1977]1977) ChromosomeChromosome Studies•Studies-KeilKeil 7979
CHROMOSOME STUDIESSTUDIES INI~ NORTHNORTII ANDAND CENTRALCENTRAL AMERICANAMERICAN SPECIESSPECIES OFOF PECTISPEenS L.L (COMPOSITAE:(COMPOSITAE: TAGETEAE)TAGETEAE)
DAVIDDAVID J.J. KEILKEll
Chromosomal modificationmodification isis oftenoflen aa majormajor factorfactor inin thelhl: evoe\'o lutionaryIUlioltllry diversificationdl\'ersiflCalion of aa large,large. rapidlyrapidly evolvinge\ohmg genus.genus. Pectis,PUIU. thethe largestlargesl and most widespread genusgenus inin thelhl: NewNe~ WorldWorld tribetri~ TageteaeTagelC'ae (Compositae),(Composit3e). hashas radiatedradiated intointo a variety\'ariet) ofof habitatshabilats during itsiu evolutionarye\'Olutionarv history.historv. UntilUntil relativelyrclati\'ely recently,recently. how-hollo ever,e\"Cr. littlelillie has beenbeoen knownk~own of the thl: rolerole ofof chromosomal change in thethl: evolutione\olution of the genus. PectisPrctis wasIloas cytologically cy'lologicall) unknownunknown untilunlillhe the studiessludles of RavenRa\"Cn and KyhosK)hOS (1961) andand of Turner,Turner. Elliflli SO'l,son, and King (1961). Subsequently, additional counts haveha\'e beenbttn reported for several taxataxa (Table 1).I), To date, however,ho"e\'er, only a few(~, of thethe species have been studied cytologically, and thesethese only from a few populations.popUlations, Of thelhe fourrour largelargc genera of thelhe Tagcteae,'ageteae, PectisPro;s has been the most poorly representedrepresented inin cytocyto logical studies. This investigation is one of a seriesserics of studies of thethe evolution ~ndand taxonomy of Pectis.Pecfis. The genus reachesreaches itsits greatest diversity mIn the warmer areas of North America,America. and itit isis fromfrom thislhis region that most of thethc collectionscollcctions upon which thisthis study is based were Illade.made. Through an examination ofor the chromosomes of as many species~P«ies as possible,possible. and from numerous populations of wide-"ide ranging ~pccies.species, information regarding thelhe variability\'ariabililY of chromo-chromo SOmessomes inh PectisPur;s can be betterbeller correlated with\loith thelhe: evolutionarye\o]utionary h· historyISlory and syslematlcssystematics of thelhe genus.
MATERIALS\lATEKIA15 "''l:DAND METHODS\IEfHODS Immature capilUbcapitula were killed and fixed in thelhe field in modi-modi· r~led U1moy'sCarnoy's fixalhefixative (4 chloroform:chloroform : 3 elhanolethanol : 1 I glacial acetica~lic aci aetdl.d), and were kept under refrigerationrefrigeralion prior to examinalion.examination. In a modification of lhethe methods of BeeksReeks (1955).(1955), wholeIlohole florclfloret buds --ere^!re slainedGained (usually(usually withoulwithout heal)heat) for 2-48 hourshOUfS in standard Itt0 acClocarmineacet°carmine or iron acelocarmincacetocarmine solution and were\I"Cre squ3!ihcdsquashed ~~OUt[Vltnout Prio~Prior ma~rationmaceration in a drop of Hoyer'sHO)'~r's sol~tlOn.solution. Camera ucidaida draWingsdrawings \\ocrewere prepared from meIoticmeiotic mlcrosporcx)"tesmicrosporocytes to0 documentdocument eacheach reported counl.count. Table I. ~ Table I. Previously'·...iou'l) reportedropor••d chromosomedlOomoo.o.... countsoounh forroo Pectis.1'",... o0 Reported1<,p<>rtN OOunlcount I,,)(n) TaxonTa.Of1 ReferenceRef,rence P. angustifoliadnf:l'tltfolHl Torr.rorr. var.''ilr. dn1:angustifolia....'ijol'" 12 (1"(as P.r .fcf. ,'texana..." .... Co'}lCory) PowellI'o""n &II. TurnerTum•• (1963)(1%3) "12 la.(as P.r. angustifoliaIHlKO'm/oI", Torr.)run-.) PowellF'o".,,11 &II. TurnerTu...... (1963)Il96)) " P. ""1:"-"if''''''angustifolia Torr.Torr.• var.ar. ,~,...II"tenella {DC.)(DC.) KeilI:.il 12 laJ(as P. Im~/'"tenella LX")DC.) Powellpo..,,11 &II. TurnerTum... (1963);(l96ll: StrotherSI,odM" (1972);(1971~ " UrbatchUrhlidl in'10 LoveI ii•• (1974)I 197.) 12 PP..• coulter00"I~n i /faHarv.... &&I GrayGra) Keil(1975B)K,;11I975K) "12 1'.P. ~",n.udepressa IFern. efn. PowellI'o..en &&: TurnerTtl'..... (1963)tl96ll " PP. filipesfibf't'. Ifal'\'Harv. &.t GrayG",) ''iI.var. so