The status, ecology and relationships of Meziella (Haloragaceae)

7 Pages·1993·1.8 MB·English

by  A E Orchard

Nuytsia9(1): 111-117(1993) 111
The status, ecology and relationships of Meziella (Haloragaceae)
A.E. Orchard1 and G.J. Keighery2
‘AustralianBiologicalResourcesStudy,GPOBox636,Canberra,AustralianCapitalTerritory2601
-DepartmentofConservation&LandManagement,POBox51,Wanneroo,WesternAustralia6065
Abstract
Orchard,A.E.andKeighery,G.I.Thestatus,ecologyandrelationshipsofMeziella(Haloragaceae).
Nuytsia9(1): 111-117 (1993). The monotypicgenus Meziellahas until nowbeen known onlyfrom
its very fragmentary and immature type. Becauseofthisits statusasagenus andrelationshipshave
beenunclear,anditsdescriptionhasbeen incomplete. Recentrediscoveryofthespecieshasallowed
afulldescriptiontobepreparedforthefirsttime. ItisnowconfirmedthatMeziellaisadistinctgenus,
intermediate in many respects betweenHaloragis andMyriophyllum. Its somewhatbizarrefeatures
aredescribed,itsecologydiscussed,andarevisedkeytotheAustraliangeneraofthefamilyisprovided.
Introduction
Nees(1844)describedanewspecies,Gonocarpustrifidus,fromaPreisscollectionfromtheshores
ofalakenearAlbany inWesternAustralia. Theplantwasasmallcreepingherb,rootingatthenodes,
withtrifidleavesandyoungflowers. ThemaincollectionwasdepositedintheNeescollectionatLE,
but a small fragmentsubsequently found itsway toMEL.
Twoyearslater,Walpers(1846)transferredthespeciestoHaloragis,probablyfornobetterreason
than that itwasconsideredthatthetwo generawere synonymous. Thereis no indicationthathe re-
examinedthespecies,andeven ifhehad, itisunlikelythathecouldhavemademuch ofitwithonly
immatureflowersto work with.
TheonlycompleterevisionofthefamilyHaloragaceaetospecies level sinceWalper’streatment
isthatofSchindler(1905). Herecognisedtwosubfamilies, HalorrhagoideaeandGunneroideae, the
secondofwhichis nowgenerallyconsideredtoconstituteadistinctfamily,Gunneraceae. Schindler
dividedsubfamilyHalorrhagoideaeintotwotribes,HalorrhageaeandMyriophylleae,distinguishedby
thecharactersoftheendocarp. IntribeHalorrhageaethe1-4-locularovarydevelopsintoafruitinwhich
thewoodyorcrustaceousendocarpconstitutesasinglestructure,andthe1-4seedsineachfruitareshed
asaunitwithinthedrynut. IntribeMyriophylleae,containingonlythegenusMyriophyllum,thewoody
endocarp forms separately around each locule, and at maturity the fruit separates into two or four
1-seedednutlets.
Schindler re-examined the single collection of "Haloragis trifida", and decided, despite its
deficiencies, to segregate it as a distinct genus from Haloragis (which also included Gonocarpus).
112 NuytsiaVol.9.No. 1 (1993)
aprincipal distinguishingcharacterhe used thefactthat inMeziella (ashecalled it), thesepals were
much longerthan theovary, whereas in Haloragissensu latothey weremuch shorter. Healsodrew
attention to the tact that Meziella had only a single whorl of4 stamens, whereas most species of
Haloragis had a double whorl totalling 6 or 8 (the only exception known to him being Haloragis
(= Gonocarpus) nodulosa.
Inaseriesofpapers.Orchard(1975, 1976, 1977, 1979, 1980, 1981, 1986a, 1986b, 1990a, 1990b),
revisedthegenericandspecifictaxonomyoftheSouthAmerican,PacificandAustralian membersof
the family. In general Orchard adopted the generic circumscription ofSchindler, with two major
differences. Gonocarpus was re-instated as a genus distinct from Haloragis, and a new genus
Haloragodendronwascreated. Inbothcasesthecriticaldistinguishingcharactersweretobefoundin
thedevelopmentoftheovaryintothefruit.TheflowersofGonocarpus,HaloragisandHaloragodendron
all begin with fourovules in an ovary with essentially 4 locules (sometimesreducedto2or3ovules
andlocules). InGonocarpustheseptaareinsubstantialandincomplete,andarecrushedbythesingle
ovulewhichdevelopsintoaseed. Theovarywallbecomescrustaceousinfruit,buthardlywoody. In
Haloragisall4ovulescanpotentiallydevelopintoseeds,andtheseptaandendocarpbecomewoody,
formingasingle,indehiscent,dry,4-seedednutwhichisshedasasingleunit. Haloragodendronhas
afruit developmentsomewhat intermediate between Gonocarpus and Haloragis. In the flower the
ovary has substantial and complete septabetween the 4 locules (resembling Haloragis but only a
),
single seed isformed ineach fruit, crushing the septatooneside(as in Gonocarpus). However, the
endocarp becomes very woody, and the fruit increases in size considerably after anthesis (both
characteristicofHaloragis,butnotofGonocarpus). Othercharacterssupportthisgenericdisposition,
but thedevelopmental characters oftheovary/fruit werefound to be the mostdiagnostic.
OrchardconsideredthestatusofMeziellaintwopapers(1975, 1990b),butbecauseofthepaucity
andpoorqualityofthematerialavailablewasunabletodecideontheexactgenericstatusofthespecies,
andoptedtomaintainthestatusquountilmorematerialbecameavailable. Attentionwasdrawntothe
superficial similarityofthehabitandvegetativemorphologyofMeziellatosomebog-dwellingsmall
species ofMyriophyllum. Forexample, Myriophyllumlimnophilum hasavery closeresemblanceto
Meziella in habit and leaf shape, and is also found in boggy ground in the south-west ofWestern
Australia. However, withoutfruitsitwasimpossibletodecidewhetherMeziellawasinfactadistinct
genus,oronlyaspeciesofHaloragisorMyriophyllum. Inthelast 10yearsseveralsearcheshavebeen
madeinanattempttore-discoverMeziella,butintheabsenceofdetailsofitsoriginalcollection site,
all failed, and it wasfearedthatthe species(and genus) had becomeextinct.
Recently one ofus (GJ.K.) discovered a population ofa strange bog-dwelling plant at Chester
ForestBlock(34° ll'S, 115° 19'E),approximately30kmeastofAugusta,andabout200kmwestof
Preiss’originalcollectionfromnearAlbany,butstillintheWarrenBotanicalSubdistrict. Examination
hasconfirmed ittobe Meziella. The new discovery borecopious flowers and fruits, and thesehave
finally allowedthequestion ofthestatusofthegenustoberesolved. Inaddition, theecology ofthe
species can nowbe described.
ChesterBlockoccupiestheonlyremnantoftheNillupPlain remaining uncleared. This area isa
gently sloping pedimentofthe Blackwood Plateau, and is normally saturated orslightly submerged
duringwinterandspring. Meziellaoccursonslightlysubmergedflats,ongreysandyclaysoverclay.
It is found in very shallow (c. 5 cm deep) pools or prostrate on saturated soils in slightdepressions.
VegetationisalowheathofPericalymmacrassipesovermixedsedges(chieflyLeptocarpusandRestio
species). Scattered through thiscommunity areemergenttrees ofMelaleuca rhaphiophyllaand tall
shrubsofAdenanthosdetmoldii.
A.E.Orchard&G.J. Keighery,Meziella 113
Meziellacanover-summerinprotectedsitesasasmallrootstockwithshortdenseleafystemswith
linearleaves. However,manyplantsindriermoreexposedsitesdieduringthesummer. Regrowthand
germinationoccursasthewinterrainsfloodthesmalldepressionsandcontinuesuntiltheareabegins
to dry in Octoberand November.
Floweringcommences during November at Chester Block and continues until January. Mature
fruits are presentfrom January toFebruary. Floweringceases inJanuary andtheplants die orover-
summeras vegetative shoots until the next winter. Dispersal ofthefruithas notyetbeen observed.
ThestatusofMeziella
Meziellaisafairlybizarreplantatfirstsight,butperhapsnomoresothansomeofthemoreunusual
species ofMyriophyllum, such as M. callitrichoides, M. decussatum or M. coronation. In habit it
resembles several ofthesmall bog-dwellingsemi-aquaticspeciesofMyriophyllum. Theflowersare
bisexual, with the 4-merous plan common in Haloragaceae, but have disproportionately long and
narrowsepalsalmostequallingthepetals, unlikeanyotherspeciesinthefamily. Infruitthesesepals
becomestiffly erectorsemi-spreading,formingacoronaofsoftspinesatthesummitofthefruit. At
thesametimefurthersoftspine-likeprocessesaredevelopedinthelowerhalfofthefruit,withgroups
of6-7 "spines" beloweachsepal. Theselowerspinesarepresentintheflower,butareveryreduced,
and expand rapidly once thepetals and stamens are shed. They were not observed by any previous
author.
ThestamensofMeziellaarealsosomewhatunusual. Onlyasinglewhorlof4ispresent,unlike-the
doublewhorlnormalinthefamily. Thisreductioninnumberoccursoccasionallyinothergenera,e.g.
in Gonocarpus nodulosus, Myriophyllum integrifolium, M. limnophilum, M. callitrichoides subsp.
callitrichoides and M. mattogrossense, but is not common. In addition, the anthers in Meziella are
distinctlyapiculate. Thisisanunusualfeatureinthefamily,foundinmostspeciesofGlischrocaryon,
all species of Haloragodendron, and rarely in Myriophyllum (e.g. M. coronatum, M. muricatum,
M. mattogrossense).
AsinmanyotherHaloragaceae, whiletheflowersofMeziellaaremorphologicallybisexual,they
areoftenfunctionallyunisexual. Intheinflorescencethereisagradationfromflowersatthetopofthe
spike which are functionally maleby virtueoftheirprotandry, and which through truncation ofthe
growingseasonwillprobablyneverdeveloptheirfemaleparts,tothoseinthecentralregionofthespike
which, having shed their pollen develop their stigmas, become pollinated themselves and develop
rapidly tofruit,andthosetowardsthebaseofthespikein whichtheanthers,althoughpresent,donot
splitopentoreleasepollenandarethusfunctionallyfemale. Asimilargradationisnotunusualinmany
species ofMyriophyllum and insomespeciesofHaloragisand Gonocarpus.
,
Theovary/fruitdevelopmentprovidesthefinalevidencethatMezielladeservesitsseparategeneric
status. Theovaryis4-locularwithwell-definedsepta,andasinglependulousovuleineachlocule(i.e.
identicalwithHaloragisandHaloragodendron). Eachoftheseovulesdevelops,potentially,toform
aseed. Intheprocesstheendocarparoundeachloculebecomeswoody,butunlikeHaloragis, where
asingle4-locularwoodymassisformed,inMeziella4separatewoody I-seededpyrenesdevelop. This
issimilartothesituationinMyriophyllum,buttheretheexocarpsplitstoallowthemericarpstoseparate
fordispersal. ThisdoesnothappeninMeziella. Herethefruitremainsindehiscent,andthefourpyrenes
ormericarps areshedasaunit, bound togetherby thespinyexocarp.
114 NuytsiaVol.9,No. 1 (1993)
The above combination ofcharacters is sufficient to confirm the status ofMeziella as adistinct
genus. Its relationships seem to be with Myriophyllum, with which it shares its sub-aquatic habit,
dissectedleaves,andfruitsinwhichtheendocarpbecomeswoodyaroundeachindividualloculerather
thanaroundthefruitasawhole. HoweveritdiffersfromMyriophylluminthatthefruitdoesnotseparate
intomericarpsatmaturity. Thesubulatesepals,equallingthepetalsinlength,andpersistingasspines
on thefruit, servetosetthe taxon apart from all others in the family.
Schindler’shigherlevelclassificationneedsmodificationwiththediscoveryofthedevelopmental
structure of the fruit in Meziella. His tribe Myriophylleae was established on the basis that
Myriophyllum differed from all othergenerain having afruitwhich splitintomericarps atmaturity,
whereasthefruitsofthegeneracomprisingtribeHalorrhageaewerecompletelyindehiscent. Meziella
straddlesthisdivide. HoweveritcanbeaccommodatediftribeMyriophylleaeisredefinedashaving
1.
afruitmadeupof1-seededpyrenes,whiletribeHalorrhageaehasafruitinwhichallcarpelsarefused
in2t.oasingleunit,whichmaycontainasfewas 1 seed,orasmanyas4,butisneverdividedintopyrenes.
Thi3s.modifiedclassification isreflected in thekey togenerabelow.
4.
Key to thegeneraofHaloragaceae
Fruitan indehiscent 1-4-seeded nutnot subdivided into 1-seeded
pyrenes TribeHalorrhageae
Allflowers with petals
Petals hooded; anthers non-apiculate; inflorescence indeterminate
Fruits (2-3)4-locular, pericarpwoody with solid septa; flowers in
6.
(l)3-7-flowered dichasia in theaxils ofalternatebracts Haloragis
4. Fruits 1-Iocular, pericarpcrustaceous with nosepta(crushed by
7. single seed); flowers solitary (veryrarely 1-3) in the axils ofopposite
oralternatebracts Gonocarpus
3. Petalsnavicular; anthers usually apiculate; inflorescencedeterminate
5. Leavesserrate; inflorescence narrow, spike-like; shrubs orsmall
trees with 1-few woody stems/trunks Haloragodendron
5. Leavesentire; inflorescence broad,pseudo-umbelliform; subshrubs
with numerous annual stemsarising from aperennialrootstock Glischrocaryon
2. Atleastfemale flowers lackingpetals (rudimentary petals in Proserpinaca)
6. Fruit 1-locular; flowerspredominantly unisexual, in dichasiaofupto
about 11 flowersperaxil, the terminal one ineachdichasium usually
male, theothers female orrarely bisexual; anthers linear-oblong Laurembergia
Fruit 3-locular; flowers bisexual, solitary orindichasiaofupto3
flowers peraxil; anthersellipsoid Proserpinaca
1. Fruit madeup of 1-seeded pyrenes TribeMyriophylleae
Fruitsplitting at maturity intomericarps; sepals less than halflength
ofpetals (frequently absent), flat, lanceolatetoovate; flowers
frequently unisexual Myriophyllum
7. Fruitnotsplitting atmaturity intomericarps; sepals almostequalling
petals in length, subulate, developing into softspines; flowersbisexual Meziella
A.E.Orchard&G.J. Keighery.Meziella 115
Figure1. Mez.iellalrifida. A-habit. B-trifidleaffromthemid-stemregion.C-flowersubtendedbytwobracteoles. D- petal.
E-stamen. F-bracteole.G-tipofinflorescenceshowingbuds,andflowersatanthesis. H-oldflower/youngfruit. I-mature
fruit. J-transversesectionoffruitshowingthefourpyreneswithinasinglepericarp. Scalesrepresent1cm(A)or1 mm(B-J).
AllillustrationsarefromKeighery 12789.
116 NuytsiaVol.9,No. 1 (1993)
Description ofMeziellatrifida
Meziella trifida (Nees) Schindler, Pflanzenr. 23: 61 (1905) (Figure 1)
Gonocarpus ['Goniocarpus'] trifidusNees in Lehm., PI. Preiss. 1: 159 (1844)
Typus:"InturfosishumidisadlacumhaudproculaboppiduloAlbany (Plantagenet)m.Octobri 1840.
Herb. Preiss. No. 2401". Holo: LE; iso: MEL
Haloragistrifida (Nees)Walp., Rep. 5: 672 (1846)
Illustrations: Schindler, Pflanzenr. 23: 61, fig. 18 (1905); Blackall &Grieve,W. Austral.Wildfls 3:
463, 472 (1965); Orchard, FI. Austral. 18: 86, fig. 29A-F.
Decumbent, glabrous, annual or perennial semi-aquatic herb, reddish in mostparts; main stems
prostrate,rootingatthenodes,freelybranched;lateralstemsascending,apparentlyallbecomingfertile.
mm mm
Leavesalternate,subfleshy,thelowermostoneachstementire,linear,3.5-5.0 long,0.4 wide,
sessile,tipacute;middleandupperleavesoneachstembecomingtrifidwith2linearlobesatorabove
the middle and ± equalling central lobe in length; each lobe tipped with a hydathode, and tiny
hydathodessometimes alsopresentin the axilsofthelobes. Inflorescencean indeterminatespikeof
flowersbornesingly intheaxilsofslightlyreducedupperleaves(bracts)oneachlateralstem. Bracts
trifidinthelowerpart,becomingentireabove,leaflike. Eachflowersubtendedbyapairoflanceolate
mm mm
or narrowly deltoid bracteoles, which are red, acute, entire, 1.0 long, 0.3 wide. Flowers
mm mm
4-merous, bisexual, sessile. Sepals4, red, subulate, 1.7 long,0.3-0.35 wide,entire,smooth,
mm mm
erect. Petals4,red,narrowlyhooded, 1.7-1.8 long,0.2 wide(keeltomargin),withadistinct
apiculum; shed almost immediately after anthesis. Stamens 4, antisepalous;filaments deep red,
lengtheningto0.4-0.5 mm; anthersyellowtoreddish, narrowlyoblong, 1.2mm long,0.25mmwide,
distinctly apiculate, sometimes indehiscent in lower flowers. Styles 4, reddish, clavate; stigma
mm
papillate. Ovarysmall,c.0.5 diameter,±globular,withclustersofshortsubulateprocessesbelow
thesepals;4-locular;expandingrapidly infruit. Fruitred, indehiscent,of4woody 1-seededpyrenes
containedwithinadryexocarp. Sepalspersistent, increasing insizeandthicknesstoformaterminal
mm
corona; clusters of6-7 soft spreading spines to 1.3 long develop on the lower halfofthe torus
mm mm
beneath each sepal, upper halfoftorus smooth. Fruit (including spines) c. 2.7 long, 2.7 in
diameter.
Specimens ofthe new collection (G. Keighery 12789) have been lodged atPERTH and HO.
References
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Glischrocaryon. MeziellaandGonocarpus. Bull.AucklandInst.Mus. 10: 1-299.
Orchard,A.E. (1976). RediscoveryofGonocarpustrichostachyus(Haloragaceae). Rec.Auckland Inst. Mus. 13: 109-110.
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