462 COMPOSITE, (composite family.) 



72. CENTAUHEA, L. Star Thistle. Centaurea. ShauTc-ed- 



Darddr. 



Heads heterogamous, the marginal flowerets sterile, rarely homo- 

 gamous. Involucre imbricated, scales in several rows, leathery or 

 membranous, spiny or unarmed, entire, ragged, or fringed. Receptacle 

 bristly. Anthers caudate at base ; filaments papillose. Akenes general- 

 ly smooth ; hilum lateral ; pappus persistent (rarely 0), of two forms, 

 the outer consisting of several row^s of bristles or pales, the inner of 

 one row of connivent pales — Perennial, biennial, or annual herbs. 



I. Scales of involucre obtuse, or ending in a tender cicsp, with a trans- 

 lucent, eroded or fringed, hut not ciliate margin. Flowerets rayed. Peren- 

 nials. 



1 C. pergamacea. 



II. Scales of involucre ending in a pectinate-ciliate, mucronate appen- 

 dage which is not decurrent. Flowers 'not radiate. Perennials. 



3 C. Cassia. 



III. Scales of involucre with a scarious, 2^^ctinate fringed, decurrent 

 margin. Flowers blue or violet, .02 to .035 troad. 



'^ Annuals. Akenes bald or pappose. 



3 C. Cyanus, 4 depressa, 5 cyanoides. 



* "^Perennials. Akenes pappose. 



6 C. axillaris. 



IV. Scales of involucre white-ciliate, ending in a weak prickle. Heads 

 oblong, less than .(il long. Annuals. 



7 C. Ammocyanus, 8 laxa. 



V. Stems and branches rigid. Heads oblong-cylindrical, .008 to .015 

 long, .002 to .005 broad ; scales of involucre with a narrow, membranous, 

 pectinate-fringed, margin, more or less decurrent, and ending in a point or 

 short prickle, shorter or somewhat stronger and longer than the- lateral 

 fringes. Biennials or perennials. 



9 C. virgata, 10 leptocephala, 11 aggregata, 12 dumulosa 

 13 Damascena. 



VI. Heads from .015 to .05 in diameter. Scales of involucre scarious 

 or leathery indurated, fringed above, rarely entire, usually ending in a 

 long, stout, prickly sp>ine. Perennials. 



* Plants with stems, usually tall. Leaves not decurrent. 



14 C. Antiochia, 15 speciosa, 16 eryngioides, 17 carduiformis, 

 18 thrincisefolia, 19 Urvillei. 



* * Plants with tall stems. Stem-leaves more or less decurrent. 



t Flowerets purple. 

 20 C. arifolia, 21 Cataonica, 22 spicata, 23 Haussknechtii, 

 24 Doddsii, 25 foliosa. 



1 1 Flowerets yellow. 

 26 C. onopordifolia. 



