The genera Mitchella and Damnacanthus. Evidence for their close alliance; comments on the campylotropy in the Rubiaceae and the circumscription of the Morindeae

39 Pages·1991·9.1 MB·English

by  Robbrecht, E

BLUMEA 35 (1991) 307-345
The genera Mitchellaand Damnacanthus.
Evidence fortheir closealliance; commentsonthecampylotropy inthe
Rubiaceaeandthecircumscription oftheMorindeae
E. RobbrechtC. Puff & A. Igersheim
Summary
The two species ofMitchella (SoutheastAsian andNorth American) and several species ofthe
SoutheastAsian genusDamnacanthusare investigated.Vegetativecharacter states (growthform,
branchingpattern,leaves)ofthetwo genera aredescribed andcompared.Damnacanthusalways ex-
hibits heterophylly and somespecies havepairedthorns. The latterare interpretedaspairedlateral
shoots in theproximal part ofasympodialbranch unit,and itis speculatedthatthepairedthorns
maybe modified inflorescence shoots.
Detailed information is alsogivenoninflorescence structure and floral morphologicaland ana-
tomical details ofDamnacanthus and Mitchella. Particular emphasis isplaced ontheovaries, the
structureofwhich isremarkablysimilarin the two genera.The uniovulate loculesarecharacterized
by havingcampylotropousovuleswhich areinsertednearthetopofthe septum;extensiveobturator
tissue coverspart ofthe horizontallyarrangedcurvedovule incap-like manner.The micropyleofthe
ovule,obscured bytheobturator,points upwardsandto some degreealso inwards,while theembryo
sac is foundin a±horizontal position. The seeds,however, contain minute embryos, ofwhich the
radicles arepointing±downwards. This apparentlycontradictingmicropyleandradicle positionfinds
itsexplanationin the unusual ovule structure and orientation and in the subsequentstrong growth
oftheendosperm,throughwhich theembryoispushedto theposition whereitis found in mature
seeds. The detailed structure ofthedrupaceousfruitsand ofthe seedsofboth generaare compared.
Chromosome numbers (x =n=11,2n =22)arepresentedforMitchella andDamnacanthus,cer-
tain palynologicalinformation isadded,andliterature onreproductivebiologicalaspects isreviewed
and supplementedbyoriginalobservations.
WhileMitchella hadbeen associatedwith variousdifferent tribes,Damnacanthus wasin thepast
nearlyalwaysplacedinthe Morindeae. Theinvestigatedcharactersoverwhelminglysupportthe close
alliance between Mitchella andDamnacanthus. However,according toourpresent state ofknowl-
edge,the Morindeae appear tobe aheterogeneoustribe,and atleastagroupofgenera alliedtoPris-
matomeris isprobablyto be removed. Damnacanthus and Mitchella doshow certain agreements
with the‘core’ ofthe Morindeae,buttheirdefinite tribalplacementshouldbe withheld until arecir-
cumscriptionofthe Morindeae becomes available.
1. Introduction
ThetribalpositionofMitchellaL. was debatedfor along time.Dueto contradic-
tory and, in part, erroneous characterdescriptions inearly literature,the genus was
subsequently associated with various differenttribes. Ironically, Baillon's over-
looked and forgotten paper "Surdesradiculesd'embryon a directionanormale"had
'1 Nationale Plantcntuin vanBelgie,Domein vanBouchout,B-1860 Meise,Belgium.
2) InstituteofBotany,UniversityofVienna,Rennweg14,A-1030Vienna,Austria.
308 BLUMEA VOL. 35, No. 2, 1991
already provided convincing evidenceforthegenus' taxonomicposition. Baillonhad
clearly linkedtheproblemofMitchella’splacementwiththeapparently contradictory
micropyle andradicleorientationinMitchella.He (Baillon, 1879, 1880), moreover,
hadconsideredthegenusDamnacanthusGaertn.f. tobe closely alliedto Mitchella
andplaced bothinhis "serie desChiococca.” In morerecent publications, thegenus
Damnacanthusis generally foundincludedinthetribeMorindeae, andthereis virtu-
ally noreference to apossible alliancebetween MitchellaandDamnacanthus(see
chapter 5 forfurtherinformation). Although certain detailedstudies exist on repre-
sentatives ofboth genera,in-depth investigations of numerous important character
states are stilllacking. Up to now, neitherBaillon's(1879) findings regarding ovule
andseedstructure nor hisoriginally suggested close alliancebetweenthetwo genera
were ever checkedfor theircorrectness.
As goodpreserved materialofDamnacanthusspecies andthetwo species ofMit-
chellabecameavailablerecently, itwas possible to carryoutcomprehensive compa-
rative work onthetwo genera.
2. MATERIAL
InadditiontofieldobservationsonJapanese DamnacanthusandMitchellaspecies
(C.P.), herbariummaterialofthe following institutionswas studied:BKF, BR, L,
MAK,TI, W, WU.
Thefollowing material(* =preserved) was used for detailedinvestigations and
thepreparation ofthefigures:
Damnacanthusbiflorus (Rehd.) Masamune: Japan, Ryukyu Is., Tokuno-shima,
between BomaandNishiagina, Hatusima 19357(L) (fig. 3B); Amomio-shima, Chi-
nase, NaseCity, Fukuoka 8003(L).
DamnacanthusindicusGaertn.f.:India,Assam, KhasiHills, ThakurRup Chand
7403 (L).
Damnacanthus indicus Gaertn.f. subsp. indicus var. indicus: Japan, Shikoku,
Kochi Pref.,Taisho-Yuzuhararoad, aroundNiidashrine, Puff880508-1II* (WU)
(voucher for chromosomecount; figs. 2, 5B, 6C& D, 7, 8F& G, 13D).
Damnacanthus indicus Gaertn.f. subsp. major(Sieb. & Zucc.) Yamazaki var.
major: Japan, Honshu, Aichi Pref., Mikawa Prov., AtsumiPeninsula, Irako-zaki,
Jan. 22, 1968, Kanai & Ohashi s.n. (BR) (figs. 11A-D, 12B).
Damnacanthusmacrophyllus Sieb.ex Miq.formagiganteus (Makino) Yamazaki:
Japan, Shikoku, Kochi Pref., Taisho-Yuzuhararoad, around Niida shrine, Puff
880508-1/2*(WU) (figs. 4, 5A, 6A& B, 8A-E, 14E).
Damnacanthusokinawensis Hatusima (=Damnacanthusbiflorus x D. indicus
subsp. major): Japan, Ryukyu Is., OkinawaIs., Benoki-Yama, Sonoharaetal.SIRI
71701 (L) (fig. 3A).
Mitchella repens L.: U.S.A., Michigan, fruits fromWJ. Beal Botanic Garden,
Michigan State Univ.(figs. 11M-0, 12D& E, 13A& B).
MitchellaundulataSieb.& Zucc.: Japan, Shikoku, Kochi Pref., YokokuraMt,
Pufff880507-111* (WU)(voucher for chromosomecount); Honshu, TottoriPref.,
E.Robbrecht,C.Puff& A.Igersheim: The genera Mitchella and Damnacanthus 309
MtDaisen,Oct. 16, 1988,Suzuki s.n* (WU) (fig. 1IE); Meyer etal. 16894(MAK)
(figs. 11F-L,12A&C); Tokyo Pref.,Hachiioji-City, MtImakuma, June 30,1989&
July 18,1989,Suzukis.n.* (WU)(figs.6E & H, 9A& B, D& G, 13C, 14A-D);
Hokkaido, Mt Ashibetu, Aug. 2, 1988, Suzuki s.n* (WU) (figs. 6F & G, 9C).
3. METHODS
Chromosomecounts wereobtainedfromacetocarmine squashes ofvegetative ma-
terialorflowerbudspreserved inthefieldin3 parts ethanoland 1 part glacial acetic
acid. Materialpreserved in thefieldin70% ethanolwas used for both microtome
sections and, aftercritical-point drying, formost SEM-graphs. For other standard
methodsemployed see Robbrecht(1988).
4. COMPARISONS OF THE CHARACTER STATES OF
DAMNACANTHUS AND MITCHELLA
4.1. Vegetative characteristics
4.1.1. Growthform, branching pattern, and the thorns ofDamnacanthus (fig. 1)
Mitchellaspecies are perennial herbswith evergreenleaveswhosestems maybe
slightly woody at the base(hence Holm, 1907, prefers the term 'undershrub'for
Mitchellarepens). Plants tendto havea"strongly clumped spatial dispersion. This
distributionpatternresults fromthetendency oftheseprostrate perennials to spread
byproduction oftrailing stemswithadventitiousroots"(Hicks et al., 1985).
PlantsofMitchellaproduceratherlongunbranchedprimary shoots, besetwith leaf
pairs whichareallofthesame shape and± thesamesize ("The shootsofMitchella
[repens] ... appeartobe somewhatuniform, sincetheirfoliage is identical": Holm,
1907: 168). Lateralbranches originate on olderparts ofthese shoots, whichmay be
solitary or paired atanode.Lateralbranchesmay, in turn,produce lateralbranches
ofa higherorder. Primarily the basal shoot portions, i.e. thosein contact with the
substrate, oftendevelop adventitiousroots.
Thelateralbranch system ofamain axis mustnotbe confusedwith thesympo-
dial-dichasialor -monochasialbranching patternofthemainelements(in thecaseof
sympodial-dichasial branching, aslightly anisotomous development is usually rec-
ognizable, seefig. 1A). The materialavailableto us didnot provide conclusiveevi-
dencewhethersympodial branching is always forcedby theproduction of aterminal
inflorescenceor whetheritcanalsobe dueto terminationofmainaxis growth with-
outinflorescenceformation.The situationbecomes furthercomplicated andsome-
timesratherconfusing by inflorescencesproduced terminally on lateralbranches of
varying orders.
There is,thus, noregular sympodial-di- or monochasialbranching pattern with±
identicalrepeated sympodial elementsas inDamnacanthus(see below).
Damnacanthusis ashrubby genuswith conspicuously heterophyllous evergreen
leaves.Several species arecharacterizedby being armedwithpaired thorns(fig. 2A-
310 BLUMEA VOL. 35,No. 2, 1991
Fig. 1.Schematic representationofthe growthformand inflorescenceposition ofMitchella (A-B’)
andDamnacanthusindicus(C-E).- A:threeshootgenerations(I,II,III), twowithlateralbranches
(LI1,LIII1 ...); both lateral branches and sympodialbranch units bearterminal inflorescences (IF);
arrowspointtoposition ofnolongerexisting (old)inflorescences andmark thebeginningofasym-
podial-dichasialbranching;noteinflorescencesbeingovertoppedbyanew generationofshoots(IV)
and adventitiousroots in thenodal areas ofthe oldestpart oftheplant. - B: pairedflowers(1, 1’)
borneterminallyonaxisI;adevelopingshoot is shown in theaxil ofone ofthe foliageleaves(f).-
B’:groundplan ofB;notethatthepaired,fusedflowersarearrangedin rightanglestothe median of
the foliageleaves andare believed tohaveoriginatedfromanode withoutbracts (dottedcircle). - C:
heterophyllous branch consisting ofseveral shoot generations(I-V); note thatbranchingmay be
sympodial-dichasialor -monochasial. - D: sympodialbranch unit comprised ofapair ofprophylls
(p) and apairoffoliageleaves (f); nobracts arepresentbelow thepairofthorns(th),i.e. atthe third
node;i1, i2, i3, internodes;sa,shootapex;shown in black: the next sympodialbranch units (II). -
D’: groundplan ofD; thedotted circlerepresentsthe thirdnode withoutbracts. - E:anew vegeta-
tive (II)and afertile,2-flowered sympodialbranch unitarisingfrom theaxilsofthefoliageleavesof
asympodialbranch unit(comparewithD). - Furtherexplanationsin the text.
E.Robbrecht,C.Puff& A.Igershcim: The genera Mitchella and Damnacanlhus 311
D; in literaturefrequently referredto as spines. Sincethey are, as will beexplained
below, modifiedshoots, themorphologically more accurate term thornis usedhere).
Thethornsmay be very conspicuous and to c. 2 cm long orveryrudimentary and
hardly detectable.There are, however, also thornless Damnacanthusspecies (see
Chao, 1978; Yamazaki, 1987b). Presumably, they representthe end point ofa re-
ductionseries, i.e.thorns arereducedto such an extent thatthey are no longer dis-
cernible.Damnacanthusmacrophyllus, investigated by usin detail,forexample, had
withoutexception clearly detectablealthough very minutethorns (fig. 4); the spe-
ciesis describedas having "brancheswithoutor withvery shortspines" (Yamazaki,
1987b).
ThethornsofDamnacanthusare always associatedwithpairs oftrue('large') fo-
liage leaves.Theirorientationisalways inright angles tothepair offoliage leaves,
andthey are seemingly foundin the axilofoneoftheleaves, orin themiddlebe-
tween two lateralbranches andin the axilsofthe stipules (fig. 1C, 2B-D). There
have been various morphological interpretations of these paired thorns, none of
whichare, inouropinion, correct:
Schumann(1891: 137) describes them as follows (translated): "The thorns are
withoutdoubt... homologous tolateralbranches. In driedmaterialthey are foundin
frontof[i.e.,in thesame planeas] thestipules,thus they belong totheotherwise so
rare stipular shoots['Stipularsprosse']"; he,however,maynot have been fully satis-
fiedwithhisinterpretation as hesuggests thatthecorrectnessoftheproposed homol-
ogyshouldbetestedby ontogenetical investigations offreshmaterial.
Johansson(1987a: 147) describesDamnacanthusindicus as having "narrowstip-
uleswhich develop intospines". Thisinterpretation is totally unrealisticas thepair
ofleavesassociatedwith thepaired thornshas normally developed stipules (seefig.
2F). Johansson unknowingly followed A.P. & A. DeCandolle's(1833: 584) inter-
pretation:"...ces stipules sont remplaces pardesepines solitaires ..."(asBaumannia
geminiflora).
Kumazawa(1979: fig. 11.8) also assertsthatthe thomofDamnacanthusshould
beinterpreted asa metamorphosis ofthe leaf,and comparesthesituationwiththatin
Carissa(Apocynaceae). Forbothgenera,his interpretations are very likely tobein-
correct (see below).
Yamazaki (1987a) considers thethomtobe a metamorphosed lateralbranch; his
interpretation is, however, difficultto follow. Hetalks ofthe thorn being "trans-
formedfromthecompound ofthe lateralbranchandthecover leaf'[= bract?] ... and
"thegreaterpartofthespine"being "constitutedbythelateralbranchandthesmaller
partby thecover leafbeing completely adheredto thebaseofthelateralbranch."It
seems thathehasnot fully understoodthe general growthpatternandhow theposi-
tionofthepairedthornscanbeaccommodatedinthispattern.
Ourexplanation isas follows (fig. 1C & D', abbreviationsalso used inthetext
below):
InDamnacanthus, averyregular sympodial branching patternprevails (branching
is eithersympodial-monochasial orsympodial-dichasial - andthenoftenslightly ani-
sotomous). The entire shootsystem is comprised ofidenticalsympodial elements.
Eachsuchelementis comprised of:
312 BLUMEA VOL. 35, No. 2, 1991
E.Robbrecht,C.Puff& A.Igersheim: The genera Mitchella and Damnacanthus 313
1) apair ofsmall leaf-like or± scale-likeprophylls (p; i.e., the first leafpair ofa
sympodial element),
2) apairof(larger) foliage leaves(f). Each such leafmorphologically alwaysrepre-
sents abract ('Tragblatt') inwhoseaxil anew sympodial element(II) originates
(also seefig. 2C: bud), and
3) a pair ofthorns (th; which may,however, be reducedto varying degrees). The
paired thornsrepresentpaired lateralbranches(which are not supported by bracts)
intheproximal pordonofasympodial elementwhichceases growth immediately
afterthe production ofthethorns.
The structure ofsuch asympodial unitisobscuredby the factthattheaxis above
thepair offoliage leaves (i.e. the uppermostorthirdinternodeofa unit; i3) is ex-
tremely congested. Consequently, thepaired thorns seemto be directly associated
withthenodebearing thefoliage leaves.
Ourinterpretation ofthebranching pattern andthornofDamnacanthusthusfully
corresponds tothesituationinCarissa(Apocynaceae) as outlinedby Shah & Vasu-
devaRao(1977), except thatthepaired thornsofCarissa are subtendedby a pairof
scale-likeleaves, whereasthose ofDamnacanthusare not supported by bracts.
As thevegetative thorn-bearing sympodial unitis comparable to asympodial unit
bearing a2-flowered inflorescence(see paragraph 4.2for details),it maybespecu-
latedthatthepaired thorns are modifiedinflorescence shoots.Anargumentinfavour
ofthis speculation maybethat thepaired thornsoriginate atanode withoutbracts,
asituationthatisrepeated intheinflorescences ofDamnacanthus(see therefor de-
tails). Similarmodificationsofinflorescence structures are alsoknown fromsome
otherRubiaceae,e.g. Uncaria (Cinchoneae-Mitragyninae; climbing hooks=inflor-
escence peduncle, Guillaumin, 1931), or Catesbaeaspinosa (Catesbaeeae; paired
axillary thorns = pedicels ofsolitary flowers, Robbrecht, 1988: fig. 4A). Also for
Carissa (Apocynaceae; see above!), it has been argued that thorny branchesare
homologous toinflorescences (Brunard, 1970; Cohen&Arzee, 1980).
4.1.2.Roots
Peculiarmoniliformroots areknown fromDamnacanthusmacrophyllus (seere-
produced historicalillustrationsin Yamazaki, 1987b). Thisis apparently unique in
Fig. 2.Damnacanthus indicus subsp.indicus. - A: partofplantshowingseveral sympodial-mono-
chasial andonesympodial-dichasialbranchingandheterophylly(arrowpoints toscale-like prophylls).-
B& C: variation in shapeand sizeofprophylls; B:sympodialbranch unit arising inaxil ofone of
thepaired foliage leavesatthebottom,comprised ofstrongly anisophyllousprophylls, the foliage
leafpairatthetopandpairedthorns (bud:cf.D); C:scale-likeprophylls (arrow).- D:proximal part
ofasympodialbranch unitwith apairoffoliageleaves and pairedthorns;notebud inthe axil ofthe
left foliageleaf, from which anewsympodialbranch unit will develop.- E: ‘3-flowered’inflores-
cence,actuallycomprisedofa2-flowered anda 1-flowered inflorescenceon eithersideofpairedthorns
(t,cutoffthorn).- F:SEM-graphofthe baseofa2-floweredsympodialbranch unitshowing2 sets
ofpairedbracts and thebaseofthepedicels (p,p’)ofthetwoflowers;alsovisible:scarofaremoved
foliageleaf(*), stipule(arrow),pairedthorns (t, t’). - Scale bars: A: 10mm;B=C: 5mm; D =E,
F: 1mm. - Further explanationsin thetext.
314 BLUMEA VOL. 35,No. 2, 1991
thegenus. Theonly otherRubiaceaewithnodularroots known tous isPsychotria
ipecacuanha (Schumann, 1891:fig. 39F). Itis uncertainwhetherthe root structure
ofthesetwotaxa is comparable, however.
Neithertheroots ofMitchellarepens(seeHolm, 1907)nor those ofMitchellaun-
dulatashow any particularly unusualcharacteristics.
Fig.3. Seeminglyuniform,heterophyllousbranch ofDamnacanthus okinawensis(A) and ofD. bi-
florus(B). Inboth Aand B thebranchisactually comprised ofnumerous sympodial units,each
with apair ofvariously shapedsmall prophyllsand apair offoliage leaves;in theillustratedparts,
branching is strictly sympodial-monochasial.-Further explanationsin thetext.
E.Robbrecht,C.Puff&A.Igersheim: The genera Milchella and Damnac.anthus 315
4.1.3.Leaves and stipules
BothDamnacanthusand Mitchellahaveevergreencoriaceous leaves.Whilethe
leavesofMitchellaare uniform,theoccurrence ofheterophylly ischaracteristic for
Damnacanthus.Pairs ofrelatively large leaves (true foliage leaves) alternatewith
pairs ofsmall leaves(fig. 1C). Depending on the species ofDamnacanthus, the
smallleavesexhibita diversemorphology and canbe variablewithinan individual
(figs. 2A, 3 & 4). They maybe a) 'miniatures' ofthe large leaves but agreewith
theminshape, b)be differentin shape butstill foliage leaf-like, orc)be± scale-like.
Inthelattercase, they aremostly only comprised ofthestipular sheathsbearing ap-
pendage-like bladerudiments['Oberblatter']) on eitherside(fig. 4,insert).Thede-
greeofblade-'reduction'in the'small' leavesmay vary to someextent- even within
single individuals(figs. 2A-C, 3A). Smallleavesmay alsoexhibita certain degree
ofanisophylly (see fig. 2B).
InDamnacanthus, thisalternationbetweenlarge andsmallleavesis closely linked
withthebranching patternin thatthepairs ofsmallleaves invariably representpro-
phylls - seeparagraph 4.1.1forfurtherexplanations.
According toourobservations, prophylls are always present, buton branch sys-
tems where someor allofthemare very reduced,i.e. ± scale-like, theirpresence
maybeoverlooked unlessexaminedcarefully (cf. fig. 3).
Withinthe Rubiaceae,this kindofbranching pattern-linked heterophyllous leaf
arrangementappears tobe confinedtoDamnacanthus. Itis not comparable to the
threetypesofheterophylly recognized in thefamily by Robbrecht(1988: 49).
Domatiaare lacking onleavesofthegenusMitchella(as inall herbaceousangio-
sperms). They are probably alsoabsenton leavesofDamnacanthus(lacking in all
taxa examinedby us;relevantrecords inliteraturewere notfound).
Indumentum:Inthe species examined,leavesandothervegetativeparts are usual-
ly glabrous or puberulous. Theshortexternal hairsareofthecylindrical type(sensu
Robbrecht, 1988) andone-to few-celled, withnon-pitted outerwalls. - For internal
indumentumseeparagraph 4.3.
Leafanatomy: Anatomicalfindings published forMitchellarepens (Holm, 1907:
figs. 10-14) also apply toMitchellaundulata:theepidermis cells havemoderately
thickened outerwalls, andtheupperepidermis cells are larger thanthelowerones;
theleaves are hypostomatic; the mesophyll, with raphide-containing idioblasts, is
differentiatedintoone-totwo-layered palissades andaloosespongy mesophyll.
The leafanatomy oftheinvestigated taxa ofDamnacanthusis,in turn,similarto
thatofMitchella.Thereare minordifferencesbetweentheleavesoftheinvestigated
species DamnacanthusindicusandDamnacanthus macrophyllus. Themore coriace-
ous-leavedDamnacanthusindicushas anupperepidermis witha quitethickcuticle
and thecellsarerelatively small(but stilllarger thancellsofthelowerepidermis); as
compared toDamnacanthusmacrophyllus, theentire leafis somewhatthinnerbe-
cause ofthe more 'compact' mesophyll. Damnacanthusmacrophyllus has only a
single layer ofpalissade cellswhichare ± invertedly triangular inoutlineratherthan
± rectangular as in Damnacanthusindicus; the upper epidermis cells, also with a
massive cuticle, are markedly larger thanthelowerones.
316 BLUMEA VOL. 35,No. 2, 1991
Fig.4. Floweringbranch ofDamnacanthus macrophyllus(from colour transparencyPuffJP-1018)
comprisedofseveralsympodialbranch units. Note the alternation between pairs ofscale-like pro-
phylls(p) and pairs offoliageleaves, and therudimentarythorn (thinarrow) associated withafoli-
ageleafpair. Inflorescences areassociatedboth with foliageleaves (partly fallen off!) andprophylls
(thick arrow).Note also stigmasprotruding from flower-bud just about to open (open triangle).
Insert:Part ofasympodialbranch unit showing apairofprophylls (left)and the baseofafoliage
leafpair; notebifidstipules. - Theportion shown is c. 30 cm long;scale bar (insert):5mm. -
Furtherexplanationsin the text.
Nodeandpetioleanatomy:The two species of Mitchellaandtheinvestigated taxa
ofDamnacanthushaveunilacunarnodeswithone traceper gap.The arc-shaped leaf
trace givesoffasmalllateralbundleoneitherside shortly afterleaving thegap;these
lateralssupply thestipular sheath.InDamnacanthusitis noteworthy thatthevascular
cylinderofalateralbranch(i.e. new sympodial unit) startsforming before theleaf
trace gap closes again (fig. 5A). Theremay thus bea 'commongap' forleaftrace
and vascularsupply ofthelateralshoot.
Stipulesandcolleters:Thestipules of Mitchellaareentire; thoseofDamnacanthus
areeitherentireorbilobed,dependingonthespecies (seefig. 4,insert).
InbothMitchellaandDamnacanthusstipules are provided with± elongated coll-
etersofthestandardtype. ForMitchellarepensthey weredescribedas "long, slender
glandular hairs"byHolm(1907: fig. 14B),aninappropriate description as glandular
hairsinthestrict morphological-anatomical sense are absentin theRubiaceae(see
Robbrecht, 1988,fora discussion). Illustrationsofthemorphology ofthecolleters
ofMitchellaundulataare presented inNumata& Asano(1970: fig. Mitchellaundu-
lata, 12-13).- For colletersassociatedwith floralorgans seeparagraph 4.3.
4.2. Inflorescences
IndividualinflorescencesofMitchellaare typically 2-flowered, whereby theova-
ries ofthe two flowers are fused(fig. 6G; see paragraph 4.3 fordetails). Therecan
be somevariationin theinflorescencestructureofMitchellarepens(number offlow-
ers perinflorescence, arrangement,etc.; seeBlaser, 1954).Mitchellaundulatais es-