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A Revision of Pectis Section Pectothrix (Compositae: Tageteae)

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A Revision of Pectis Section Pectothrix (Compositae: Tageteae) A REVISIONREVISION OF PECTISPEens SECTIONSECTlO~ PECTOTHRIXPECTOTHRIX (COMPOSITAE.(COMPOSITAE: TAGETEAE)TAGETEAE) DAVIDDA\ID J.J. KEILKEIl PectisP~('lis L.l. sect. PectothrixPUlOlhri.'C A. GrayGray (Compositae:(Compositae: Tageteae)Tageteat) comprises a group of showy,showy. yellow-headedyellow-headed species which.... hich occursoccurs mainlymainl} inin thethe arid and semi-arid portionsportions ofof thethe southwesternsouthwestern UnitedUnIted States .and northernnorthern Mexico.Meltico. AlthoughAllhough severalse\-eral regionalregional floras have includedincluded one or moremore of thethe species inin thisIhis group,group. nono workersworl.:el'$ since Fernald (1897) and RydbergR}dbcrg (1916) have attemptedattempted to10 treatlreal this portion of thethe genus inin itsits entirety.emirely. SinceSince 1916,1916. severalsc\'eral workers have described new taxataxa (Cory, 1937; Johnston,Johnston. 1940;1940: Wiggins,Wiggins. 1951;1951: Keil,Keil. 1974),1974). and manymany new collections haveha\'C beenbttn made. Recent studiessiudies (Keil,(Keil. 1974) haveha\'e suggested thatthat thethe species relationships proposed by earlier workers.... orkers (Fernald,(Fernald, 1897;1897: Gray,Gray. 1884;1884: Rydberg,Rydberg. 1916) should be re-examined.rc-uamined. TAXONOMICTAXO-':O\1IC HISTORYIIISTOR Y The species included in thethe present reportreport belong toto a complexl;omp1ex treatedtrealed in the past as two subgenera, PectidopsisPI'C/i(IQPsis and PectothrixPeclOtllri.r (Fcrnald,(Fernald, 1897). Pectidopsis,Pectitlopsis. originallyoriginall}' described as a mono-mono­ typict}pic genus (DeCandolle.(DeCandolle, 1836),1836). was reduced in rankrank to a section of PectisPI'Ct;s byb}' Gray (1852), and was subsequentlysul>sequenlly mergedmcrged withwilh sect.sec\. £llpt'ClisEupectis by Gray (1884). Fernald (1897) resurrected PectidopsisPu/idopsis as a SUbgenussubgenus and included "'itbinwithin it twelvetwelve species with thethe pappus coromformcoroniform and few-bristledfe .... -bristled or few-awned.few-a'" ned. Pectothrix,putothri:r. dcscnbeddescribed by Gra}Gray (1&49)(1849) as a subgenus of Pectis,PI'C/is, was",,-as reduced to sectional rank three:three years}ears later (Gray.(Gray, 1852).1852), but was""as returned to10 subgcncnesubgeneric 1e\,<:1level in FernakTsFernald's (1897) revision. Throughout its hIstory.history, P~(,'OIh,ixPectothrix has been used for species with""llh a multisetosemulliselOSC pappus. Although RydbergR)"dbcrg (1916).(1916), the last worker to10 revisercvise this part of I'utis,Pectis, did not accept any infragenericIOfragcncric categories, inIn most cases he retained the:the arrangement of sp«iesspecies thatthai FernaldFe:rnald had proposed. RF-F\I\IRE-EVALUATION tAllO' Of-OF 1'\1INFRAGENERIC IlA(,1 '[RtC IlOlBOUNDARIES 'OARIF' Previous imcstigalorsinvestigators have:have e:mphasindemphasized in varying deg~esdegrees thethe' features of thethe pappus as characters for subdividing PeClis,Pectis, firstfirs! J232 1977] Pectis•KeilPectis-Keil 333J into segrcgatesegregate genera (I..es.~ing.(Lessing, 1830, 1831;1831: DeCandolle, 1836), and later into sections or subgem:rasubgenera (Gnly,(Gray, 1849,1849. 1852, 1884:1884; Fernald.Fernald, 1897). Although pappus characters can be used in some cascscases in conjunction with other features in delineating infrageneric categories in PectisPee/is (e.g., .~ect.sect. HeteropectisHe/eropeClis A. Gray), the use of thesethese features alnnc.alone, like any other one-eharaeterone-character taxonomy, isis SUbjectsubject to error. Fernald's a priori reliancerclianee upon pappus char­ acters inin his treatment of subgenera PectidopsisPeClidopsis and PectothrixPeclOfhrix illustrates the problems of such an approach. After field and herbarium studies of a number of the taxa included by Fernald in subg. PeClidop~·i.~Pectidopsis and subg. Pectothrix,PeClofhrix, I began to doubt the naturalness of thesethe.~e subgl'ncra.subgenera. SC\cr.l1Several lines of evidence led me to this viewpoint. First,First. the taxa included in subg.subg. PectidopsisPee/it/opsis sensu Fernald fall into t"Otwo morphologi­ cally dissimilar groups which differ in .severalseveral features (Table 1).I). TablcTable I.1. \lorphologiealMorphological ~rollpsgroups of PectisPeelis subg. PectidopsisJ'ectidopsis sensu Fernald CH>\R>\CTERCHARACTER GROUP I1 GROUP II11 Positionposition of foliar inframarginal or oil glands marginal scatteredscallered apex of immature rounded or narrowly conical, capitUlacapitula truncate acuteacule 'lumbernumber of ray florets 5or85 or 8 ,5 nUmbernumber of disc florets 10-40 5-10 PUbeSCl'nCCPubescence of glandular-glandular­ Corollascorollas puberulcntpuberulent glabrous TheseThes two groups of taxa have different geographical and eco­ceo­ IO~ical•ogical ranges as well, with the taxa of Group I1 occurring in thethe andarid and semi-arid areas of the southwestern United States and nonheron°rthern Mexico.Mexico, and the species of Group II occupying a more SOuthernsouthern distribution, extending well into the tropicstropiOl of Mexico [Vol.[Vol. 7919 34 J4 RhodoraRhodora SUBGENUSSUBGEtWS PECTIDOPSISPECTI OOPS IS SUBGENUS PECTOTHRIXPECTOTHR\X (~: ~;~~.~~.; P. ..ANGUSTíFOLI'A"*" Foi..l,,············· -'. '" _ . ................. ~ P,P. FILIPES FILl PES .•.... P.P. PALMERIPAUtERI : P. PRINGLEIPRINGLEl GROUP I P,P PAPPOSA PAPPOS~ : P.p, ROSEI ROSEl • P, STENOPHYLLA STEtIOPHYL.1.A .: : P. RUSSYI P. P. RUSBYI ............,.... :.. P. TENELLA TEKELLA •.•.•.•••••.••.•••.•.•••••••• ", . " " . ..-...­ .... ~ p,P. BERLANDIERÎ" BERLANDIEiii··· .. •••·••••· .••••••••••.•• ........... ~ P. CAPILLARISCAPILLARIS P ..•.•.•• P,• DIFFUSADIFFUSA : P,P. DICHOTOMAOJ CHDTOM GROUP II P P.• ELONGATAEL011GATA : P. FASCICULIFLORAFASCICULlFLORA •••...••••. - . ........... .... \ p,P. UNIARI~~~~~UNIARISTATA .............•. ······· .......... ..... P. FASCICULAT" FASCICULATA P.p, CANESCENS P. HAENKEANAHAElIKEA.NA P. LIEBMANNLlEBKANNII I I P. LONGIPES P.P, AQUATICAAQUATIC" fiFigure....e I.1. Rflall"Relationships....bJpo llmOllIamong ~species includedindudcd by FernaldHfn:llid in PectisP,'WJ sub-lUb­ amel1lgenera ~'idopJ"Pectidopsis and hnOl_i-<Pectothrix. andand CentralCentral Amc:rica.America. Second.Second, ifif J-ernald'sFernald's taxonomyluonomy is followed,foUo\Ooeil. each of these groups of species has a counterpancounterpart in his subg. PI'('IO/h"x.Pectothrix. Thus somesome species of subg. PI'('lidoP5isPectidopsis appear to10 be more c10stlyclosely related to some species of subg. PectothrixPUIOIh,/x than they dodo toto other speciesspecies of theirtheir o\Oo'nown subgenus (Figure 1).I). 1917)1977] PeclisPectis•Keil Keil 35J5 The morphological similarity between taxa of different sub-sub­ genera reflects lhcthe biological proximity of these species. Among lhethe species of Group I (Figure 1),I), several cases of interspecific hybridi7l11ionhybridization involving taxa from bothbOlh subgenera havehaw been ob­olr served (e.g(e.g.,.. PectisPeni.'! f'Uf'f'O$Opapposa X P. ol/gwr!(olilJ.angustifolia. P. papposaPUI'flWIJ X P.p, filifWS).filipes). The hybrids are generally r:llherrather vigorous and fertileferlile and evidenC1:evidence of backerossingbackcrossing to thelhe parentparei'll species has been found.found. This hybridi7alionhybridization is an indicationindicalion of the close relation­rclalion­ ship of the parent taxa. In one case,ea~e. taxa of Fernald's different subgenera have even proved to beIloe conspecific (P. palmeripurJl/ai of subg. 1'eflol/tr;.'(;Pectothrix is the same as P.I'. rusbyirushri of subg. Pectidopsis).Pef/idvpl;S). A final line of ev"idencrevidence is the variability"'ariability of the pappus itself.ilself. In Somesome species (e.g(e.g.,.• PectisPeCl;S IlI/KIISr!ro!ia.angustifolia, P. papposa,PllppOSU. P.1'. rusbyi),rusbp1. the pappus is sometimes so variable at the population level that the reliability of even infraspecific classifications,classifications. which relyrely on pappus structure.structure, are doubtfuLdoubtful. Based upon this evidence.evidence, I have redrawn thelhe infrageneric boundaries to reflect more aet;uratel)accurately thelhe species relationships.relationships, [I have chosen to designate the newly defined infragcnericinfrageneric taxon for which the species of Group I (Fi,2ure(Figure 1)/) form a nucleus, as a ~ctionsection rather lhanthan as a subgenus. In rejectingreJccting the subgenus inin favor of the ~ction.section, I am following the lead of Gray (1884) who.... ho wrOlewrote concerning Pectis:Pet:I;S: 'The"The genus is very natural; and, althoughallhough two or lhrrethree genera have been made from it,il. itit seems incapableincapable of°f division even into well-marked subgenera."subgenera.~ In my opinion, the degree of differentialiondifferentiation among the species of PectisPet:lis isis notnOI sufficientsufficient to justify lhethe recognition of subgenera. The name.name, Pct:lidopsis,Pectidopsis, cannOIcannot be used for the newly defined section, because the provisions of Article 21 of thelhe InternationalImernOlional Code of Botanical NomenclatureNomendOlUre (Slafleu.(Stafleu, 1972) prohibitprohibil itsits use alat eilhereither the sectional or subgeneric level within Pectis.P('("/is. However,Howewr, oneone of the twolwo original species of sect. PectothrixPet:lolhr;x (for which no ~ypetype species was ever designated).designated), P. papposa,papposo. is now included Inm lhethe section as I have defined it. I have designated P. papposaPOppOSIl as the lectotype species of sect.~ct. Pectothrix,Pectothr;x, which is thus adopted as thethe
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