PNW432 IDENTIFICATIONIDENTIFICATIONIDENTIFICATIONIDENTIFICATION ofofof KnapweedsKnapweedsKnapweeds andandand StarthistlesStarthistlesStarthistles ininin thethethe PacificPacificPacific NorthwestNorthwestNorthwest A Pacific Northwest Extension Publication Washington • Oregon • Idaho ByCindyTalbottRoché,M.S.,formerWashingtonStateUniversity CooperativeExtensioncoordinator,andBenF.Roché,Jr.,Ph.D.,WSU CooperativeExtensionrangemanagementspecialist,deceased. IllustratedbyCindyRoché. PNWbulletinsareavailablefromcooperativeextensionofficesincounty seatsandfromthepublicationofficesattheland-grantuniversitiesin Idaho,Oregon,andWashington.Otherbulletinsareavailablefromthe publishingstate. Washington BulletinOffice CooperativeExtension WashingtonStateUniversity P.O.Box645912 Pullman,WA99164-5912 509-335-2857or1-800-723-1763FAX509-335-3006 email:[email protected] web:http://pubs.wsu.edu Idaho AgriculturalPublications UniversityofIdaho P.O.Box442240 Moscow,Idaho83844-2240 208-885-7982FAX208-885-4648 Oregon ExtensionandStationCommunications OregonStateUniversity 422KerrAdministration Corvallis,Oregon97331-2119 541-737-2513FAX541-737-0817 email:[email protected] web:http://eesc.orst.edu Montana ExtensionPublications MontanaStateUniversity Bozeman,MT59717 406-994-3273 Usepesticideswithcare.Applythemonlytoplants,animals,orsiteslisted onthelabel.Whenmixingandapplyingpesticides,followalllabelprecau- tionstoprotectyourselfandothersaroundyou.Itisaviolationofthelaw todisregardlabeldirections.Ifpesticidesarespilledonskinorclothing, removeclothingandwashskinthoroughly.Storepesticidesintheiroriginal containersandkeepthemoutofthereachofchildren,pets,andlivestock. CONTENTS Introduction ...................................................................................................... 1 Keytotheknapweedandstarthistlespecies ............................................... 2 Descriptionofthespecies Yellowstarthistle(Centaureasolstitialis) ........................................................ 5 Maltastarthistle(C.melitensis) ....................................................................... 6 Sicilianstarthistle(C.sulphurea)..................................................................... 7 Purplestarthistle(C.calcitrapa) ...................................................................... 8 Iberianstarthistle(C.iberica) .......................................................................... 9 Squarroseknapweed(C.virgatassp.squarrosa) ......................................... 10 Diffuseknapweed(C.diffusa) ...................................................................... 11 Cornflower(C.cyanus) .................................................................................. 12 Mountainbluet(C.montana) ........................................................................ 13 Featherheadknapweed(C.trichocephala) ................................................... 14 Spottedknapweed(C.maculosa) .................................................................. 15 Short-fringedknapweed(C.nigrescens)...................................................... 16 Bigheadknapweed(C.macrocephala) .......................................................... 17 Blackknapweed(C.nigra) ............................................................................ 18 Meadowknapweed(C.nigraXC.jacea) ..................................................... 19 Brownknapweed(C.jacea)........................................................................... 20 Russianknapweed(Acroptilonrepens) ........................................................ 21 Additionalreading ........................................................................................ 22 ffff INTRODUCTION Identification of Knapweeds and Starthistles Knapweedandstarthistleidentificationcanbeadauntingtaskto individualsnotfamiliarwiththisgroupofinvadersfromtheOld World.ExceptforRussianknapweed,alloftheknapweedsand starthistlesinthisbulletinbearthegenusnameCentaurea.Centaureaisa large,complexgenus,whichhasabout1,350speciesnamesvalidly publishedinthebotanicalliterature.Toaddtotheconfusion,some specieshybridize:232hybridsarerecognizedwithapublishedname. Sofar,fewerthan20specieshavenaturalizedinwesternNorth America.Thisnumberincludesseveralofthe25orsospeciesofCentaurea incultivationasornamentalflowers.Oneself-perpetuatinghybrid, meadowknapweed,iswellestablishedinthePacificNorthwest. ThesinglemostimportantcharacteristicinidentifyingCentaurea speciesistheappearanceofthebractsthatsurroundtheheadofflow- ers.Bractsarecomposedoftwoparts,acenterpartandanappendage. Appendagescomeinvariousshapesandmayappearfringed,paperyor translucent,raggedlytorn,andspiny. Youshouldalsonotecharacteristicsofseeds,leaves,roots,and branchinghabittodifferentiatespecies.Flowercolorisnormallyimpor- tantonlyinseparatingtheyellow-floweredgroupfromthegroupwith whiteandrosetopurpleflowers.Mostspecieswithpinktopurpleflow- ersmayhavewhiteflowers.Amongourspecies,onlythecultivated sweetsultan(Amberboamoschata,formerlyCentaureamoschata)hasaswide acolorrangeascornflower(Centaureacyanus).Sweetsultanflowersmay beyellow,white,pink,rose,orpurple.Cornflowerflowersmaybeblue, white,pink,rose,lavender,orpurple.Allflowersaretubulardiskflow- ers,althoughinsomespeciestheouterringflowersineachheadare enlarged,orradiate.Theseradiateflowersareoftensterile. Thefollowingkeyassumesthatyouaretryingtoidentifyaflowering plant.Vegetativespecimenscanbeextremelydifficulttoidentify.Ifflowers arenotavailable,lookforthedistinctivebractsonbudsandespeciallyon theweatheredseedheadsfromthepreviousyear’sflowers.Donotassume thatthenameyouarriveatinthekeyiscorrect.Checkyourspecimen againsttheillustrateddescriptionsfollowingthekey.Forinformationon biology,habitatandmanagementalternatives,refertotheextension bulletinsreferencedforeachspecies.Forchemicalcontrolrecommenda- tionsandalistofavailablebiologicalcontrolinsects,refertothePacific NorthwestWeedControlHandbook.Sourcesforbulletinsappearonthe insidefrontcover. 1 KeytotheKnapweedandStarthistleSpecies(naturalizedinthewesternUnitedStates) Descriptionsandmeasurementsofbractsrefertothemiddlerowsonthehead. 1a. Bractsthatsurroundtheflowerheadarespine tipped __________________________________________ 2 2a. Stemleavesformwingsdownstems,flowersyellow, plantsannual _____________________________________3 3a. Spineattipofbractroundincrosssection;yellowor straw-colored,withtwopairoflateralspinulesat 3a baseofterminalspine;annual yellowstarthistle(C.solstitialis) 3b. Spineflattenedorgroovedontop,brownorpurple tinged,especiallynearthebase_______________4 4a. Spine1/4to3/8inchlong,withlateralspinesnear thetopandthebase;headsupto1/2inchin diameter Maltastarthistle(C.melitensis) 4a 4b. Spine1/2to3/4inchlong,darkpurple,with 3to4slenderlateralspinesoneachsideofthe baseofthemainspine;headslarger,1inchin height;seedsshinydarkbrownwithbristly blackpappus;plantannual 4b Sicilianstarthistle(C.sulphurea) 2b. Stemsnotwinged,flowersvariouslycoloredbutnot yellow;lifespanvariable _______________________5 5a. Spineattipofbract3/8to1inchlong,oftenbrown orpurpletingednearbase,obviouslygroovedontop; flowerspurpleannualorbiennial ______________ 6 6a 6a. Seedwithpappus Iberianstarthistle(C.iberica) 6b. Seedwithoutpappus 6b purplestarthistle(C.calcitrapa) 5b. Spineattipofbractabout1/8inchlong,spreading orcurvedbackward,longerthanspinesonsides ofbract ___________________________________7 7a 7a. Spineattipofbractstronglycurvedbackwards; flowersrose-purple;entireheadfallsoffat maturity;planttaprootedperennialwithmany persistentflowerstalks squarroseknapweed(C.virgatassp.squarrosa) 2 7b. Spineattipofbractspreading;flowerswhite, cream,palelavender,orpurple;plantnormally biennial(sometimesannualorperennial), taprooted;bushystalksbreakoffatbaseto tumblewithseedheadsintact diffuseknapweed(C.diffusa) 7b 1b. Bractsnotspinetipped ____________________________ 8 8a. Bractappendageisacomblikefringeorraggedly torn,butwithoutawidepaperytranslucent margin _______________________________________ 9 9a. Appendagesofadjacentbractsdonotoverlap obviously ________________________________ 10 10a. Edgesofbractsawl-shapedorappear raggedlytorn,notdrawnoutandneedlelike; centerpartofbracthasverticalveins, marginsoftenbrown __________________ 11 11a 11a. Leafbasesnotwinged,leavesmostly entireorloweroneslobed;flowersblue, purple,white,orrose;uprightannual cornflower(C.cyanus) 11b 11b. Leafbasewinged,leavesentireor toothed;flowerheadshaveoutsidering blueandinnerflowersviolet;perennial, hascreepingrootstalks mountainbluet(C.montana) 10b. Bractappendagehasneedlelikeorcomblike fringe _______________________________12 12a. Comblikeappendagesonbractsequally 12a spacedoneachside,tipofbract recurvedbackoverthebase;flowers pinkorpurple;perennial featherheadknapweed(C.trichocephala) 12b. Bractswithbrowntriangulartip ___13 13a. Leaves,exceptthoseontheupper- 13a moststem,dividedintonarrow segments,lowerleavesstalked; seedsnormallyplumed;perennial spottedknapweed(C.maculosa) 13b. Leavesentireorlobedonmargins butnotnarrowlydivided,stalkless; 13b seedplumeless;perennial short-fringedknapweed(C.nigrescens) 3 9b. Fringesofbractsoverlapthoseofadjacent bracts ____________________________________ 14 14a. Stemswollenbeneathheadofyellow flowers;head1to3inchesindiameter; 14a bractshavethinandsomewhattranslucent fringedmargin;lowerbractshaveaweak centralspine;perennial bigheadknapweed(C.macrocephala) 14b. Flowersrose-purpletowhite,stemsnot obviouslyswollenbeneathflowerheads, headsmultiple,lessthan1inchin diameter_____________________________ 15 15a. Fringeofbractblack,twoormoretimes aslongasthewidthofthecenterofthe