PHYLOGENETIC RELATIONSHIPS WITHIN APIALES: EVIDENCE FROM WOOD ANATOMY

6 Pages·2001·0.33 MB·

by  Oskolski, A A

EDINB. J. BOT. 58(2):201–206(2001) 201
PHYLOGENETIC RELATIONSHIPS WITHIN
APIALES: EVIDENCE FROM WOOD ANATOMY
A. A. O*
WoodanatomicaldataconfirmthecloserelationshipsofmostAraliaceaetoApiaceae,
butdonotindicateanyintermediategroupsbetweenthetwofamilies.Heteromorpha
Cham.&Schltdl.,BupleurumL.andMelanoselinumHoffm.formawell-delimited
groupdistinguishedfromotherwoodyApiaceaebyhelicalthickeningsontheirvessel
walls,septatefibres,andmostlyhomogeneousrays.ThewoodinessinNirarathamnos
Balf.f.andMyrrhidendronJ.M.Coult.&Roseislikelytobeofsecondaryorigin.
Keywords. Apiaceae,Araliaceae,systematicwoodanatomy.
I
Although Araliaceae and Apiaceae (Umbelliferae) are commonly accepted as two
closelyrelatedtaxa,differentsuggestionsontheirphylogeneticrelationshipshavebeen
proposed.Traditionally,thetwofamilieshavebeenregardedastwoseparatelineages
thatarosefromacommonhypotheticalancestor.Thiswasbasedmostlyonmorpho-
logical and anatomical data (e.g. Rodriguez, 1971). Alternatively, Apiaceae has been
considered as an evolutionary successful group derived from within Araliaceae. This
view was supported by occurrence of taxa within Apiales (e.g. Myodocarpus Brongn.
& Gris., Apiopetalum Baill., Stilbocarpa (Hook.f.) Decne. & Planch., Hydrocotyle L.)
thatcombinesometraitsofbothAraliaceaeandApiaceaeandarethereforeregarded
asintermediatelinksbetweenthetwofamilies(e.g.Thorne,1973).Recentresultsfrom
morphologicalandbiogeographicalstudies(Lowry,1986a,b),andofcladisticanalyses
based on matK and rbcL sequence data (Plunkett et al., 1996a,b, 1997), suggest
howeverthatthemajorityoftaxainApialesfallintooneoftwowell-delimitedgroups
which correspond largely to Araliaceae or Apiaceae, whereas others belong to a
number of distinct ancient, paleotropical lineages (e.g. Myodocarpus, Delarbrea
Vieill.,Apiopetalum,MackinlayaHook.f).Theobjectiveofthisstudywastoexamine
these hypotheses on the basis of an analysis of wood-structure diversity.
W A  A
PublishedreferencesandoriginaldataonthewoodstructureofAraliaceae(170species
of 44 genera have been examined) have been summarized by Oskolski (1994, 1996),
Oskolskietal.(1997),andOskolski&Lowry(2000).Thisfamilydisplaysaconsiderable
range of wood diversity and specialization (sensu Bailey, 1951). For example, average
* Botanical Museum, Komarov Botanical Institute of the Russian Academy of Sciences, Prof. Popov
Str.2,197376StPetersburg,Russia.E-mail:[email protected]
202 A. A. OSKOLSKI
vesselelementlength,whichisanimportantindicatorofthelevelofxylemspecialization,
rangeswithinAraliaceaefrom370mminOplopanax(Torr.&A.Gray)Miq.to1370mm
inScheffleraJ.R.Forst.&G.Forst.,butinmostgenerathisparametervariesbetween
600–900mm. Perforation plate type varies from exclusively scalariform (up to 56 bars
in Osmoxylon Miq.) to exclusively simple (e.g. Aralia L., Tetraplasandra A. Gray).
Themostimportantdiagnosticwoodcharactersforthefamilyaretheaxialparen-
chymatype,theoccurrenceofseptatefibresand/orofradialcanals,andtheinterves-
sel pit size. Core Araliaceae (40 genera examined) share relatively large intervessel
pits,scantyparatrachealaxialparenchyma,andthepresenceofseptatefibres(which
canbesecondarilylost)andofradialcanals(Fig.1a,b)inthemostprimitivegenera.
Myodocarpus(Fig.1c,d),DelarbreaandPseudosciadiumBaill.formawell-delimited
assemblage,whichissharplydistinguishedfromotherAraliaceaebyrelativelysmall
intervesselpits,apotrachealdiffuse-inaggregatesaxialparenchyma,andalsobynon-
septatefibres(Oskolskietal.,1997).ApiopetalumandMackinlayacompriseanother
well-delimitedassemblage,characterizedbyrelativelysmallintervesselpits,presence
ofbothparatrachealandapotracheal(diffuseanddiffuse-in-aggregates)axialparen-
chyma, non-septate fibres, and absence of radial canals (Oskolski & Lowry, 2000).
W A  A
Shrubs or small trees occur in c.20 apiaceous genera (out of c.300 in this mostly
herbaceous family), representing all three traditionally recognized subfamilies
(HydrocotyloideaeLink,SaniculoideaeBurnettandApioideaeDrude).Woodanatom-
ical study of 10 species in nine genera (Arracacia DC., Bupleurum L., Eryngium L.,
HeteromorphaCham.&Schltdl.,MelanoselinumHoffm.,MyrrhidendronJ.M.Coult.
&Rose,NirarathamnosBalf.f.,PlatysaceBungeandSteganotaeniaHoscht.)hasadded
to data published by Metcalfe & Chalk (1950) and Schweingruber (1990), but
Rodriguez(1957)remainsthemostimportantandextensivedatasourceonthefamily.
WoodyApiaceae(exceptsomehydrocotyloidswithanomalousstemstructure,e.g.
Azorella Lam.) resemble core Araliaceae in their wood structure, but differ by their
distinctlyshortervesselelements(averagelengthfrom240mminEryngiumto500mm
inHeteromorpha,butRodriguez,1957,notedthatinthehydrocotyloidsAsteriscium
Cham. & Schltdl., Gymnophyton Clos and Trachymene Rudge, this parameter
varies from 170–240mm), and also by exclusively simple perforation plates. Wood
FIG. 1. Wood structure in some Araliaceae. Scale bar=100mm. a, b, Aralia soratensis
Marchal(=PentapanaxangelicifoliusGriseb.):Argentina,Kw10714.Anexampleofthetypi-
cal wood structure for the core Araliaceae; a, trans-section – thin-walled libriform fibres,
scantyparatrachealaxialparenchyma;b,tangentialsection–septatelibriformfibres,hetero-
geneous rays of Kribs’ IIB type, radial canal. c, d, Myodocarpus fraxinifolius Dubard & R.
Vig.;NewCaledonia,Lowry3679;c,trans-section–thick-walledlibriformfibres,apotracheal
(diffuse-in-aggregates) axial parenchyma; d, tangential section – non-septate libriform fibres,
homogeneousrays,radialcanal.
WOOD ANATOMY AND PHYLOGENY WITHIN APIALES 203
a b
c d
204 A. A. OSKOLSKI
anatomical data confirm the close relationships of core Araliaceae to Apiaceae, but
do not support ideas of linear phylogenetic sequence of the two families because no
intermediate groups have been identified. Myodocarpus, Delarbrea and
Pseudosciadium,aswellasApiopetalumandMackinlaya,oftenregardedas‘bridging
taxa’ between the families, differ distinctly from both core Araliaceae and Apiaceae.
Instead, wood anatomical data support the view (Lowry, 1986a,b; Plunkett et al.,
1996a,b, 1997) that these assemblages are separate, isolated lineages.
WithinApiaceae,Apioideaearecharacterizedbylessadvanced(sensuBailey,1951)
wood structurethan Hydrocotyloideaeand Saniculoideae,as indicatedby thelonger
lengthoftheirvesselelements.However,relationshipswithinthesethreesubfamilies
remainobscureforwoodanatomists.Awoodyhabitappearstohavearisensecond-
arilyfromherbaceousancestorsinseveralApiaceaegenerasuchasthehydrocotyloids
Asteriscium, Azorella and Mulinum Pers. (Rodriguez, 1957), and the apioids
NirarathamnosandprobablyMyrrhidendron(Downieetal.,1998).Secondarywoodi-
ness in these taxa can be recognized by an anomalous stem structure, as in Azorella
(Rodriguez, 1957) or by such paedomorphic wood features (sensu Carlquist, 1962)
as the combination of simple perforation plates, scalariform intervessel pitting, and
apredominanceofuprightandsquarecellsinraycomposition,andalsothetendency
to raylessness in Myrrhidendron (Fig.2c,d).
Three apioid genera, Heteromorpha, Bupleurum and Melanoselinum, form a well-
delimitedgroupdistinguishedfromotherwoodyApiaceaebyhavinghelicalthicken-
ings on their vessel walls, septate fibres, and mostly homogeneous rays (Fig.2a,b).
The presence of septate fibres links these genera to Araliaceae, where this character
is very common; no Araliaceae can, however, be regarded as their close relatives.
Available data therefore confirm Drude’s (1898) idea of close relationships among
thesethreegenera,aswellastheview(Plunkettetal.,1996a,b;Downieetal.,1998)
on their basal position in the Apioideae clade.
A
This research was supported by a stipend from the German Academic Exchange
Service(DAAD);fieldworkinNewCaledoniaandAustraliawassupportedbyNGS
grant 5793-96. I sincerely thank P. P. Lowry II and G. M. Plunkett for helpful
collaboration, and P. Baas, M. Gregory, P. Gasson, B. J. H. ter Welle for their
FIG. 2. WoodstructureinsomewoodyApiaceae(subfam.Apioideae).Scalebar=100mm.
a, b, Heteromorpha arborescens Cham. & Schltdl., Tanzania, Kw 10606; a, trans-section –
thin-walled libriform fibres, scanty paratracheal axial parenchyma; b, tangential section –
alternate intervessel pitting, helical thickenings on the vessel walls (arrow), septate libriform
fibres, uni- and 2-seriate homogeneous rays. c, d, Myrrhidendron pennellii J. M. Coult. &
Rose:Columbia,Uw20765;c,trans-section–thin-walledlibriformfibres,scantyparatracheal
axial parenchyma, rays poorly distinguished; d, tangential section – scalariform intervessel
pitting,non-septatelibriformfibres,rayscomposedofuprightcells(tendencytoraylessness).
WOOD ANATOMY AND PHYLOGENY WITHIN APIALES 205
a b
c d
help in obtaining wood samples. I am also very grateful to E. S. Chavchavadze,
H. G. Richter, E. John, J. West, B. Hyland, B. Gray, R. Jensen. Assistance was
provided by the Botanical Museum, the V. L. Komarov Botanical Institute,
206 A. A. OSKOLSKI
St Petersburg; the Ordinariat fu¨r Holzbiologie, Universita¨t Hamburg;
Bundesforschungsanstalt fu¨r Holz- und Forstwirtschaft, Hamburg.
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Received20January2000;acceptedwithrevision1June2000