On a new medullosan pollen organ from the Pennsylvanian of North America

nology 142 (2006) 219–227www.elsevier.com/locate/revpalbo

Review of Palaeobotany and Paly

On a new medullosan pollen organ from thePennsylvanian of North America

Rudolph Serbet a,⁎, Thomas N. Taylor a,b, Edith L. Taylor a,b

a Division of Paleobotany, Natural History Museum and Biodiversity Research Center, University of Kansas, Lawrence, KS 66045, USAb Department of Ecology and Evolutionary Biology, Division of Paleobotany, Natural History Museum and Biodiversity Research Center,

University of Kansas, Lawrence, KS 66045, USA

Available online 28 August 2006

Abstract

Interpreting the reproductive biology of fossil plants has contributed significantly to our understanding of plant evolution. Especiallyimportant are studies that have focused on structurally preserved reproductive organs that contain pollen or spores. AmongCarboniferous pteridosperms, the medullosans are interpreted as a highly diverse group based on a large number of pollen organs andovules. Here we report a permineralized pollen organ of Pennsylvanian age (Breathitt Formation) from eastern Kentucky, USA. Thesynangium is slightlymore than a centimeter long and approximately 2.5mm in diameter, and composed of 10–12 thin-walled, elongatesporangia. Vascular bundles occur in the periphery of the ground tissue. Pollen grains are of theMonoletes-type and up to 195 μm long.When compared with other Monoletes-producing pollen organs, the Lewis Creek synangium is most similar to the impression/compression morphotype Aulacotheca. Based on the co-occurrence of vegetative and reproductive organs, we suggest that this pollenorgan was borne on Medullosa anglica.© 2006 Elsevier B.V. All rights reserved.

Keywords: pollen organ; Pennsylvanian; Medullosales; Monoletes; synangium; seed ferns

1. Introduction

Reproductive structures of fossil plants are an impor-tant source of information necessary to classify extinctplants. This information is also essential in documentingthe biodiversity and evolutionary trends within majorgroups of fossil plants. The medullosan pteridosperms areone of the most diverse groups of fossil seed ferns basedon dispersed reproductive organs and have been docu-

⁎ Corresponding author. Division of Paleobotany, Natural HistoryMuseum and Biodiversity Research Center, University of Kansas,Lawrence, KS 66045, USA.

E-mail addresses: [email protected] (R. Serbet), [email protected](T.N. Taylor), [email protected] (E.L. Taylor).

0034-6667/$ - see front matter © 2006 Elsevier B.V. All rights reserved.doi:10.1016/j.revpalbo.2006.07.001

mented from the Lower Carboniferous into the Permian.The Lewis Creek coal ball assemblage in eastern Ken-tucky represents a diverse flora that includes some ele-ments that have only been reported from LowerPennsylvanian equivalent deposits in Europe (Phillips,1980; Galtier, 1997). Species of medullosan organsknown from this site include Medullosa anglica (Smootand Taylor, 1981) and Pachytesta muncii (Cichan andTaylor, 1981); Alethopteris and Myeloxylon, althoughpresent in abundance at the site, have not been studied todate. The discovery of a new pollen organ from thislocality not only provides the opportunity to expand ourunderstanding of the diversity of synangiate pollenorgans, but also to characterize the components of aPaleozoic seed fern. The occurrence of Monoletes-type

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http://dx.doi.org/10.1016/j.revpalbo.2006.07.001

220 R. Serbet et al. / Review of Palaeobotany and Palynology 142 (2006) 219–227

pollen grainswithin the sporangia indicates that the pollenorgan belongs within the Medullosaceae and is the firstreproductive structure with this type of synangialorganization.

The Lewis Creek coal ball site has yielded a diversearray of fossils that include several taxa of fungi, andrepresentatives of the Sphenophyllales, Equisetales,Lepidodendrales, Zygopteridales, Marattiales, Filicales,

221R. Serbet et al. / Review of Palaeobotany and Palynology 142 (2006) 219–227

Lyginopteridales, Medullosales and Cordaitales. Thisflora has numerous taxa that are also commonly found instratigraphically equivalent Lower Pennsylvanian florasof Europe (Phillips, 1980; Galtier, 1997). The presenceof several of these taxa together with the medullosanelements suggests that this flora is more similar to theEuropean Paleozoic plants then to the well documentedMiddle Pennsylvanian floras of North America.

Numerous pollen organs with varying degrees ofcomplexity have been attributed to the Medullosales(Millay and Taylor, 1979). These include Dolerotheca(Halle, 1933; Schopf, 1948; Dennis and Eggert, 1978;Dufek and Stidd, 1981),Bernaultia (Rothwell and Eggert,1986), Schopfitheca (Delevoryas, 1964), Aulacotheca(White, 1900; Halle, 1933; Jongmans, 1937; Hemingway,1941; Arnold, 1949; Tidwell, 1967; Eggert and Kryder,1969; Mickle and Leary, 1984), Whittleseya (Newberry,1853; Halle, 1933), Codonotheca (Sellards, 1903, 1907;Stidd and Leisman, 1985), Rhetinotheca (Leisman andPeters, 1970; Rothwell and Mickle, 1982), Sullitheca(Stidd et al., 1977), Potoniea (Stidd, 1978; Schultka,1995), Halletheca (Taylor, 1971; Taylor and Millay,1981;Mapes, 1982),Parasporotheca (Dennis and Eggert,1978), Stewartiotheca (Eggert and Rothwell, 1979),Boulayatheca (Taylor and Kurmann, 1985), Goldenber-gia (Halle, 1933) and Saharatheca (Stidd, 1991). It hasbeen suggested that two of these taxa, Parasporotheca,which produced grains with vestigial sacci and Potoniea,with trilete pollen, may not belong to the Medullosaceae(Schopf, 1948; Stidd, 1981; Taylor, 1988). The diversityof medullosan pollen organs may also reflect differingmodes of pollen dispersal, some of which may have beenfacilitated by biotic vectors (Scott and Taylor, 1983).

2. Materials and methods

The pollen organ described here occurs in a calcareouscoal ball from Lewis Creek, Kentucky, and was studiedusing the cellulose acetate peel technique. Peels weremounted on microscope slides with Eukitt mountingmedium; images were captured using a Leica DC500digital camera and processed with Adobe Photoshop.

Plate I.

1. Transverse section of pollen organ showing numerous sporangscale=1.0 mm.

2. Slightly oblique longitudinal section of pollen organ. No. 6559 B3. Longitudinal section of pollen sac (S) containing Monoletes g

scale=0.35 mm.4. Two secretory canals showing opaque contents. No. 6559B bot, N5. Vascular bundle of several tracheids, some with helical–scalarifor6. Transverse section of vascular bundle (arrow). No. 6559 B side, N

Pollen was extracted using melted dental wax to form awell around the pollen sacs (Osborn and Taylor, 1995).Five percent stock hydrochloric acid was used to dissolvethe matrix and the resulting solution of acid and organicmaterial pipetted into distilled water. Subsequent to neu-tralization in distilledwater the isolated pollen grainsweredried and mounted on SEM stubs with two-sided taped,coated with gold and scanned using a LEO 1550 scanningelectron microscope. The coal ball, peels, images andslides are deposited under the acquisition numbers22,432–22,451 in the Division of Paleobotany, NaturalHistory Museum and Biodiversity Research Center, Uni-versity of Kansas collections.

3. Results

3.1. Systematics

Order MedullosalesFamily MedullosaceaeMurielatheca Serbet, Taylor et Taylor gen. nov.Generic diagnosis: Pollen organs elongate, and taper

toward the base with sporangia embedded within acontinuous parenchymatous cortex containing elongatesecretory canals; sporangia are associated with singlevascular strand composed of tracheids with helical–scalariform thickenings; pollen grains monolete withdistal umbo and proximal suture.

Murielatheca delicata Serbet, Taylor et Taylor sp.nov.

Specific diagnosis: Pollen organs at least 1.3 cmlong and 2.5 mm in diameter; synangium of 10–12sporangia, each approximately 0.7 mm in diameter;synangium wall parenchymatous with secretory canalsup to 140 μm in diameter that are variable in length;vascular bundles of tracheids up to 18 μm in diameter;pollen of the Monoletes-type, 144–195 μm long and100–142 μm in equatorial diameter; proximal suture3/4 the length of the grain with slight angulardeflection; pollen wall of outer alveolate sexine upto 10 μm thick and inner homogenous nexine up to2.5 μm thick.

ia (S) filled with Monoletes grains. No. 6559 B side, No. 28. Bar

bot, No. 6. Bar scale=1.5 mm.rains and secretory canals (arrows). No. 6559 B bot, No. 2. Bar

o. 0. Bar scale=145 μm.m thickenings. No. 6559 B bot, No. 6. Bar scale=18 μm.o. 27. Bar scale=15 μm.


Etymology: The generic name Murielatheca isproposed to honor the career and inspiring work inPaleozoic paleobotany of our friend and colleague,Muriel Fairon-Demaret, theca—referring to containerwith pollen; the specific epithet delicata refers to thedelicate nature of the pollen organ.

Holotype: Specimen in coal ball number 6559B side(Slides 13, 15, 18, 22–24, 26–32; B bot. 0–6 (Figs. 1–6in this paper).

Collecting locality: Lewis Creek, Kentucky. Univer-sal Transverse Mercator Grid Coordinates 297,250E4097,500N, Cutchin 7.5′ quadrangle (4 miles east ofChappell town site).

Stratigraphy: Copland (Taylor) Coal, Magoffin Mem-ber, Pottsville Series, Kanawha Equivalent, BreathittFormation.

Age: Middle Pennsylvanian.

Plate II.

1. Proximal surface of pollen grain showing suture with slight media2. Sexine (S) of pollen wall with anastomosing muri. Bar scale=3 μ3. Distal surface of pollen grain showing collapsed umbo. Bar scale4. Homogeneous nexine (N) of pollen grain wall. Bar scale=1.0 μm

3.2. Description

The preserved portion of the pollen organ is cons-tructed of approximately 10 to 12 sporangia fused to forman elongate structure approximately 1.3 cm long and2.5mm in diameter (Plate I, 1, 2). Individual sporangia areapproximately 0.7 mm in diameter and appear to berandomly arranged within a parenchymatous tissue inter-spersed with elongate secretory canals; sporangial ar-rangement may be the result of poor preservation.Secretory canals extend throughout the tissue of theorgan and generally parallel the long axis of the sporangia.In section view they are conspicuous, with some up to132 μm in diameter, and often contain opaque contents(Plate I, 3, 4). In some sections, it is possible to identify avascular bundle in the ground tissue opposite a sporan-gium; however, we are uncertain as to whether each

n deflection. Bar scale=20 μm.m.=20 μm..


sporangium is associated with a vascular strand. Tra-cheids are 10–18μm in diameter with helical–scalariformsecondary wall thickenings (Plate I, 5); there is noinformation as to the nature of the vascular strand at thebase of the organ. Serial peels indicate that the base of thepollen organ tapers to form what we interpret as a slenderstalk. The distal end of the pollen organ appears to narrow,but we are uncertain as to the exact morphology of the tipof the structure.

Sporangia of Murielatheca delicata contain Mono-letes-type pollen grains. They are ellipsoidal and rangefrom 144 to 195 μm long and 100 to 142 μmwide; theseare some of the smallest sizes recorded for Monoletes.The proximal suture extends approximately 3/4 thelength of the grain (Plate II, 1) and contains a slightangular deflection characteristic of mature pollen grainsof this type. On the distal surface are two longitudinalfurrows that extend the length of the grain separated bythe umbo; in some grains, the umbo is sunken andsomewhat distorted (Plate II, 3). The sporoderm isdivided into two distinct layers. The outer sexine isapproximately 10 μm thick and constructed of anasto-mosing muri with closely spaced lumina. Toward theouter surface, lumina become larger and more widelyseparated (Plate II, 2); near the periphery, they becomemore closely spaced. The second component of the wallis the nexine which is up to 2.5 μm thick andhomogeneous (Plate II, 4). These features are charac-teristic of mature Monoletes pollen grains (Taylor andRothwell, 1982). Lamellations of the nexine could notbe determined.

4. Discussion

4.1. Medullosan pollen organ diversity

Medullosan pollen organs have been the focus of anumber of studies that have dealt with their structure anddiversity through time and attempted to place the variousforms within an evolutionary context (Millay and Taylor,1979; Stidd, 1981; Taylor, 1988). As a result of thenumerous pollen organ morphologies, the medullosansare recognized as the most diverse group of pterido-sperms. Although numerous permineralized and com-pression/impression fossils of pollen organs, ovules,petioles and stems have been described, relatively feworgans have been found attached in sufficient detail toprovide taxonomic resolution useful in whole plantreconstructions.One study of the impression/compressiontaxon Aulacotheca iowensis indicates that in this speciesthe pollen organs were borne in clusters on planatedbranching systems (Eggert and Kryder, 1969). Whether

the pollen organs were borne on vegetative fronds, in theplace of fronds, or occurred between rachides of a bifur-cating frond continues to remain unknown. Other pollenorgans within the Medullosaceae, such as Bernaultia,were borne on fronds in the place of a penultimate pinna(Ramanujam et al., 1974). Although some pollen organswere borne singly, others likeRhetinothecawere arrangedin clusters (Leisman and Peters, 1970). In Rhetinotheca,the individual synangia were covered by specializedtrichomes which were interlocked with trichomes ofadjacent synangia to form large compound aggregations.In addition to their site of attachment on the plant, there isanother level of diversity relating to the structural orga-nization of the synangia. Based on permineralized forms,it has been suggested that there are multiple patterns ofstructural organization for the medullosan pollen organs(Millay and Taylor, 1979; Taylor, 1988).

One of the three basic types of medullosan pollenorgans is exemplified by the Codonotheca type (Millayand Taylor, 1979). In this simple type, the sporangia arearranged in a ring with the individual pollen sacs fused inthe proximal third of the organ (Sellards, 1903, 1907).This structural organization has been interpreted as an-cestral to several other types of medullosan pollen organs(Stidd, 1981; Taylor, 1988). This evolutionary scenariomay be tempered, however, by the fact that Aulacotheca,a pollen organ with individual pollen sacs fused for theirentire lengths, occurs earlier in the fossil record (Na-murian) than the late Westphalian appearance of Codo-notheca (Stidd, 1981). Another modification of thissimple pattern occurs in Whittleseya, where the entiresynangium is larger and includes many more pollen sacsthat surround a central hollow. A similar pattern occurs inParasporotheca, but at maturity this synangium is bila-terally symmetrical and contains pollen that is distinctlydifferent from theMonoletes grains which characterize allother medullosan pollen organs.

Another simple medullosan pollen organ is Aulaco-theca, a genus which includes the largest number ofspecies. In this taxon, sporangia are fused laterally to forma ring-like structure around a central hollow region (Halle,1933). Boulayatheca, another simple form, is character-ized by sporangia embedded within a ground tissue andarranged around a central hollow core. Some simpleforms such as Boulayatheca, Goldenbergia and Schop-fitheca may represent different pollen organ types, vary-ing preservational states and levels of synangiumdevelopment. In Halletheca (Taylor, 1971), sporangiaare embedded within a simple ground tissue and arrangedin a ring around a central core of sclerenchymatous tissue.The central column extends for approximately half thelength of the synangium and, as the organ matures, the

Fig. 1. Idealized reconstruction of Murielatheca delicata showingsporangia containing pollen. Pollen not to scale. Central region hypothe-tical. Bar scale=1 mm.


sclerenchymatous core splits, which has been interpretedas a mechanism for pollen dispersal (Taylor and Millay,1981). Saharatheca lobata also has a central core ofsclerenchymatous tissue, but in this species the core isbilobed–trilobed. This tissue is solid toward the base ofthe pollen organ but distally may become subdivided(Stidd, 1991). The distal end is not preserved and pollendispersal may have been facilitated as in Halletheca,through the distal end of the organ. A solid central core oftissue is also present in both species of Rhetinotheca. InR. patens, the central column intergrades with dehiscencetissue to facilitate dispersal of pollen (Rothwell andMickle, 1982). In R. tetrasolenata, it is not knownwhether pollen dispersal depends on the organization ofthe central column (Leisman and Peters, 1970). An addi-tional pattern of the simple type is seen in Murielatheca,where pollen sacs are embedded in a ground tissue that ishistologically identical to the central core of the synangiumFig. 1).

Both the second and third types of medullosan pollenorgans are larger and campanulate in their morphology(Schopf, 1948), consisting of numerous pollen sacswhich appear in cross section to radiate outward from acentral point. The second type includes simple unitswhich are not highly folded and which exhibit a distalhollow area surrounding a central hollow area. An in-creased number of plications, which results in moresporangia per unit, is a characteristic of Stewartiotheca.Here the synangium also contains a central sclerenchy-matous core that becomes hollow toward the distal endof the organ.

The third type of pollen organ lacks a central hollowcore; pollen was probably dispersed from the distal end.These forms can be simple or complex, with the complexforms consisting of multiple simple units that are highlyplicated and embedded in a common ground tissue. Todate, the largest medullosan pollen organ is Dolerotheca(Schopf, 1948), which can be up to 4.0 cm in diameter.Historically, this synangium was interpreted as a tightlycompacted aggregation of elongate pollen sacs, but Dennisand Eggert (1978) reinterpreted the basic organization as ahighly plicated pollen organ composed of multiple units,each unit corresponding to a single synangium. Rothwelland Eggert (1986) reviewed the campanulate pollen organsand erected a new genus, Bernaultia, for those forms inwhich external morphology and internal organization areknown. They retainedDolerotheca for campanulate organsthat are poorly known. The most complex forms of Ber-naultia include four plicated synangial units that are fusedto form the large campanulum.

The presence of Monoletes-type grains within Murie-latheca indicates that the Lewis Creek pollen organ has

medullosan affinities. Morphologically, Murielatheca ismost comparable to the impression/compression taxonAulacotheca in both size and shape, and in the type ofpollen, and may represent a permineralized synangium ofthe Aulacotheca-type. However, as noted by Halle (1933)and others, Aulacotheca pollen organs consist of a ring ofclosely appressed sporangia in which the central area ishollow. The structure of the Murielatheca synangiumindicates, however, that the individual sporangia are em-bedded in a parenchymatous ground tissue containingelongate secretory canals (Fig. 2). This type of sporangialorganization would placeMurielatheca delicata as one ofthe simple-types, but differs in lacking either a solidcentral core of specialized cells as in Halletheca, or acentral region that is hollow (e.g., Goldenbergia). Thepossibility exists that, as pollen organs matured, cells ofthe central tissues broke down so that pollen release was


toward the center of the synangium (Taylor, 1988). If sucha developmental pattern occurred, then a mature synan-gium of the Murielatheca-type preserved as an impres-sion/compression would be quite similar to Aulacotheca.Although the Monoletes grains found in M. delicata aresome of the smallest of any medullosan pollen describedto date, there is some overlap with those of several speciesof Aulacotheca.

Although some have suggested evolutionary patternsin medullosan pollen organs that have involved an in-crease in the number of pollen sacs and size of thesynangia, we are uncertain as to the validity of thesepatterns within a phylogenetic context. There does,however, appear to be some correlation between thesimple synangiate forms and their stratigraphic distri-bution. For example, Murielatheca occurs in the lowerportion of the Middle Pennsylvanian and Aulacothecais found in Lower Pennsylvanian rocks in Europe,while the more complex types appear to be stratigra-phically younger.

4.2. Medullosa anglica plant

One of the unusual aspects of the permineralizedassemblage from Lewis Creek, Kentucky is the presenceof a number of plants that are unknown from other Penn-sylvanian coal ball localities in North America (Phillips,1980). These include the sphenophyte cones,Bowmanitesdawsonii (Taylor, 1969) and Calamostachys binneyana(Taylor, 1967), and the cordaitean seed, Mitrospermumcompressum (Taylor and Stewart, 1964). The occurrencesof these taxa in the Lewis Creek deposits suggest that thiscoal ball assemblage comparable to with the LowerPennsylvanian coal balls of Europe. Medullosan seed

Fig. 2. Transverse section of Murielatheca delicata at approximate midleveblack ellipses. Bar scale=1 mm.

ferns at this site are represented by Medullosa anglica(Smoot and Taylor, 1981) and Alethopteris and Myelox-ylon petioles, but these latter taxa have not been studied todate. With the discovery of the pollen organ Murie-latheca delicata from this locality and the lack of anyother medullosan plant organs, we suggest that theseorgans probably represent parts of the same plant. Au-lacotheca pollen organs, and foliage and petioles ofAlethopteris and Myeloxylon are also widespread in theLower Pennsylvanian sites in Europe. The Europeansites, however, contain the seed Pachytesta olivaeformiswhich is unknown from Lewis Creek. It does not appearthat P. olivaeformis and Pachytesta muncii representdifferent developmental stages of the same species. It isinteresting, however, that secretory canals somewhatsimilar to those in Murielatheca have been reported inthe integument of P. muncii (Cichan and Taylor, 1981).This may be of little systematic importance since nearlyall medullosan seed fern parts possess secretory cellsand/or canals.

Pollen organ diversity is greatest among the medul-losan seed ferns and identification of organs belonging tothis group is made easier because of the distinctive sizeand morphology ofMonoletes pollen grains. There is alsoconsiderable variability in the structure of the seeds attri-buted to the medullosan seed ferns which parallels thatknown for the pollen organs. While there are numerousspecies of foliage that are thought to have been borne bymedullosan seed ferns, there are only a few species ofstems known. Moreover, detailed anatomical studies ofthe stems suggest little variability and few definitive cha-racters that might be useful in identifying reproductiveorgan/vegetative organ relationships. Despite these obsta-cles, the correlation of permineralized floral components

l (horizontal lines of Fig. 1). Position of secretory canals indicated by


within and between stratigraphic sites provides the oppor-tunity to assemble the isolated organs of Paleozoic plantswith some degree of confidence. Our interpretation of theorgan affinities used to reconstruct theMedullosa anglicaplant represent a starting point inmore accurately definingone of the medullosan seed ferns. Such reconstructionsare critical if phylogenetic analyses of major groups likethe medullosans are to be robust and contribute to under-standing the position of pteridosperms in the evolution ofseed plants.

Acknowledgments

This paper was prepared to honor the distinguishedcareer of Professor Muriel Fairon-Demaret. This studywas supported by National Science Foundation grantOPP-0229877. We thank Gilbert J. Ortiz for preparingFigs. 1 and 2.

References

Arnold, C.A., 1949. Fossil flora of the Michigan coal basin. Contrib.Mus. Paleontol. Univ. Mich. 7, 131–269.

Cichan, M.A., Taylor, T.N., 1981. On the structure and morphology ofthe seed Pachytesta muncii n. sp. (Medullosales). Rev. Palaeobot.Palynol. 34, 359–367.

Delevoryas, T., 1964. A probable pteridosperm microsporangiatefructification from the Pennsylvanian of Illinois. Palaeontology 7,60–63.

Dennis, R.L., Eggert, D.A., 1978. Parasporotheca gen. nov., and itsbearing on the interpretation of the morphology of permineralizedmedullosan pollen organs. Bot. Gaz. 139, 117–139.

Dufek, D., Stidd, B.M., 1981. The vascular system of Dolerotheca andits phylogenetic significance. Am. J. Bot. 68, 897–907.

Eggert, D.A., Kryder, R.W., 1969. A new species of Aulacotheca(Pteridospermales) from the Middle Pennsylvanian of Iowa. Palaeon-tology 12, 414–419.

Eggert, D.A., Rothwell, G.W., 1979. Stewartiotheca gen. n. and thenature and origin of complex permineralized medullosan pollenorgans. Am. J. Bot. 66, 851–866.

Galtier, J., 1997. Coal-ball floras of the Namurian-Westphalian ofEurope. Rev. Palaeobot. Palynol. 95, 51–72.

Halle, T.G., 1933. The structure of certain fossil spore-bearing organsbelieved to belong to pteridosperms. K. Sven. Vetensk.Akad. Handl.,Ser. 3 (12), 1–103.

Hemingway, W., 1941. On the coal-measure plant, Aulacotheca. Ann.Bot., N.S. 5, 197–201.

Jongmans, W., 1937. Comparisons of the floral succession in theCarboniferous of West Virginia with Europe. Compt. Rend. 2eme

Congr. Strat. Carb. Heerlen, vol. 1, pp. 393–415.Leisman, G.A., Peters, J.S., 1970. A new pteridosperm male

fructification from the Middle Pennsylvanian of Illinois. Am. J.Bot. 57, 867–873.

Mapes, G., 1982. Halletheca conica, medullosan synangia from theWewoka Formation in Oklahoma. Bot. Gaz. 143, 125–133.

Mickle, J.E., Leary, R.L., 1984. Aulacotheca collicola n. sp. (Medullosa-ceae) from the Early Pennsylvanian of the Illinois basin. Rev.Palaeobot. Palynol. 43, 343–357.

Millay, M.A., Taylor, T.N., 1979. Paleozoic seed fern pollen organs.Bot. Rev. 45, 301–375.

Newberry, J.A., 1853. Fossil plants from the Ohio Coal Basin. Ann.Sci. 1 (95–97), 106–108.

Osborn, J.M., Taylor, T.N., 1995. Pollen morphology and ultrastruc-ture of the Bennettitales: in situ pollen of Cycadeoidea. Am. J. Bot.82, 1074–1081.

Phillips, T.L., 1980. Stratigraphic and geographic occurrences ofpermineralized coal-swamp plants—Upper Carboniferous of NorthAmerica and Europe. In: Dilcher, D.L., Taylor, T.N. (Eds.), Biostra-tigraphy of Fossil Plants. Dowden, Huttchinson and Ross Inc.,Stroudsburg, Pa., pp. 25–92.

Ramanujam, C.G.K., Rothwell, G.W., Stewart, W.N., 1974. Probableattachment of the Dolerotheca campanulum to a Myeloxylon–Alethopteris type frond. Am. J. Bot. 61, 1057–1066.

Rothwell, G.W., Eggert, D.A., 1986. A monograph of DolerothecaHalle, and related complex permineralised medullosan pollenorgans. Trans. R. Soc. Edinb. Earth Sci. 77, 47–79.

Rothwell, G.W., Mickle, J.E., 1982. Rhetinotheca patens n. sp., amedullosan pollen organ from the Upper Pennsylvanian of NorthAmerica. Rev. Palaeobot. Palynol. 36, 361–374.

Schopf, J.M., 1948. Pteridosperm fructifications: American species ofDolerotheca, with notes regarding certain allied forms. J. Paleontol.22, 681–724.

Schultka, S., 1995. The Carboniferous pollen organ Potoniea: pinnatefrond organization. Rev. Palaeobot. Palynol. 89, 297–303.

Scott, A.C., Taylor, T.N., 1983. Plant/animal interactions during theUpper Carboniferous. Bot. Rev. 49, 259–307.

Sellards, E.H., 1903. Codonotheca, a new type of spore bearing organfrom the coal measures. Am. J. Sci. 16, 87–95.

Sellards, E.H., 1907. Notes on the spore bearing organCodonotheca andits relationship with the Cycadofilices. New Phytol. 6, 175–178.

Smoot, E.L., Taylor, T.N., 1981. The petrified pteridosperm stem Me-dullosa anglica from the Pennsylvanian of North America. Palaeon-tology 24, 647–653.

Stidd, B.M., 1978. An anatomically preserved Potoniea with in situspores from the Pennsylvanian of Illinois. Am. J. Bot. 65, 677–683.

Stidd, B.M., 1981. The current status of medullosan seed ferns. Rev.Palaeobot. Palynol. 32, 63–101.

Stidd, B.M., 1991. Saharatheca lobata n. gen. and sp.: a newmedullosan(seed fern) pollen organ from the Middle Pennsylvanian of Illinois.J. Paleont. 65, 160–166.

Stidd, B.M., Leisman, G.A., 1985. A new species of Codonotheca(Medullosaceae, Pteridospermales) from theUpper Pennsylvanian ofKansas. In: Dutro Jr., J.T., Pfefferkorn, H.W. (Eds.), Compt. Rend.9th Int. Congr. Strat. Géol. Carbonifère (Champaign-Urbana, IL.,1979). Paleontology, Paleoecology, Paleogeography, vol. 5. SouthernIllinois University Press, Carbondale, pp. 155–158.

Stidd, B.M., Leisman, G.A., Phillips, T.L., 1977. Sullitheca dactyliferagen. et sp. n.: a new medullosan pollen organ and its evolutionarysignificance. Am. J. Bot. 64, 994–1002.

Taylor, T.N., 1967. On the structure ofCalamostachys binneyana from theLower Pennsylvanian of North America. Am. J. Bot. 54, 298–305.

Taylor, T.N., 1969. On the structure of Bowmanites dawsoni from theLower Pennsylvanian of North America. Palaeontographica 125B,65–72.

Taylor, T.N., 1971. Halletheca reticulatus gen. et. sp. n.: a synangiatePennsylvanian pteridosperm pollen organ. Am. J. Bot. 58, 300–308.

Taylor, T.N., 1988. Pollen and pollen organs of fossil gymnosperms:phylogeny and reproductive biology. In: Beck, C.B. (Ed.), Origin andEvolution of Gymnosperms. Columbia University Press, New York,pp. 177–217.


Taylor, T.N., Millay, M.A., 1981. Additional information on the pollenorgan Halletheca (Medullosales). Am. J. Bot. 68, 1403–1407.

Taylor, T.N., Kurmann, M.H., 1985. Boulayatheca, the new name forthe seed fern organ Boulaya. Taxon 34, 666–667.

Taylor, T.N., Stewart, W.N., 1964. The Paleozoic seed Mitrospermumin American coal balls. Palaeontographica 115B, 50–58.

Taylor, T.N., Rothwell, G.W., 1982. Studies of seed fern pollen:development of the exine in Monoletes (Medullosales). Am. J. Bot.69, 570–578.

Tidwell, W.D., 1967. Flora of Manning Canyon shale: I. A lowermostPennsylvanian flora from the Manning Canyon shale, Utah, and itsstratigraphic significance. Brigham Young. Univ. Geol. Stud. 14,3–66.

White, D., 1900. The stratigraphic succession of the fossil floras of thePottsville Formation in the southern anthracite coal field of Penn-sylvania. U.S. Geol. Surv. Ann. Rep. 20, 749–930.

Documents

On a new medullosan pollen organ from the Pennsylvanian of North America