Fossil Polypodiaceae and their spores

20 Pages·1991·1.4 MB·English

by  Van Uffelen, Gerda A

BLUMEA 36 (1991) 253-272
Fossil Polypodiaceaeand theirspores
Gerda+A. van Uffelen
Rijksherbarium /HortusBotanicus, Leiden,The Netherlands
Summary
In thispublicationemphasisis laidonthemodern definition ofthe familyPolypodiaceae(Fili-
cales),which is based onan extensivestudy ofRecentmaterial and which is muchrestricted with
respect to older circumscriptions ofthe family asusuallyappliedby palaeobotanists. Fossils of
femsbelongingtothefamily in the strictsenseareextremelyrare and thoseexamined donotbear
anyspores suitable forstudy.Ofthe fossils attributed tothe family in itstraditional,large sense,
only asmall minoritybelongstothefamily in itsstrictsense.
Asurvey ofthefew polypodiaceousfossilsknown totheauthor is giventogetherwith alistof
non-polypodiaceousfossils that usually(sometimestentatively) have been referred to the family
Polypodiaceae.
Introduction
Inpalaeobotanical literature,asintheolderactuobotanicalliterature(Diels, 1902;
Christensen, 1938),thefamilyPolypodiaceae is usually definedinawidesense. In
many publications (Arnold, 1964;Taylor, 1981; Meyen, 1987) itcomprises a large
partoftheleptosporangiate fems.Thisextremelywide conceptofthefamily hasno
place inanaturalclassification, as itis probably not monophyletic: somegroups in
the family s.l. maybemoreclosely relatedto groupsoutsidethatfamily thantothe
othergroupswithinit(see,e.g.,Holttum, 1949;Lovis, 1977).
In the polypodiaceous part of leptosporangiate fems ever more supposedly
monophyletic familieshavebeenrecognized during thepast fiftyyears (e.g.,Crabbe
etal., 1975;Kramer& Green,1990).OneoftheseisthefamilyPolypodiaceae inits
restricted sense.
Onereason forthesometimesspectacular changes intaxonomicviewsisthatfora
long time ithasbeendifficultto assess whichcharacters infemsbestreflectnatural
relationships. Inthe course ofthis century theimportance ofsoralcharacters has
beenreduced dramatically totheadvantage ofe.g.charactersofthefrond indument.
Fromthepoint ofviewofthepalaeobotanist the way Recentfernclassification
keeps changing is very annoying. Ifactuopteridologists with theirabundantdata
cannot cometo a stable classification, why then should palaeobotanists botherto
keep upwithmodemfemclassification?Apartfromthis, thedetailedclassifications
basedonRecentmaterialoftenare notdirecdy applicable inpalaeobotanic research:
palaeobotanists usually haveabroadconceptoftaxonomicgroups,possibly due to
254 BLUMEA VOL.36, No. 1, 1991
thelargenumberofextincttaxa andtotheusually smallnumberoffossilsavailable
tocircumscribeataxon. Inthe case ofthePotypodiaceae therelatively smallnumber
offossilizedleptosporangiate fernsavailablemustplay arole.
However, bothpalaeo- andactuopteridologists have important contributionsto
make totheelucidationofrelationships inferns,and so toastable, naturalclassifi-
cation.
TotheRecentpteridologist, adetailedpictureofrelationships onwhichaclassifi-
cationcanbebasalisnecessary inordertorevise generaorgroupsofgenera.There-
fore,thestrictdefinitionofPotypodiaceae is animportantsteptowardsanew, stable
classification.
Inthispublication a definitionofPotypodiaceae inthestrict sense willbe given,
emphasizing thosecharactersthatappeared tobeusefulin assessing thetaxonomic
position ofRecent ferns. A morestrict definitionofthisfamilyandofthefamilies
formerly thought tobelong tothePolypodiaceae, willnot renderthe palaeobotanist's
work more cumbersome- indeed, itmayofferheror him somenew charactersfor
study andanindicationofthe taxonomicimportanceofthecharactersused,basedon
anextensive study ofRecentmaterial.
Theapproach adopted here,thatis, tolookforFossil representatives ofasmall,
well-circumscribedgroupofRecentorganisms, is unusual in palaeobotany. Ithas
not led totheresults hoped forattheoutset. However,ithasshownup somepecu-
liarconsequences(from thepointofviewoftheactuobotanist)ofthe usualpalaeo-
botanical approach, viz., study eitherallfossils froma certainageandplace (includ-
ing representatives oftaxonomically 'difficult' groups),orall Fossilrepresentatives
ofa(form-)taxonofwhichsufficientmaterialisavailable.
THEFAMILY POLYPODIACEAE S.S.
Introduction
Fernsare usually treatedas one divisionoftheplantkingdom: the Filicophyta
(e.g., Andrews & Boureau, 1971) orPteridophyta (e.g., Meyen, 1987).However,
opinions onrank andnames within this division may vary considerably between
authors.Thetrue fems, thatisexcluding theso-calledfern-allies(Psilotopsida, Lyco-
podiopsida, Equisetopsida), are usually all placed intheclassPolypodiopsida (syn-
onyms: Pteropsida, Filicopsida) and contain the following groups with Recent
representatives: Ophioglossales, Marattiales,Osmundales,Filicales, Marsileales,and
Salviniales.
In thepalaeobotanical literaturetheorderFilicalesincludesusually6-9families
withRecentrepresentatives (Andrews &Boureau, 1970;Taylor, 1981; Meyen, 1987).
Schizaeaceae, Gleicheniaceae,Cyatheaceae, Dicksoniaceae, Matoniaceae,Davallia-
ceae, Hymenophyllaceae, Dipteridaceae, andPolypodiaceae are thefamiliesgenerally
distinguished. ThenamePolypodiaceae is usually applied initsold-fashioned,broad
sense.
In thefirst halfofthis century, mostactuopteridologists referred tothe classi-
ficationpublished by Diels (1902). So didBower (1923), a pteridologist whose
morphological analysis ofa great manyfems hasformeda basis formanyofthe
G.A.vanUffelen: FossilPolypodiaceae and their spores 255
earlierattempts atfem classification.Inapplying Diels'broadconceptofthefamily
Polypodiaceae (containing 114generaand 4527 species), he described its main
charactersas follows:annulusvertical; son marginal or superficial, andmixed(that
is, thesporangia donot mature in a set order). His viewcorresponds with that of
mostpalaeobotanists, whouse theverticalannulusas themaincharactertorecognize
a'polypodiaceous' fem.
Inthecourse ofthiscentury, thepolyphyletic originofthePolypodiaceae s.l.has
beenindicatedby manypteridologists (e.g.,Copeland, 1947;Holttum, 1949;Lovis,
1977). Thishas resultedin a significant reduction in size ofthisfamily because
several large, supposedly monophyletic familieshave been recognized in it, viz.,
Adiantaceae,Dennstaedtiaceae,Thelypteridaceae, Aspleniaceae, Davalliaceae, and
Blechnaceae.Thefollowing groupsare nowalsoexcluded fromthePolypodiaceae
s.s.: Cheiropleuriaceae, Dipteridaceae, Grammitidaceae(Hennipman etal., 1990;
Jarrett, 1980),and, by some authors (Pichi Sermolli, 1974; Hennipman & Roos,
1983),Loxogrammaceae.
Lovis(1977), whohas published on bothRecentandFossil fems, uses theterm
'polypodiaceous', in quotes,for all 'truly leptosporangiate ferns', thatis, all ferns
Bower(1928) called'inanolderterminology thePolypodiaceae.' They are charac-
terizedby 'the smallleptosporangiate sporangium, containing only 64 spores, and
theverticalannulus.' He describedthreemainradiations withinthis group,between
whichtherelationsareunclear:the dennstaedtiaceousradiationoffernswithindusi-
atesuperficial son (Dennstaedtiaceae,Davalliaceae,Blechnaceae,Aspleniaceae,Dry-
opteridaceae, Thelypteridaceae, Lomariopsidaceae), theadiantaceousradiation,with
marginal or submarginal son (AdiantaceaeandParkeriaceae)andthepolypodiace-
ous radiation,characterizedby nakedsuperficial sori (Polypodiaceae, Dipteridaceae,
Cheiropleuriaceae, Grammitidaceae). Heapplied thenamePolypodiaceae in are-
stricted sense.
Recent research
Foraboutten years,thestudy ofthefamilyPolypodiaceae s.s.hasbeenstimulated
andcoordinatedfromUtrecht, theNetherlands,by Hennipman (1984,1985).Several
studieshavecontributedtothe knowledge aboutthisfamily by way ofmonographs
(Platycerium: Hennipman & Roos, 1982;Drynarioideae: Roos, 1986;Pyrrosia:
Hovenkamp, 1986;Lecanopteris p.p.: Hennipman & Verduyn, 1987;Goniophle-
bium:Rodl-Linder, 1990;Polypodium loriceum-complex: Hensen, 1990;Micro-
sorum: Bosman, 1991)andanalyses ofcertaincharacters (stomata: Sen& Hennip-
man, 1981;venationpatterns:Hetterscheid&Hennipman, 1984;paraphyses: Baayen
& Hennipman, 1987a,b; spores: VanUffelen& Hennipman, 1985;Hennipman,
1990;sporogenesis: VanUffelen, 1990).
Circumscription of the Polypodiaceae s.s.
Themostrecent and detailedcircumscription ofthePolypodiaceae s.s. is given
by Hennipman et al. (1990). They include29 genera,two ofwhich may also be
placed intheseparatefamilyLoxogrammaceae (Pichi Sermolli, 1974;Hennipman &
256 BLUMEA VOL. 36,No. 1, 1991
Roos, 1983),andabout660species inthefamily, whichis asubstantialreductionin
size compared to Bower'streatment - evenmore so ifoneconsidersthelarge num-
berofnewfernspecies describedsince Bower'stime.
ThePolypodiaceae s.s. (Loxogrammaceae excluded) arerelatively small, often
epiphytic femswith acreeping dorsiventralrhizome bearing scales (nohairs)and
witha dictyostele.
Thefrondsarearticulatetophyllopodia anddeciduous,rarelypersistent; they are
usually simple, pinnatifid, or simply pinnate, rarelybipinnatifid, neverregularly bi-
pinnate or more divided; pedately, hastately, or dichotomously dividedfronds are
foundinsomegenera.Frond dimorphy occurs insomegenera:frondsmaybe differ-
entiatedintonormalfrondsandnest frondsfortrapping litter; fertilefrondsmaydiffer
dramatically fromsterileones,butmanyspecies havefrondsofonlyonetype.Vena-
tionis characteristically anastomosing, theareolaeusually bearing oneor morefree
veinlets, butinsomegeneraopenvenationoccurs (forvenationseeHetterscheid&
Hennipman, 1984;Mitsuta, 1981:figs. 1-270,1982:figs. 1-113,1983:figs. 1-355,
1984a:figs. 356-608, 1984b:figs. 750-904).
Sporangiaare groupedinexindusiatesori onthelowersurfaceofthelamina.Sori
are usuallyround, butmay beaggregated intolinearcoenosori(butneverelongated
along theveinsas inAsplenium) or even cover thegreaterpartofthelowerlamina
surfaceincase offertilepinnaewithastronglynarrowedlamina.
Sporangia usually havea3-seriated stalkandacapsule with averticalandinter-
rupted annulus; they contain64spores,rarely 8 or 16.
Spores aremonolete,thewallconsistingof asmoothtoverrucate orrugulate exo-
sporeofthe blechnoidtype, coveredby aperispore thatvariesfromvery thinand
closely adhering totheexospore,tovery thickandcomplex.
NON—POLYPODIACEOUS FOSSILS
Underthis heading those macrofossils are mentionedthatinthe standardworks
by Andrews & Boureau (1970), Taylor (1981), and by some others, have been
placed inthefamilyPolypodiaceae s.l. Theydonot belong to thefamilyPolypodi-
aceae s.s. ForRecent ferns, Kramer& Green(1990, includingHennipman etal.on
Polypodiaceae), is used as theworkofreference.Foreach genus,anotherfamily
assignment is indicatedwhereverpossible.
1.Acrostichum L. (Pteridaceae-Pteridoideae)
TheRecent genusAcrostichumisrelatedtothegenus Pteris.Fossilfindsinclude
Acrostichumanglicum Collinson,basedon dispersed sporangialmasses andindivi-
dualsporangia with triletesporesfromtheBritishTertiary. Variousplantparts(see
Andrews & Boureau, 1970; Taylor, 1981), suchas rhizomes bearing petioles and
sterileandfertilepinnae withsporangia containing trilete, smoothspores,havebeen
describedas Acrostichum ?aureumL.by Wilde(Middle Eocene,Messel)or as Acro-
stichumpreaureumby ArnoldandDaugherty (Eocene,Clamochertbeds). Theyare
supposed tobeconspecific with theRecentspecies Acrostichumaureumby Barthel
(1976) andWilde(1989).
G.A.vanUffelen: FossilPolypodiaceae and their spores 257
2. AdiantitesGoppert (incertae sedis)
According toLovis(1977) 'recordsofAdiantitesneedtobeevaluatedwithpartic-
ularcircumspection, sincethisis aform-genus towhichareattributedCarbonifer-
ous andPermianfossils whichare not evenferns atall, butpteridosperms.' Fossils
placedin thisgenus are,e.g.,Adiantiteslatifolius Andrednszky (Miocene ofKerec-
send,Hungary; aleafliketheRecentAdiantumreniforme L.), Adiantiteslindsayoi-
desSewardfromthe Jurassic, andAdiantitesoblongifolius GoppertfromtheLower
Carboniferous(seeAndrews &Boureau, 1970).Inthe descriptions thefrondparts
are saidtobelikethoseofAdiantum(Pteridaceae-Adiantoideae)orLindsaya (=Lind-
saea,Dennstaedtiaceae-Lindsaeoideae).
3.AdiantumL. (Pteridaceae-Adiantoideae)
Fossils describedinthe genus AdiantumareA. anastomosum Brown (Eocene),
ofwhichthegeneric nameis doubtfulasthespecies is basedon poormaterial(An-
drews& Boureau, 1970),andAdiantumfrancisi Ball (Eocene),ofwhichAndrews
& Boureau(1970) statethatitisbasedon onlyonepinna.
4. Allantodiopsis erosa Knowlton et Maxon (incertae sedis)
Thisfossil fromthePaleoceneofColorado(see Andrews &Boureau, 1970) is
definitely non-polypodiaceous because ofits son, which are elongated along the
veins.
5. Aspidistes Harris
Aspidistes thomasi (Thelypteridaceae?)
Aspidistes beckeriandA.sewardi (Matoniaceae?)
Threefossilspecies havebeendescribed in thegenus Aspidistes. Thetype spe-
cies is A. thomasi(Harris, 1961)fromthe Yorkshire Jurassic. Harris mentionsno
definite,obviousrelationship but 'Aspideae?', anamenot concurrent withnomen-
claturalpractice (Greuter etal., 1988). Andrews& Boureau(1970) assign it tothe
familyPolypodiaceae s.l. and state that 'il seraitleplus ancien fossiledePoly-
podiaceae connu.' As to its affinities, Lovis (1975) statesthat 'though noliving
thelypteroid possesses allthecharacteristicsofAspidistes thomasi,thereis no char-
acterofthisfossilwhich cannotbematchedsomewhereamongstmodemTheiypteri-
daceae.'
OfAspidistes beckeri(Lorch, 1967) fromthe Jurassic, thevenationandarrange-
mentofthesori havebeenpreserved, butnot thesporangia and spores.Lovis(1977)
writes 'Itis unfortunatethatthisfossilshouldhavebeenplaced inthesame genusas
A. thomasi, sincethese two species arealmostcertainly unrelated.Thetrue affinity
ofA.beckeri is problematical, butitis surely not thelypteridaceous, anditneednot
necessarily bea 'polypodiaceous' fem.On the contrary,thecuriousvenationsug-
geststomethepossibility thatitmaybeamemberoftheMatoniaceae... Aspidistes
sewardi fromLowerCretaceous rocks inEngland (Watson, 1969)is apinna frag-
ment,resembling A. beckeri, but 'just as distinctfromA. thomasi’(Lovis, 1977).
He states thatbothfossils areprobably matoniaceousferns.
258 BLUMEA VOL. 36,No. 1, 1991
6. Asplenium L. (Aspleniaceae)
Many different,probably not very closely relatedfossils, datingfromtheLower
Cretaceousonward,havebeenplaced inthegenusAsplenium (Lovis, 1977).Forin-
stance, Asplenium alaskanumHollick (Tertiary, seeAndrews &Boureau, 1970) is
not an Asplenium, butis morelikely tobeaDiplazium (Dryopteridaceae-Athyrioi-
deae)(Hovenkamp, pers. comm.).
7. Astralopteris Tidwell, Rushforth& Reveal (incertae sedis)
TheCretaceousfossil femAstralopteris coloradicawasfirst describedby Brown
intheRecentgenusBolbitis(Lomariopsidaceae) (seeHennipman, 1977). Thespecies
was basedonsterilematerialonly, andas soonasthey hadstudied fertilematerialof
thespecies,Tidwell, Rushforth& Reveal (1967)placed itinthenewly-erected genus
Astralopteris.They mentionthatLellinger, anactuopteridologist, foundittoresemble
mostclosely species oftheRecent genusDrynaria, amemberofthePolypodiaceae
s.s. Lovis (1977)statesthatitresemblesinparticular Drynaria rigidula (Schwartz)
Bedd. in pinna shape andsoraldistribution.Hovenkamp (pers. comm.), an actuo-
pteridologist, states thatthisfossil doesnot belong to thePolypodiaceae, as thein-
nervationofthesori looksatypical foranyPolypodiaceae (seeRoos, 1986:pl.30-34,
37, 38, 40).
8.DennstaedtiaBernhardi(Dennstaedtiaceae-Dennstaedtioideae)
Of theRecent genusDennstaedtia, two species are mentionedby Andrews &
Boureau(1970): D.americanaKnowlton(Paleocene)andD.tschuktschorumKrysh-
tofovich(Cretaceous).
9. Dennstaedtiopsis Arnold et Daugherty (incertae sedis)
Dennstaedtiopsis aerenchymata Arnold&Daugherty (Eocene) isdescribedas poly-
podiaceous by Taylor (1981): 'horizontally orientedrhizomesthatbearalternately
arranged, distinctlyspaced pinnae ... thedistalportions ofthefrondare notknown
...'; Andrews& Boureau(1970) concludethatitisanaquatic fem,thefossil consist-
ing ofmineralizedrhizomesandpetiolebases; they place itinthesubfamilyDenn-
staedtioideae(Dennstaedtiaceae).Itis definitely non-polypodiaceous, asPolypodia-
ceaes.s.havea highly dissectedstele(dictyostele).
10.Dryopteris Adans. (Dryopteridaceae-Dryopteridoideae)
Dryopteris meeteetseana Brown(Paleocene); citedby Andrews& Boureau(1970)
asbeing thebest conservedpolypodiaceous fossil,although thesporeshavenotbeen
preserved.
11.Leptochilites Andreánszky (incertae sedis)
Leptochilites sarmaticushasbeendescribedbyAndre&nszky (1959, Miocene). He
states thatitis asterilefempinna, whichhasnot beencompletely conserved. There-
G.A.vanUffelen: FossilPolypodiaceae and their spores 259
foreheconcludes'eineEinreihung ineineechte Gattung nichtrichtig undzogenwir
vor,einekunstliche Gattungaufzustellen.' Although the depicted pinnamaybepoly-
podiaceous, dataon thesoral disposition are neededto verifythis.
12. OnocleaL. (Dryopteridaceae-Athyrioideae)
Onoclea hesperia Brown (Paleocene) is citedby Taylor (1981)as being poly-
podiaceous. Andrews & Boureau(1970) finditto beratherliketheRecentspecies
O. sensibilisand concludethatitshouldbeincludedinthatspecies. Materialplaced
by Andreanszky (1959, Miocene) in Onoclea sensibilisconsistsofjustonebadly
conserved pinna. The materialofO. inquirenda Hollick (Cretaceous) is cited by
Andrews andBoureau as being ofpoorquality. Onoclea sensibilisL. var.fossilis
Newberry (Oligocene?) isalsobasedonpoormaterial.
13. Polypodites Göppert (incertae sedis)
TheFossil genusPolypodites hasbeenbasedby Goppert (1836) on a non-poly-
podiaceous fossilhenamedPolypodites mantelli.Itis not clearwhy heremovedthe
speciesLonchopteris mantellitothisnew genus.Goppertplaced 7species inhisnew
genus, someofthemdatingfromtheCarboniferous.As healsoplaced severalbipin-
natifidspecies in thegenus(e.g.,Polypodites elegans), notallthespecies assigned
to thegenus fallwithin thePolypodiaceae s.s. Muchofthematerial(e.g., thatof
P. lindleyi) is very fragmentary.
Subsequently, manyspecies havebeenplaced inthegenus(seeJongmans &Dijk-
stra, 1963;Dijkstra& VanAmerom, 1985;Andrews&Boureau, 1970).Lateraddi-
tions includePolypodites polysorusPrynada andP. verestchaginii Krassilov, both
depicted inKrassilov (1967). Polypodites polysorus probably belongs inthefamily
Cyatheaceae becauseofthebranchingpattern,the'knobbly' sori,andthetriletespores
(Hovenkamp, pers. comm.), whilePolypodites verestchaginii, whichis sterile, may
belong tothefamiliesPteridaceaeorThelypteridaceae.
14.Polypodium L. (Polypodiaceae-Polypodioideae)
Lovis (1977) describedPolypodium oregonenseFontaineas 'utterly unlike...any
known genusofPolypodiaceae (s.s.) and ... more consistent with Cyatheaceae,
though withoutproperstudy thissuggestion has scarcely moremeritthanFontaine's
determination.'
Other species described in the genusPolypodium (see Fossilium Catalogus =
Jongmans &Dijkstra, 1963;Dijkstra& VanAmerom, 1985) willbetreatedinasub-
sequentpublication onFossil species ofPolypodium.
15. PteridiumScopoli (Dennstaedtiaceae-Dennstaedtioideae)
Pteridiumcalabazensis(Dorf)Graham(Miocene,Pliocene) isregarded as thefos-
silequivalent ofthe Presentspecies Pteridiumaquilinum (L.) Kuhn, whichisalso
foundas an abundantPleistocenefossil (Andrews & Boureau, 1970). Itis notre-
gardedas apolypodiaceous fern.
260 BLUMEA VOL. 36,No. 1, 1991
16.PterisL. (Pteridaceae-Pteridoideae)
Pterispalaeoaurita Kov£cs (Miocene)isbasedonsterilematerial, sothatitsplace
inthe genusis uncertainandprovisional (Andrednszky, 1959).
17.Salpichlaena Hooker (Blechnaceae-Blechnoideae)
TheFossil species Salpichlaena anceps(Lesquereux) Knowlton(Paleocene)israth-
er liketheRecentspecies Salpichlaena volubilisaccording toAndrews& Boureau
(1970).
18. WoodwardiaJ.E. Smith (Blechnaceae-Blechnoideae)
TheRecentgenusWoodwardia,liketheRecentgenusOnoclea,usedtobeplacedin
thePolypodiaceae. Andrews& Boureau(1970) notea closeresemblancebetween
sterilefrondsofthetwo genera,whichare now placed intwo differentfamilies
(Blechnaceae andDryopteridaceae, respectively). AndrewsandBoureaumentionthe
Fossil species Woodwardiaarctica (Heer) Brown (Paleocene), whichincludes W.
maxoniKnowlton,basedonfertilefrondparts,andW. columbianaKnowlton(Pleis-
tocene?).
POLYPODIACEOUS FOSSILS
1. Aglaomorpha heraclea (Kunze) Copel.
Inthebeginning ofthis century, Toblerfounda 5 cm long fertilepartof afossil
fernfrondinPalembang Province, Sumatra, datedasTertiary,possibly Upper Mio-
cene in age. Krausel (1932) showed itto Christ, and they identifiedit as abasal
pinna ofafertilefrondofPolypodium quercifolium L. [=Drynaria quercifolia (L.)
J.Smith], basing theiridentificationontheplace of thesori, the venationpattern,
and the thickness ofthe veins.Roos, in his monograph ofthe drynarioid ferns
(1986), assigned ittoAglaomorpha heraclea(Kunze) Copel. The NaturalHistory
Museum in Baselkindly lentme thespecimen. Although Krausel states thatsome
spores werepresent atthetimehe studiedthefossil ('Vereinzelt sindauchSporen
vorhanden,einzeln oderin Paketenbis zu vierenvereinigt...'), I didnot findany
spores suitableforfurtherstudy.
2. Polypodium L. species
In 1937,MacGinitiedescribedafossilfoundin Redding Creek, Californiaunder
thenameofPolypodium fertile: 'Thisfossilinallits charactersis nearly identical
withtheliving Polypodium vulgare var. occidentaleHook.' Itcertainly lookslikea
Polypodium, but, despite theepithet, nosporangia orspores haveasyetbeenfound
preserved on the specimens. Further study has shown theWeaverville flora to be
MioceneratherthanEoceneinage(Doyle, pers.comm.).
Afossilfoundin theFortunaMinenearBergheim inGermany during anexcur-
sionin whichpalaeobotanists fromUtrechttookpart, hasbeenbrought tomy atten-
tionby Vanden Burgh. Itcomes from theRottonschichtenFormation, and dates
G.A.vanUffelen: FossilPolypodiaceae and their spores 261
fromtheBrunssumien(Pliocene). Itcanbeassigned tothePolypodiaceae s.s.andis
probably aspecies ofPolypodium. Itwillbefurtherdescribedandpublished by Van
UffelenandVanderBurgh. Somesporeswerefoundandstudiedwiththescanning
electronmicroscope. They are clearly monolete,buttoo youngto concludeanything
aboutthesurfacepatternof thematurespore. Thefossilis deposited inUtrechtunder
thenumber11409.
Inthe samepublication, severalFossilspecies ofPolypodium as listedin theFos-
siliumCatalogus (Jongmans &Dijkstra, 1963;Dijkstra & VanAmerom, 1985)will
betreated.
3. Protodrynaria takhtajanii Vikulinet Bobrov
Thisnew, forthepresent monotypic genus (Vikulin &Bobrov, 1987) hasbeen
based on afossilfound in 1982-83by Vikulinin thePaleogene (UpperEocene-
LowerOligocene) ofTim, c. 450 km south ofMoscow.It consists ofafernfrond
fragment. The description ofthegenusreads: 'Rachis very strong,fronds pinnate,
with deep sinuses. Soriround, placed between theveinsin a doublerow onboth
sidesofthepinna's mainvein.Nervaturedrynarioid,secondorderveinsveryprom-
inent.' The presenceofany spores or sporangia is not mentioned.The new fossil
species is compared withtherecent species Drynariamollis, D.sinica, D.propinqua,
D. quercifolia, andCrypsinus laciniatus.For comparison, only themacromorphol-
ogy ofthefrondandtheshape andplacementofthesorihasbeenused. Unfortunately,
the authors didnot yethaveRoos (1986)attheirdisposal, which isthe mostrecent
monograph ofthe drynarioid ferns.Withoutfurtherdetailson venationandspores,
this fossil couldalso beplaced in thegenusSelliguea (including Crypsinus), on
which Hovenkamp is preparinga monograph.
SPORAE DISPERSAE
Introduction
Theneedtoname dispersed sporesmaypose severeproblems tothepalaeobotanist.
A strict morphographic approach seems tobeindicated,although speculation on the
plant thatproduced thespores is necessary inorder toestablish theirplace in the
naturalsystem oftheplantkingdom as soonandas accurately as possible. Once a
resemblancebetween aspora dispersa andaRecent (orFossil) taxon has beenpub-
lished,itis difficultto reappraise such a claim.However, as aresult ofthe more
general useofSEM(scanning electronmicroscopy), especially incombinationwith
TEM (transmissionelectron microscopy) observations, many'resemblances' indi-
catedmayturn out tobe so slightasto beofnotaxonomicconsequence.Therecent
publication of standardworks on the sporesofRecentferns andtheirallieshave
greatly facilitatedcomparison. Recentpolypodiaceous fernsporeshavebeentreated
lately inthefollowingpublications, whichalsoincludeSEMpictures: Lloyd (1981,
Polypodium), Tryon & Tryon (1982, ferns and fem-allies), Van Uffelen &
Hennipman (1985, Pyrrosia), Hennipman (1990, Polypodiaceae), Tryon& Lugar-
don(1991, fernsand fern-allies,alsowithTEM).
262 BLUMEA VOL. 36,No. 1, 1991
Exospore and perispore
Theexospore('exine') is definedas 'the mainwallofthesporoderm consisting
ofsporopollenin, including theaperture; homologous to exine'by Tryon &Lugar-
don (1991). Lugardon (1971), in hisstudy on theultrastructureofexospore forma-
tion inthehomosporous fems(i.e.,the ordersOphioglossales, Marattiales, Osmun-
dales, andFilicales), states thatallfemsbelonging totheorderFilicales, except for
the Gleicheniaceae, have asimilar type ofexospore, theblechnoidtype, whichis
formedinbasically thesamewayinall sporesofthis type.Therefore,theultrastruc-
tureoftheexospore,anditsformationas studiedwithTEMis ofnouseinidentify-
ing polypodiaceous spores as such, as manyotherfamilieshave the same typeof
exospore ultrastructure.However,variationsinexospore morphology dooccur,and
the ultrastructureofthemature exospore maybe diagnostic ona generic or supra-
generic level (see e.g. Hennipman, 1990,and Tryon & Lugardon, 1991).More-
over,exospore surfacepatterns showmuchvariation,not only inmature spores,but
also duringsporogenesis. Thevariationin mature sporeshas beenobviousfromthe
firstLMstudiesonward,but SEMhas enabledpalynologists to makeacloserstudy
ofthesurface patternsofbothexospore ('exine') andperispore ('perine') in mature
spores(Tryon& Tryon, 1982;Tryon &Lugardon, 1991).
Recently ithas becomefeasibleto study thesuccession ofpatterns during exo-
spore deposition withSEM (Van Uffelen, 1990). Such astudy ofsurfacepatterns
during sporogenesis in severalRecent species ofPolypodiaceae hasshownthat,
apartfromdifferencesinspore shape andsize,differentpatterns succeedeachother,
whilethisontogenetic seriesofpatternsis characteristicona(sub)generic or supra-
generic level(VanUffelen, 1987, 1990).Potonid(1962)already indicatedthatim-
mature sporesas often foundinclosed sporangia ('in situ') may lookvery different
from sporae dispersae ofthesamespecies, whichusually havebeenshedspontane-
ously fromripe sporangia. Thismaybe causedeitherby theabsenceofoneor more
ofthelast-deposited exosporelayers,orby theabsenceoftheperisporeonthespores
'in situ'. Itmayalsobe theresultoftheloss oftheperispore layerduringfossili-
zationofsporaedispersae.
Thepresence ofatrue perisporein Recent ferns, definedby Tryon & Lugardon
(1991)as 'theouter wallofthesporoderm consisting ofmaterialdistinctfromthe
exospore sporopollenin, andformedlaterthan theexospore', hasbeena matterof
debateovertheyears. However,TEM studies(Lugardon, 1978) haveshownthatall
fernsporesandmostsporesofthefem-alliesdo haveaperispore, albeitsometimesa
very thinandinconspicuous one,andthereforevisibleonlyonTEMsections. Inthe
lightofthesefairlyrecentfindings, thepossibility of aperispore stillbeing presentin
Fossil spores shouldbereconsidered.
Variability
Ontheonehand,sporesurfacepatternsinoneRecentspecies offemsmayexhibit
aratherlargevariation,especially inthesizeandspacingofperisporeelements(e.g.,
in Drynaria sparsisora, VanUffelen, 1990,or inseveral species ofPyrrosia, Van
Uffelen& Hennipman, 1985).InthestudyofFossil sporaedispersae itis difficultto