Table Of ContentComp. Newsl.34, 1999 53
Reclassification ofPrenanthespendula
(Asteraceae: Lactuceae)
&
AlexanderN.Sennikov IreneD. Illarionova
Herbarium
KomarovBotanicalInstitute
Prof.Popovstr.2
SaintPetersburg,197376Russia
e-mail:[email protected]
Abstract
The species with uncertain taxonomic position, Prenanthespendula Sch. Bip., was
studiedinrespectofmorphology,anatomyandsurfaceultrasculptureofachenes.The
structureofitspericarpissimilartothatinspeciesofSonchussubgen.Dendrosonchus
towhichthisspeciesistobeattributed.
Introduction
The taxonomic position ofP. pendula, endemic to the Canary Islands, has always
been unclear. First described as a member ofthe genus Prenanthes (Webb & Ber
THELOT 1842-1850), this species remains static in the Lactuceae (Cichorieae), even
though theprotologue ofthis name includes theremark by P. Webb on its possible
relationshiptoSonchus:"Sonchus(Picrosonchus)pendulusWebb,inUtt."(1.c:421).
ThischaracteristicspeciesistheonlymemberofPrenanthesfromtheCanaryIslands,
inhabitingmountaincliffsonGranCanaria(Bramwell&Bramwell 1974).Thisspe-
cies is characterized by a woody basal stem, pinnatisectleaves with large triangular
lobes,corymboseinflorescencewithsmallcalathidiaof5-6florets(each),smooth,4-
5-striateachenes and thin white subglabroussubmonomorphic pappus setules. Con-
sideringits special habit, P.pendula israthersimilartoCanarian species ofSonchus
sect. Atalanthus (D. Don) DC. (syn. Taeckholmia Boulos) and S. tuberifer Svent.
(sect. TuberiferiBoulos).
In recent years doubt was thrown upon the former position of P. pendula. Some
morphologicalandbiologicaldata(PerezdePaz 1976)faciUtatedthesuggestionthat
P. pendula is closely related to Sonchus and Sventenia (small monotypic segregate
closetoSonchus).AnaturallyoccurringhybridbetweenSventeniabupleuroides Font
54 Comp. Newsl. 34, 1999
QuER and P. pendula was reported by Sventenius (1960). The relationships drawn
fromtheresultsofthestudyofsequencesfromtheinternaltranscribedspacerregion
of nuclear ribosomal DNA (Kim et al. 1996) connect P. pendula with Sventenia,
Babcockiaplatylepis (Webb) Boulos (=SonchusplatylepisWebb) as wellas S. sect.
Tuberiferi, S. subgenusDendrosonchus, andTaeckholmia.Tofurtherclarifytheposi-
tion ofP. pendula, we have undertaken studies of morphology and anatomy ofits
fruits. Carpologicalmethodiswell-establishedinsystematicsofAsteraceae(cf.Lavi-
alle 1912, and forexample, Pak & Kawano 1990 a, b), and usually provides good
resultsinstudiesonLactuceae.
MaterialsandMethods
The achenes ofP.pendula were studiedin respectofmorphology, anatomy andsur-
faceultrasculpture.Theachenesweretakenfromherbariumspecimen,thesyntypeof
P.pendula: "InmontibusCanariae,Webb"(LE).
Theachenes weretreatedin an alcohol-glycerine-watersolution(1:1:1)duringthree
daysandcutwithfreezingmicrotomethroughtheirmiddle(throughcotyledons)and
basal parts. Sections were made at a thickness of 10-16 m|i; prepared slices were
colouredwithsafranin.DrawingsweremadewithdrawingdeviceRA-7bythesecond
author. Surface ultrasculpture was studied with scanning electron microscope JSM-
35C.
MorphologicalandAnatomicalData
Fruit
mm mm
The mature achenes oiP. pendula are homomorphic, 4-^.5 long., 1.1-1.2
wide, stramineous, cylindrical, broadly conical atthe base and rounded atthe apex,
mm
round in cross section, smooth, 4-5-striate with furrows (Fig. 1). Pappus 2.5-3
long, uniseriate or partly biseriate, subhomomorphic. Pappus setules are 0.02-0.03
mm
thick, most of them are thin with few slightly thickened ones, white, slightly
denticulate,ratherfragile, slender.
Pericarp
Crosssectionofmatureachenesshowsmoreorlessroundoutline(Fig.2).Thepericarp
is80-100m\xinthickness.Thelayoutoftheacheneis4-5-merous(fromachenesin
thesamecalathidium).Pericarpisclearlydividedinsectioninto4-5lobeswithnarrow
furrows. Itiscomposedbyexocarpandwelldifferentiatedmesocarp.Eachmesocarp
Comp. Newsl.34, 1999 55
lobecontainsthreestrandsofsclereids, whichareseparate,roundandnearlyequalin
thebaseofachene,andfusedintotrilobedbandinthecenteroftheachene.Thisband
ishomogeneous,consistingof10-12layersofstrandsandof(1) 3-4layersbetween
them, underlain by obhterated parenchyma cells (Fig. 3). One or two layers ofthe
elongated sclerified parenchyma with prominent pores in die walls overlay the
sclerenchymabandsandconvergebetweenthem.Exocarpconsistsofasinglelayerof
epidermictissue.Theepidermiccells arerathernarrow,4-6mjahigh, 8-12m|awide,
cuticularized, withconcaveupperwalls.
SeedCoat
Therearesomerowsoftheseedcoatcellsobliterated,beingpresentascellwallsonly.
Endosperm
Theendospermistwo-layered,consistingofthin-walledcellswithgrainedsubstance
within.
The study ofultrasculpture ofachene surface shows theepidermic cells to berather
narrow, 50-120m|jlong, 8-12m|awide, elongated inaxialdirection, withoutapical
outgrovk^s (Fig. 4). The cell surface is shghtly rugose, without prominent cuticle
structures.
Discussion
Analysisofmorphologicalandanatomicaldata providesmoreevidenceinfavourof
the inclusion ofP. pendula into the subtribe Sonchinae K. Bremer (Bremer 1993,
1994), rather than keeping it within Prenanthes. All species of Sonchinae possess
acheneswithpericarpdividedinsectioninto4-5lobeswithratherprominent(atleast
atthebaseofachenes)furrows,complementedwithsoftorslender,heteromorphicor
subhomomorphicpappussetules(Sennkov &Illarionova,inpress)whereasspecies
oiPrenanthes (Sennkov 1997, in press) have achenes without furrows, with hard,
homomorphicpappussetules (Sennkov &Illarionova, inpress). Plantmorphology
allowsustosuggestP.pendulabecomparedwithS. tuberiferbyitspinnatisectleaves
withlargelobes, aswellaswith5. sect.Atalanthusbysmallcalathidia, inflorescence
shapeandbasallywoodystem.JudgingbythemostdistinguishingfeatureinLactuceae,
S.platylepis(sect. Bahcockia(Boulos)Sennk.)isthespeciesmostcloselysimilarto
P.pendulabythestructureofitsachenes.Theachenesof5.platylepishave4pericarp
lobeswithoutribs (Webb &BERXHELOt 1842-1850); every lobepossesses5 subequal
sclerenchymatousstrands(Aldridge1976).Inouropinion,P. pendulaischaracterized
56 Comp. Newsl.34, 1999
byaratherprimitiveachenestructureofSonchus-type.,becausethepericarpiumisnot
differentiated into ribs though the number of sclerenchymatous strands is reduced
from5 (primarily) to 3 (as inS. leptocephalusCass, from sect.Atalanthus), and the
strandsarepartlyfused.Thus,thisspeciessharesthemostimportantfeaturesofsome
species ofsubgen.Dendrosonchusandmay belongthere.We supporttheopinionto
unitesomesegregatesclosetoSonchuswithSonchuss.str.intoasinglegenusaccording
tomorphological and anatomical features, andtotreatthesubgenusDendrosonchus
& &
in broader sense (Webb Berthelot 1842-1850, Aldridge 1976, Redfenberger
Reefenberger 1996). To this treatment, P. pendula should be placed into subgen.
Dendrosonchus, forming asectionofitsown.
NomenclaturalConclusions
Sonchus sect. Chrysoprenanthes (Sch. Bip.)Sennk.,comb,nov.
Basionym: Prenanthessubgen. ChrysoprenanthesSch. Bip. inWebbetBerth.,
Hist. Nat. liesCanar. 3, 2,2: 420(1849).
Type: Prenanthespendula Sch. Bep. (=Sonchuspendulus(Sen. Bep.) Sennk.).
5.pendulus(Sch. Bep.)Sennik., comb.nov.
Basionym: Prenanthespendula Sch. Bip. inWebb etBerth.,Hist.Nat. lies
Canar. 3, 2, 2: 421 (1849).-Syntype: "InmontibusCanariae,Webb"(LE!).
References
ALDRmoE, A. E. 1976. Anatomy and evolution in the Macaronesian Sonchus sub-
genus Dendrosonchus (Compositae: Lactuceae). Bot. Joum. Linn. Soc. 76 (4):
349-285.
Bramwell, D. & Z. Bramwell 1974. Wildflowers ofthe CanaryIslands. Stanley
Thornes (Publishers)Ltd., London.
Bremer,K. 1993. NewsubtribesoftheLactuceae(Asteraceae). Novon3: 328-330.
Bremer,K. 1994.Asteraceae: CladisticsandClassification.TimberPress,Portland,
Oregon.
Kim,S.-C,Crawford,D.J.&R.K.Jansen 1996.Phylogeneticrelationshipsamong
thegeneraofthesubtribeSonchinae(Asteraceae): EvidencefromITSsequences.
Syst. Bot. 21 (3): 417-432.
Lavialle, p. 1912. Recherches sur le developpement de I'ovaire en fruit chez les
Composees.Ann. Sci. Nat. (Paris). Ser. 9, 15: 39-149.
Comp. Newsl.34, 1999 57
Pak,J.-H.&S.Kawano1990a.BiosystematicstudiesonthegenusIxeris(Compositae
-Lactuceae), I. Fruitwallanatomyanditstaxonomicimplications.Ac/aP/zy/o/ox.
Geobot. 41 (1-3): 43-60.
Pak, J.-H. & S. Kawano 1990 b. Biosystematic studies on the genus Ixeris and its
alliedgenera(Compositae-Lactuceae), IE. Fruitwall anatomy andkaryologyof
Crepidiastrum and Pamixeris, and their taxonomic implications. Acta Phytotax.
Geobot. 41 (3-6): 109-128.
Perez de Paz, J. 1976. Observaciones sobre la biologia y relaciones de Sventenia
bupleuroidesF. Q.BotanicaMacaronesica 1: 51-65.
&
Rebfenberger,U. A. Reifenberger 1996.Vereinigung derGattung Taeckholmia
BouLX)SmitderGattungSonchusL. (Compositae)undEmendationdesSubgenus
DendrosonchusSch. Bip. FeddesRepert. 107(5-6): 311-319.
Sennikov,a. N. 1997. The species of the genera Prenanthes and Cicerbita group
(Asteraceae)intheCaucasus.Bot.J.(St.Petersburg)82(2): 106-114(inRussian).
Sennikov, A. N. (in press). De generibus ex affinitate Prenanthes L. (Asteraceae).
Novit. Syst. PL Vase. (St. Petersburg) (in Russian).
Sennikov,A.N.&I.D.Illarionova(inpress).Morphologicalandanatomicalstructure
ofachenesinthegenusSonchuss.1.(Asteraceae).Bot.J. (St.Petersburg)(inRuss-
ian).
SvENTENius,E. R. S. 1960.Additamentumadfloramcanariensem. Madrid, Spain.
Webb,P. &S.Berthelot 1842-1850.HistoirenaturelledesliesCanaries. 3(2,sect.
R
2): 1-496, 37-136b.
58 Comp.Newsl.34, 1999
Fig. 1. AnacheneofP.pendula (SEM micrograph), x20.
Comp.Newsl.34, 1999 59
A
B
mm
0.5
Fig. 2. Simplified cross section ofachene ofP. pendula. A: at the base part ofthe
achene. B: at the middle part of the achene. Sclerenchyma tissue is crossed.
60 Comp. Newsl.34, 1999
Fig. 3. Partofcross section ofmature achene ofP. pendula with anatomical details.
I-pericarp;H-seedcoatobliterated;IE-endosperm.Cuticleofepidermiccells(C);
epidermal cells of pericarp (EP); sclerified elongated parenchyma (SP);
sclerenchymatouscellsofpericarp(SC).
Comp. Newsl. 34, 1999 61
Fig. 4. StructureofachenesurfaceofP.pendula (SEMmicrograph), x200.
