1700 



SPIRAEA 



KEY TO THE SECTIONS. 



A. Lvs. always entire: fls. in simple or panicle d 

 racemes: follicles usually 2-seeded. (Bo- 

 tryospira, Zabel.) 

 B. Plants tufted, suffruticose: fls. perfect, in 



usually simple racemes 



SECTION 1 . PETROPHYTUM ( Species not in cult. ) 

 BB. Plant an upright shrub with stout branches: 



fls. polygamous in panicled racemes 



SECTION 2. SIBIR^EA (Species No. 1) 

 IA. Lvs. usually serrate, rarely entire: fls. in 

 umbel-like racemes, corymbs or panicles: 

 seeds several. 

 B. Inflorescence a simple umbel-like raceme: 



fls. white 



SECTION 3. CHAM^EDRYON (Species Nos. 2-20) 

 BB. Inflorescence compound: fls white or pink. 



0. Fls. in corymbs 



SECTION 4. CALOSPIRA (Species Nos. 21-36) 



CO. Fls. in panicles 



SECTION 5. SPIRARIA (Species Nos. 37-49) 



SECTION!. PETROPHYTUM (Species not in cult. ). 



This section contains a few rather rare American spe- 

 cies of which none is in cultivation. The best known 

 is S. caespitosa, Nutt. (Petrophytum ccespitdsum, 

 Rydb. ) , a dwarf cespitose subshrub, only a few inches 

 high, with crowded, small, entire Ivs. and small, whitish 

 fls. in dense, usually simple racemes on slender stalks 

 arising from the tufts of the grayish green foliage. It 

 is very unlike any other Spirea and more resembles in 

 habit a Saxifraga. It is perhaps better regarded as a 

 distinct genus like the allied Kelseya unifldra, Rydb. 

 (Kriogynia unifldra, Wats.), and Uriogynia pectinata, 

 Hook. 



SECTION 2. SIBIR^EA (Species No. 1). 

 1. laevigata, Linn. (S. Altaica, Pall. Sibircea Icevi- 

 gata, Maxim.). Shrub, 5 ft. high, with stout upright 

 branches : Ivs. cuneate-oblong, bluish green, glabrous, 

 l%-3% in. long: fls. polygamous, greenish white in 

 terminal panicles, 3-5 in. long, those of the staminate 

 plant somewhat showier. May. Siberia. Hardy. 



SPIREA 



SECTION 3. CHAM^EDRYON (Species Nos. 2-20). 



A. Fls. in sessile umbels, with none 

 or very small Ivs. at the base or 

 only the lower umbels on leafy 

 stalks. 



B. Foliage entire orcrenately den- 

 tate only near the apex, often 



3-nerved, grayish green 2. hypericifolia 



BB. Foliage dentate or set-rate, usu- 

 ally penninerved, bright 

 green. 



C. Shape of Ivs. linear-lanceo- 

 late: glabrous 3. Thunbergi 



CC. Shape of Ivs. ovate to oblong- 

 lanceolate : finely pubes- 

 cent when young. 

 D. Umbels on the lower part 

 of the branches stalked. 



E. Lvs. oblong 4. arguta 



BE. Lvs. obovate 5. multiflora 



DD. Umbels all sessile, 3-6-fhl. 0. prunifolia 

 AA. Fls. in um,bel-like racemes on 



leafy stalks. 



B. Margin of Ivs. entire or crenate 

 or dentate only toward the 

 apex. 

 C. Foliage grayish pubescent 



on both sides 7. cana 



CC. Foliage almost glabrous. 

 D. Shape of Ivs. elliptic to 



oblong-lanceolate. 

 E. Lvs. penninerved: 



shoots angular 8. alpina 



EE. Lvs. all or partly 



3-nerred. 

 F. Shoots striped: Ivs. 



all 3-nerved 9. crenata 



FP. Shoots terete: Ivs. 

 partly penninerved, 



partly 3-nerved 10. Pikowiensis 



DD. Shape of Ivs. almost or- 

 bicular, %-l in. broad. .11. bracteata 

 BB. Margin of Ivs. incisely serrate 

 and often slightly lobed (only 

 in No. 19 sometimes entire). 

 0. Stamens shorter than or as 

 long as petals: sepals 

 erect or spreading in ' 

 D. Foliage glabrous. 



E. Form of Ivs. orbicular 



to ovate. 



F. Apex of Ivs. obtuse. 

 G. Lv s. penninerved, 



ovate 12. Blumei 



GO. Lvs. palmate ly 3-5- 



nerved, orbicular. 13. trilobata 

 FF. Apex of Ivs. acute... 14. Van Houttei 

 EE. Form of Ivs. rhombic- 

 lanceolate 15. Cantoniensis 



DD. Foliage pubescent, at least 



beneath. 



E. Umbels and follicles 

 pubescent. 



F. Tomentum grayish. .1(5. blanda 

 FF. Tomentum yellowish. 17. Chineusis 

 EE. Umbels and follicles 



glabrous 18. pubescens 



CC. Stamens longer than petals: 



sepals re flexed. 

 D. Shoots terete, often pubes- 

 cent in fruit 19. media 



DD. Shoots angular, glabrous. 20. chamaedry folia 



2. hypericifdlia, Linn. Vigorous shrub, 5 ft. high, 

 with slender arching or upright branches: Ivs. almost 

 sessile, cuneate-obovate to obovate-lanceolate, 3-nerved 

 or with few lateral veins, almost glabrous, %-!% in. 

 long: fls. small, white, in sessile umbels; pedicels usu- 

 ally pubescent; petals almost orbicular, usually longer 

 than stamens. April, May. S. E. Eu. to Siberia. Va- 

 riable species. Var. acutifdlia, Wenzig (S. acutifolia, 

 Willd. S. hypericifolia, var. acuta, Ser. ). Lvs. nar- 



