A NATURAL INTERGENERIC HYBRID IN THE x = 6 GROUP OF THE ASTEREAE (ASTERACEAE)

9 Pages·1991·3.5 MB·English

by  Ronald L Hartman

A NATURAL INTERGENERIC HYBRID
IN THE X = 6 GROUP OF THE
ASTEREAE (ASTERACEAE)
RONALD HARTMAN
L.
RockyMLoaurnamtiaei,nWHeYrba8r2i0u7m,1-U3n1iv6e3rsitUy.So.fAW.yoming
,
and
MEREDITH A. LANE
R. L. AlcGregorHerbarium, UniversityofKansas
2043 ConstantAve., Laurence, KS66047-3279, U.S.A.
ABSTRACT
A single plant found westofZacatepec, Puebla, Mexico, is recognizedasa hybrid
betweenmembersoftwox~ 6generaofAsrercaebasedonintermcdiacyofcharactersand
reducedfertility.TheplantisregardedasXanfhocephaiumhum/Ie{Kunth)Benth. X Isocoma
(liap/opapp//s)veneta(Kunth)E.Greene.Theexistenceofthisandtwoothernaturalhybrids
ofsimilaroriginsupportsthehypothesisthatthegeneraofAstereaehavingx=6aremore
closelyrelatedtooneanotherthananyistogenerahavingotherbasechromosomenumbers,
butshouldnotbeinterpretedasevidenceforunitingthegenera.
KEY WORDS: Asteraceae, Astereae, Haplopappus, Isocoma, Xanthocepha/»m, hybrid,
Mexico.
RESIJMEN
UnaplantaencontradaaloestedeZacatepec,Puebla,Mexicohasiclorcconocidacomo
unhibridoentredosx = 6generosdeAstereaebasadoenfertilidadreducidaycaracteres
intermedios. LaplantaesconsideradaXanthocephalumhumile(Kunth)Benth. X Isocoma
(Haplopappus)I'ene/a(Kunth)E.Greene.Laexistenciadeestcyotrosdoshibridosdeorigen
naturalsostienelahipotesisdequelosgenerosdeAstereaequetienenx ~ 6estanmas
cercanamenterelacionadosunosaotrosquecualquieradeestosconotrosgeneroscondif-
crenres numeros cromosomicos base, no obstante esto no debe set interpretado como
cvidenciaparaunitlosgeneros.
FoundwestofZacatepec,Puebla,Mexicowasasingleplant,Hartman&
Funk 4/27, 19 Aug 1976 (RM and TEX), which has the following
combination offeatures unlike that ofany plant previously known to
science:
Sprawling perennial herb, stems longitudinally ridged, 1")—25 cm long, reddish-
browntopurple,denselyvillous,lesssowithage,theintcrnodes2—12mmlong.Leaves
alternate,oftenwithfasciclesofsecondaryleavesinaxils,lanceolatetolinear-lanceolateor
occasionallylinear,15—M)mmlong, I—5mmwide,theapexmucronare,thebasegradu-
SioA 14(3):-^21-.329. 1991.
322
allyt.ipcrc'd,rhcmartiniswith1—3(-4)s.ilicnt,mucronaterecthpcrsiilc,i)ftcnnorpaired,
theatlaxialSLirfaeesparselytomoderatelyvillous,pittedondrying,',theveinsobscure,less
soontheslightlypalerabaxialsurface,(^apitulescenceaterminal,corymboseclusterof
4—8heads;petluncles')-3()mmlong,bracteate,thebractslineartoscale-like,densely
vhHiiolgwlheo,ru,s,7—7s9—pa-r95s.e5lmymmsmowiwhdiietg,hhtahgieen.pthrHyulietlaadr(ipscrsetsaisdneida^tem—,at4e7r(i~-a5Sl));.mseirminevso,hliuigcmhrbersiacnahdteem,i1siop—bhleo1r<niScgm,tmo")n—wari6rdoemwlmiyn
oubpl|axi-irce1o/l2at—e,l/ai|ihpreersbsaetcie,ousI,—3themampexlomnugc,rotnhaetel;owreerceppotratclieosnHtahtictkoesnleidg,htlsytrcaomnivneexo,usa,lvteho-e
late,ihealveolaerimmedbyscales0.2-O.')mmlong.RayHoretshermaphroditic(Fig.
lA), 12—I');corollayellow,thetube 1.^-2mmlong,0.3-0.4mmindiameter,mod-
se3lrroaintgge,mIla,yt1ni.toct8>tt—dwheer2nl.osl2uegldmhyeovmuveitllowloiporteuldswe;,i(tsFwhtiiygdtl.eheltbl1arAt)ane,neracvhptehepsese,nld1taa.hmge-iie-nlsoa;b1e.abs5crhoimearndrmeelgyuollbooalnrbo,gl,no0gn.egit1toh—toeo0br,oelvl5iloinipemdtai,rmc,a1ln.5od9n-ga6;p.1pa5enz7atrhmmienrmmgs
long,tan,antrorsely|-iubescent;pappusbristlessomewhatunetjual, 1.5—2.5mmlong,
tan. Disc Horets hetmaphroditic, 32-10; corolla yellow, goblet-shaped, the tube
2lo.n5g—,20..78—mm0.9lomngm,0i.nid—i0am.e4temr,mglianbrdoiuasm,etetrh,eslpoabresselnyarvrilolwoluys,trtihaengtuhlraora,t01..25--0.1.75mmmm
long,glabrous;anthers5,functional;stylebranches1-1.2mmlongwithdeltateappend-
eagqeusa;l,a2ch-ene[mombovlooindg,,t2a.n.8-Me3ximcom:Pluoenbgl,a:tasna,ltafnltatro(resleevl.ycpa.ub2e3sc0e0ntm;),pcaap,p4u.s8bkrimstlWesNuWn-
ofZacatepecon hwy \^('>. WithXiiiitht>iej)hi/hanhitmile, scattered individualso'iIioconid
iviu'lii,andspeciesotlirii^^eriDi.SiiiiaLi.Atriplcx.bmitdoua,andDistnhlisintheimmediate
vicinity.
Therearetwopossibleexplanationsforthechfferencesbetweenthisplant
anc] known species: either it is a new species, or it is a hybrid between
related butdistinct taxa. Based on thedatagiven below, we believe the
latterto bethe case.
The plant was found with Xauthoaphalumhuniile(Kunth) Benth. and
Isoamia veneta (Kunth) E. Greene {= Haplopapptn vemtns (Kunth) S. V.
Blake],twospeciesotagroupofgeneraoftheAstereaethatseveralauthors
haveconsideredtoberelated.Thebasesforthisassessmentarethecommon
basechromosome numberofx = 6andshared morphologicalcharacters
including goblet-shaped disk corollas (first noted by Jackson 1966),
deltate style-branch appendages on the disk florets, and rectangular
epidermalcellsontheadaxialsurfaceoftheraycorolla,asshowninFigure
IC(Hartman 1990;Hartmanctal. 1987;Lane 1980, 1982;Lane&Hart-
man 1984, 1985;Laneetal. 1987)amongotherfeatures(DeJong&Bea-
man 1963;Keil&Stuessy 1977).Inaddition,manymembersofthegroup
grow in saline or alkaline habitats (Robinson 1893; Steyermark 1937;
Turner 1972; Mayes 1976; Watson 1977; Lane 1983). Further,Jackson
(1966),Jackson& Dimas(1981), andVenugopalan(1966)havereported
experimentalhybridsbetweensomeofthespeciesbelongingtothisgroup
323
m).riACi..'l1u.bSecaanntniinlogwcelrctptorrorniomnicofrolgarmaipnhasooffararyayfifolroertest(fsrcaolmeIfohrirAlm=an&1mVmii,nkst4a1l2e7fo(rRBMa)nsdhCowi=ng50th(eX
poorlyticvelopedanthers(lightcolored)inproximitytotworudimentaryadaxiallobes(darkcolored)
andthevillosetube.U. AdaxialepidermisofthelaminaofaHorecshowninFig. lA.C.Adaxial
epaptitdeerrnmitsyopifctahlelofa^mailnlamole'mabreayrst\orio:fr:otfheXt.ivnl=/me6phgaehn/emrlai//omf/h{ALsctie/rue'a2e_.V)5Sp,eTFc.iXm)e,nsshwoewriengparnepeapriedderamnald
photographedasdescribedbyLane(1982).
all)F.lCAl..2X.unStcbaonLntipnhgaleulmecthrioinmimkiciLraoigiera2pVh>s^o,fTadIaJxXi)a.lBsu.rfHaicteisinoufiluob&esFoufndkis4k1c2o7rol(lRaMs)(.scaCl.eI=soc"o3m0.j|ximvnefloar
e(HpaiydlenritmDail^pHa]t()t,erTnEsXh)o.wnSpeiscitmypeincsalweorfealplrempeamrbeedrasndofphthoeto/g/r=aph6edgeansedreascofribAsetderbeyaeL.ane(1982).The
.
324
()i\^cncra; Lane(1980, 1983) found rwo natural interspecific hybrids in
Xanthocephcil//iii
HartnuDi & Viink 4127 shares a number offeatures with both ofthe
parentalspeciesproposedhere.Theepidermalcellsoftheadaxialsurfaceof
thediskcorollalobesareidenticaltothoseofbothX. hmmleand/. veneta
(Fi^s. 2A-C), the disk corollas are goblet-shaped, the disk style-branch
appendagesaredeltate,andtheplantwasfoundinasalinehabitat. How-
ever,whilethepollenstamabilityofbothspeciesis98%orgreater(Jackson
&Dim-ds 1981;Lane 1980;seeTable 1),thatoftheputativehybridisonly
51.4% (205 of399 observed grains were stained in lactophenol cotton-
blue). Further, only 11 of 19 (57.9%) expanded achenes contained em-
bryos.Theseindicationsofreductioninfertilityarcsimilartothosefound
inthenaturalandartificialhybridsmentionedabove(Jackson 1966; Jack-
son& Dimas 1981; Lane 1980, 1983).
AsindicatedinTible 1,Harhnan&Punk4127hasyoungstems,pedun-
cles, capitula, involucres, and phyllaries like those ofX, humile, but
capitulescence,receptacles,achenes,andpappussimilarto/. vaieta. Inall
theotherfeatureslistedinTable 1 andshowninFigure3,thespecimenis
intermediatebetweenthetwotaxa(e.g.,habit,leaves,floretnumbers,fea-
turesof thestyle branchappendages, and achene lengths).
The most striking features ofthis plant arefound in the "ray" florets
(Fig. lA), which havedenselyvillous tubes, unusuallydeepsinuses, and
adaxialepidermalcells(Fig. IB)quiteunlikethoseofX.himiik(/.vemtais
eradiate)showninFigure IC.Theseflorets,unliketherayfloretsof"good"
taxaoftheAstercae,containstamens(althoughrudimentary)andthestyle-
branch appendages insomeofthe florets resemble moreclosely thoseof
diskflorets.Thesamephenomenaoccurinanothernaturalradiate-eradiatc
hybrid betweenMachaerantheramtiformisB. TurnerandM, gypsophilaB.
Turner (Turner & Sanderson 1971; Turner 1973). Theseanomalous "ray
florets"appeartobehighlymodifieddiskflorets(pers.obs.oftheauthors).
Jackson & Dimas (1981), who experimentally hybridized /. veneta with
Haplopappiisai/re/isA. Gray(aradiatespecieswithn — 6), foundthatthe
presenceorabsenceofrayfloretsisasingle-genecharacter(seealsoGottleib
198'1),althoughlengthofthelaminawhenrayfloretsarepresentisappar-
ently quantitatively inherited. Our observations suggest that length as
well asotherfeaturesofthe laminaarepolygenicallycontrolledand that
somegenesinvolvedindiskfloretstructurecanbe"turnedon"bytheallele
for presenceofray florets. These hypothesesawait testing.
Recently,GuyNesombroughttoMourattentiontwoadditionalputative
hybrids.Thefirst{G. CastilloC. & Vazquez3063,TEX)wascollected
in thesamearea (Mexico: Puebla: road from Zacatepec toElCarmen at
325
//
^^
\ ,y
1 mm
XiinFtIb(GK.'t'l^.>ihLiihinmehdiirmailwii:n{gLasnio'f2d3i9s'k>,flToEreXt)s,.sHh.owIhiinigimagtoibl&ctf-usnhakpqcdl2c7or(olRlMa)s.(sCt.aleIsibnaormaasreimndtiaca(tleida)r.lmAa.n
3H,U),TI-.X).AchenepubescenceofHartm,jn6r»nk-iU^andhitaimavemtaisnotshown,andonlya
fewofthepappusbristlesaredepicted.
326
borderwithTlaxcala, 12Jan 1984). Itagreesingeneralwiththedescrip-
tionofHartman &Funk4127 inmostmorphologicalfeaturesexcept the
leavesaresmaller, 10—20mmlong. Interestingly,theraycorollasexhibit
oneofthefollowingconditionswithrespecttotheadaxialpetals;bothare
suppressedasinanormalfloret,oneorbothispresentbutreducedinsize,
bothareunitedintoanarrowlamina1/2—4/5aslongastheabaxialone,or
oneorboth ispresentasalaterallobeoftheabaxiallamina. Thesecond
(1H4(.)H.kmlitWis.NA.WJosoef.t&heAs.iteL^fjo.rw/H,'a«rft8m0a2n;&TEFXu)nkwa4s12co7ll(eMcetxeidcaop:prMoexxiimcaot:eolny
T(daarh.mifr1.om(Crolimfpasrpiescoimneonl),Xi/annlldyH-lcu/i'lcho/mt/u/rn/-/iu/-jt/azm(/Ideat{al\mc.o\infpriolmedUmftr-om1H9a8l0l,1i9y<2S83)p,pH.ar2l2D^Uj—n2a2n4d,IJ'alocikks4on12&7
Dimas 198I,andpersonalohservarionntIL/r/im/n_)H_U)).
XiiNtbdcepthiliiinbumlie liiirtniiiil&l-nrik4127 Isiiidniiileiiela
HAiiir |irosrrare,|XTennialherb sjirawling,perennialherb shrub
YonNi,SriMS reddishtopurple,villous retldishtopur|ile,villous green,glabrousto
puberulcnt
Li:avi.s Imeantonarrowly lanceolateto oblanceoiateto
(CaIM'IarIlcl.l.iAn suosluoiathlaolrvyyareen-nsrpearulate 41——li83n,esaaprle-idleuannmtceutolelaeattthee/,siidne 42——sp85a,tsua±lliaetsneest-.sotiblelee,otnhig/nside
corymboseclusters corymboseclusters
Pini'NCl.KS villoLis,bracteate villous,bracteate pubescentbutnot
villous,ebractcare
InvHoii.iiuc.hrtis 4h.em3i^sp6h.e4rimcm h5e-mi6spmhemric b5r—oa8tllmymturbinate
WlDlH 5.7-6.9mm 7-9.5mm 4—6mm
FldllAKllS norresinou.s norresinous resinous
Ri(II'rA<i.i-.s renculate,.scalesnone alveolate,alveolae alveolate,alveolae
Rf\yI'YoRiIS 14—32,pistillate 12r—im1m5,edhebrymaspcharloesditic rimmedbyscales
(anthersrudimentary)
(.oKiii.i.A Tinis rnchomesglandular denselyvillous
anduniseriate
DiskI'lokits 29^46(80) 32-40 15-25(^0)
(.11l1.((i.)1N(1,,rAii 2.9 1.6mm 4—5.7mm 5—7mm
(.oKoiiA'I'liiiistrichomesglandular trichomcsglandularand glabrousortrichomcs
Si"!M-BrancII uniseriate sparse,uniseriate
AiM'iNDAi.is papillaeelongate, papillaeek^ngafc, papillaeshort,
attenuate rounded rounded
Aiiii-,Ni,; glabrous, sparselysilky-villous, denselysilky-villous,
1,1N(,111 1—go2k.-l1enmmbrown 1.t9a-nSmm 1.l8i-gh4tmtamn
PaI'I'IIS noneorlowscalycrown bristles bristles
1.1N(.Ill 1.5-4mm 3—6mm
P()MIN
SiAINAHllII'l 99.29? 51.4% 98%
327
WSW
formerbedofLagoTexcocoatkilometerpost7, ofTexcoco, 10Jan
1978). Itfitsclosely thedescriptionofHartman&Funk4127exceptthe
sphloarntteirs(otludbeera2n.5d—mo3stmomftlhoenpgu;bleasmciennace2.ha7s—be3enmmlostloanngd)tahnedraeyitchoerrolhlaasias
narrow,adaxiallammanearlyequallingtheabaxialoneorisnormalinthis
respect. Bothoftheseputativehybridswerefoundtohavedevelopedem-
bryosinonly 10%oftheexpandedachenes(1of10;limitednumberavail-
able). Pollenstainabilitywasalsomuchlowerinthesespecimensthanin
Hart?nan & Funk 5027] Castilloand Vasquez 3063 had 28.1% stainable
pollen(307of1090grainsobserved),andl/lisetal. 802only 13.9%(145
of 1042 grainsobserved).
Jackson's(1966)hypothesisthattaxaofAstereaehavinggoblet-shaped
disk corollas are related has certainly been supported by his and others'
more recent work, including thepresent paper. However, ifHaplopappus
pbyllocepbalus DC, H. annuus (Rydb.) Cory, and H. aureus (the
"phyllocephalus group" ofHartman 1976, 1990) were to be placed in
Isocofna(Haplopappussect. Isocoma sensuHall 1928) based on the hybrids
reported byJackson &c Dimas (1981), then Xanthocephalum sensu Lane
(1983) should also be accrued, based on the Xanthocephalum humile X
Isocoma{Haplopappus)venetahybridreportedhere.Therearestrongmorpho-
logicalandchloroplastDNArestrictionsitedata(D. Morgan,Y.Suh, B.
Simpson, M. Lane, unpubl. data)thatsuggestthatthemonotypicSteph-
anodoria (Robinson 1892) is very closely allied with Isocoma and
Xanthocephalum.Further,XanthocephalumisclearlyrelatedtoGrindelia(in-
cludingPrionopsis, Morgan, Suh, Simpson, Lane, unpubl. data)towhich
Olivaea(DeJong & Beaman 1963) is also allied (Lane 1982).
Althoughtheexperimentalandnaturalhybridsandotherdatadiscussed
herecertainly do indicate relationshipofthesetaxa, webelieve that the
"lumping" ofthe several genera, before the detailed morphological and
DNA-systematic investigations currently underway(Nesometal. 1990;
Lane,unpubl.data;Y. SuhandB. Simpson,pers. comm.)arecompleted,
would result inavery largegenus thatwouldbenotonlysystematically
uninformative butalsoanomenclatural nightmare. Ifall were joined to
Hall's (1928) Haplopappus (in which case the generic name would be
Xanthocephalumbasedonpriority)ashasbeensuggestedbysomeworkers,
thenitwouldfollowthatyetothergeneraofAstereaeshouldalsobeunited
withit. Ultimately,thecollapseofmostifnotallofthetribeintooneora
veryfewgenerawouldresult. Suchasituationwouldobscureratherthan
clarify the phylogeny of the Astereae; for this reason we continue to
recognize distinct genera, even though theirmembers may occasionally
hybridize.
328
ac:kn()wli;ixjMi<,nts
ThisstudywassupportedbyNSFgrantnumberBSR-8508631toMAL
andanOhioStateUniversityGraduateSchoolpostdoctoralfellowshipto
RLH during 1976—77, when theplantwascollected. We thank B. L.
Turnerfordiscussionoftheplant,R.C.Jackson,G.Nesom,J.L.Strother
and an anonymous reviewer for their comments on the manuscript,
J. Panerofortranslatingtheabstract,G.Nesomforbringingtoouratten-
tionthetwoadditionalhybrids,andV.A. Funkforassistanceinthefield.
rhi-i-ri:nc:i-s
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