Raf. Med. Bot. 2: pl. 88; Britt. & Brown, Ill. Fl. f. 1884. 
EXCLUDED SPECIES 
Spiraea hypericifolia L. Sp. Pl. 489. 1853 (S. hypericifolia Plukenetiana Seringe, in 
DC. Prodr. 2: 543. 1825; S. virgata Raf. New. F1.3: 72. 1838; S. Hookeriana Raf. loc. cit. 
73), was based at least in part on Plukenet’s Prunus canadensis. His figure of this plant 
may just as well represent Prunus cunetfolia as the species which has borne the name S. 
hypericifolia l. The latter is not an American plant, although the older botanists repeat- 
edly referred it to this continent. 
Several garden hybrids, especially of S. salicifolia, S. Douglasti, and S. tomentosa, 
have been described. 
3. PETROPHYTUM (Nutt.) Rydb. Mem. N. Y. Bot. Gard. 
1: 206. 1900. 
Spiraea § Petrophytum Nutt.; T. & G. Fl. N. Am. 1: 418. 1840. 
Densely cespitose and depressed undershrubs with prostrate branches, growing on 
rocks. Leaves oblanceolate or spatulate, entire, coriaceous, evergreen, crowded on the 
short branches. Inflorescence racemose, rarely compound. Flowers perfect. Hypan- 
thium hemispheric. Sepals 5, valvate. Petals 5, imbricate, white. Stamens about 
20; filaments filiform, distinct, about twice as long as the sepals. Disk evident, entire- 
margined. Pistils 3-5; ovary and lower part of the style very hairy; style filiform, ter- 
minal; stigma minute, entire; ovules 24, pendulous. Follicles leathery, dehiscent along 
both sutures; seeds linear. 
Type species, Spiraea caespitosa Nutt. 
Leaves 3-ne ved. 
Petals obovate or oval ; leaves sparingly strigose or glabrate. 1. P. Hendersoni. 
Petals spatulate or oblanceolate ; leaves minutely canescent as well as 
strigose. 2. P. cinerascens, 
