Home Flora of Missouri
Home
Name Search
Families
Volumes
!Centaurea diffusa Lam. Search in The Plant ListSearch in IPNISearch in Australian Plant Name IndexSearch in NYBG Virtual HerbariumSearch in Muséum national d'Histoire naturelleSearch in Type Specimen Register of the U.S. National HerbariumSearch in Virtual Herbaria AustriaSearch in JSTOR Plant ScienceSearch in SEINetSearch in African Plants Database at Geneva Botanical GardenAfrican Plants, Senckenberg Photo GallerySearch in Flora do Brasil 2020Search in Reflora - Virtual HerbariumSearch in Living Collections Decrease font Increase font Restore font
 

Published In: Encyclopédie Méthodique, Botanique 1(2): 675–676. 1785. (Encycl.) Name publication detailView in BotanicusView in Biodiversity Heritage Library
 

Project Name Data (Last Modified On 8/11/2017)
Acceptance : Accepted
Project Data     (Last Modified On 7/9/2009)
Status: Introduced

 

Export To PDF Export To Word

3. Centaurea diffusa Lam. (diffuse knapweed, tumble knapweed)

Pl. 251 g; Map 1042

Plants annual or less commonly perennial, usually with a taproot, pubescent with cobwebby hairs when young, not appearing pale or whitened, sometimes nearly glabrous at maturity. Stems 20–90 cm long, erect or ascending with loosely ascending or spreading branches at or above the midpoint, somewhat angled but not winged. Leaves 2–20 cm long, often dotted with minute, yellow to brown resin glands; basal and lower stem leaves with the blades mostly 12–80 mm wide, oblanceolate to obovate, rounded or angled to a bluntly pointed tip, tapered gradually to a sessile or short-petiolate, usually somewhat expanded base, 2 times pinnately lobed, the margins otherwise entire or finely toothed; median and upper stem leaves gradually reduced, mostly sessile, the base sometimes slightly clasping the stem, not or only slightly decurrent, the blades linear to oblong-oblanceolate, entire or rarely toothed or lobed, occasionally 2 times pinnately lobed. Heads solitary at the branch tips. Involucre 10–13 mm long, longer than wide, narrowly ovoid to narrowly ovoid-cylindrical. Lower and median involucral bracts with the body ovate to narrowly ovate, the margins fringed with small, slender, straw-colored spines, the outer surface glabrous or slightly cobwebby-hairy, not concealed by the appendages; the apical appendage well differentiated, ascending, narrower than the main body, not or only slightly overlapping, straw-colored or pale greenish-tinged, the involucre often entirely straw-colored, the margins with a fringe of slender, spreading teeth and a short central spine, this 1–3 mm long. Upper involucral bracts lanceolate, the appendages not well differentiated from the relatively broad (at least toward the tip), thin, white, papery margins, the tips usually sharply pointed, irregularly toothed or narrowly lobed. Florets all discoid, the marginal florets appearing discoid but functionally sterile. Pappus absent or of minute, bristly scales, these 0.1–0.5 mm long, white, usually persistent at fruiting. Corollas 9–13 mm long, cream-colored to nearly white, rarely pinkish- or purplish-tinged. Fruits 2.5–3.5 mm long, somewhat flattened, the attachment scar appearing lateral, the surface usually dark brown, usually glabrous and somewhat shiny. 2n=18. June–September.

Introduced, known thus far only from the city of St. Louis (native of Europe; introduced widely in the western and midwestern U.S. and adjacent Canada, also sporadically in the northeastern U.S.). Railroads.

Steyermark (1963) reported this species based on collections made by Viktor Mühlenbach in the St. Louis railyards. However, some of Mühlenbach’s collections and also a later one from Howard County are actually the fertile hybrid between C. diffusa and C. stoebe, which has been called C. Hpsammogena Gáyer. This hybrid is variable, but generally differs from C. diffusa in its less divided leaves with narrower lobes (more like those of C. stoebe), slightly broader heads with well-developed marginal raylike florets, and involucral bracts with a shorter central spine at the tip (Ochsmann, 1997, 2001b). True C. diffusa is represented by only two of Mühlenbach’s several voucher specimens. The species is a widespread weed in the northern and western United States and Canada that may have been spread into Missouri by the transport of hay or livestock.

 
 


 

 
 
© 2024 Missouri Botanical Garden - 4344 Shaw Boulevard - Saint Louis, Missouri 63110