Diversity of exine structure in Upper Carboniferous (Westphalian) selaginellalean megaspores

Studies of wall structure in Mesozoic and Recent selaginellalean megaspores have been well documented. However, Palaeozoic examples have received minimal attention. The principal Palaeozoic megaspore genus of likely selaginellalean affinity is Triangulatisporites, extending from the Upper Devonian to the Upper Carboniferous. The particulate wall ultrastructure of a previously published Carboniferous (Duckmantian) megaspore assigned to this genus suggested that this form of wall construction may have been the ancestral wall structure of the group, an observation which posed difficulties in relating selaginellalean ultrastructure to that of other contemporaneous lycopsid megaspores. Subsequent investigation showed that the genus also contains more laminate exines similar to those of other extinct lycopsids and extant Selaginella species. Our new examples of Triangulatisporites ultrastructure from the Langsettian, Duckmantian and Westphalian D yield more information regarding early variation of wall structure within Carboniferous selaginellalean megaspores and suggest that a more laminate wall composition is at least as old as the particulate form. However, without further investigation of Lower Carboniferous forms, we are unable to state which is indeed ancestral. The laminate structure reported here and elsewhere is, none the less, more easily related to comparable ultrastructure in other groups of Carboniferous lycopsid megaspores and could suggest a link with such genera as Zonalesporites and early Lagenicula. This would be in keeping with current concepts regarding the most primitive ultrastructural type within lycopsid megaspore walls.     

Reworked carboniferous spores: An example from the lower jurassic of northeast Scotland

An association of contemporaneous Jurassic mega- and miospores with reworked Carboniferous mega- and miospores is described from the Lower Lias rocks of northeast Scotland. The assemblage is compared with other accounts of reworked spores in Jurassic sediments. It is suggested that such reworking was particularly common in the Lower Jurassic of northern Europe and that four situations exist in the literature concerning probable cases of reworking: (1) the spores are recognised as reworked; (2) the identity of the spores as Carboniferous species is recognised and the “range” of these species is extended into the Jurassic; (3) the reworked spores are not recognised as such, and are incorrectly assigned to Jurassic genera and species; (4) the spores are recognised as Carboniferous, but their origin is attributed to contamination rather than reworking. In conclusion, the contrasting preservational features exhibited by the reworking and contemporaneous megaspores are discussed and interpreted as the result of differing depositional and postdepositional histories.     

中国四种卷柏科植物孢子的形态观察

利用光学显微镜和扫描电子显微镜对睫毛卷柏（Selaginella ciliaris (Retz.) Spring）、甘肃卷柏（S.kansuensis Ching）、墨脱卷柏（S.mutensis Ching）、毛枝卷柏（S.trichoclada Alston）等4种中国产卷柏科（Selaginellaceae）植物的大、小孢子进行了详细的观察。结果表明,4种卷柏的大、小孢子在表面纹饰方面存在明显的差异,而在每一种内,孢子形态是基本稳定的。因此,孢子形态特征可以作为区分种的重要依据。4种卷柏的大、小孢子的孢壁多为混合纹饰类型,且近极面纹饰比远极面的细密。     

Pteridophytic features in some Lower Carboniferous seed megaspores

Some Lower Carboniferous seed megaspores have triradiate sutures–unequivocal evidence of their being arranged in a tetrahedral configuration. This type of tetrad arrangement is unknown in the ovules of modern gymnospermS. Some of the fossil tetrads consist of one large functional megaspore and three smaller abortive spores attached at the apex of the large one. All four spores have an exinous covering.
Spores arranged in tetrahedral tetrads, and hence with triradiate sutures, are characteristic of many modern and fossil free-sporing pteridophyteS. In possessing this feature the fossil seed megaspores are more similar to the spores of these pteridophytes than to the megaspores of modern gymnosperms.     

中国四种卷柏科植物孢子的形态观察

利用光学显微镜和扫描电子显微镜对睫毛卷柏(Selaginella ciliaris(Retz.)Spring)、甘肃卷柏(S.kansuensis Ching)、墨脱卷柏(S.mutensis Ching)、毛枝卷柏(S.trichoclada Alston)等4种中国产卷柏科(Selaginellaceae)植物的大、小孢子进行了详细的观察.结果表明,4种卷柏的大、小孢子在表面纹饰方面存在明显的差异,而在每一种内,孢子形态是基本稳定的.因此,孢子形态特征可以作为区分种的重要依据.4种卷柏的大、小孢子的孢壁多为混合纹饰类型,且近极面纹饰比远极面的细密.     

On the Megaspores of Four Species of Lepidostrobus

This paper is an account of the megaspores borne by four speciesof Carboniferous Lycopod cones, referred to the genus Lepidostrobus.The megaspores (assigned to the genus Triletes) have been knownisolated for more than twenty years, but the identities of theirparent cone species have not previously been established. Thisstudy suggests the limits of variation that can reasonably beallowed in a ‘spore species’. Three of the conespecies are emended in the light of their spore content, anda new species (Lepidostrobus allantonensis) is described. Usingthe megaspores as a diagnostic cone character, it has provedpossible to correlate a species of isolated cone (Lepidostrobusdudius Binney) with the tree which bore it (Lepidodendron smileKidst.). A cone previously attributed on doubtful evidence toBothrodendron is shown to bear megaspores indistinguishablefrom those of a species reliably attributed to Lepidodendron,suggesting that the attribution to Bothrodendron is incorrect.     

LYCOSPORA FROM CARBONIFEROUS LEPIDOSTROBUS COMPRESSIONS

Spores were extracted from Carboniferous Lepidostrobus compressions in order to associate in situ microspores with dispersed species of Lycospora. Two hundred twenty-six cones were examined, of which 61 contained spores. Fertile cones came from the Westphalian D of England, Namurian B through Westphalian D of the Appalachian and Illinois basins, and the Westphalian D of the Western Interior. Cones were separated into species based on microspore and cone morphology. Lycospora trigonoreticulata was produced by Lepidostrobus princeps from Westphalian C-D rocks from Missouri, the Illinois Basin, and the Appalachian Basin. Lycospora rotunda was produced by Lepidostrobus sp. A from Westphalian A rocks of Alabama. Two cone species produced Lycospora torquifer: Lepidostrobus praelongus from the Westphalian D of Pennsylvania and Lepidostrobus variabilis from the Westphalian A and C of the Illinois and Appalachian basins. Lycospora punctata was produced by Lepidostrobus cf. squarrosus from the Westphalian D of England, the Appalachian Basin, and Illinois Basin. Lycospora noctuina was produced by Lepidostrobus haslingdenensis from the Namurian B/C of Illinois. Microspore species are differentiated primarily on the basis of size, cingulum structure and width, and ornamentation. Cone species differ in width and distal lamina size, shape, and attitude. Lycospora species isolated from clastic species of Lepidostrobus differ completely from those of coal-swamp species, confirming that lycopod trees from clastic environments represent biologically different species from those centered in coal swamps.     

云南产8种卷柏科植物的孢子形态

利用光学显微镜和扫描电子显微镜首次观察了云南产8种卷柏科(Selaginellaceae)植物：钝叶卷柏Selaginella amblyphylla Alston;双沟卷柏S．bisulcata Spring;勃固卷柏S．kwrzii Baker;疏穗卷柏S．laxistrobilis K．H．Shing;微齿钝叶卷柏S．ormata(Hook．et Grev．)Spring;耳叶卷柏S．pseudopaleifera Hand.-Mazz;高雄卷柏S．repanda（Desv．ex Poir)Spring;泰国卷柏S．siamensis Hieron．的大、小孢子形态。研究结果表明卷柏科植物大、小孢子为辐射对称、三裂缝,其表面纹饰复杂,8种卷柏植物的大、小孢子在孢壁纹饰上存在着较明显差异。为卷柏科形态学和系统演化的研究提供了有价值的基础资料。     

Developmental Mechanisms in Heterospory: Features of Post-meiotic Regression in Selaginella

Post-meiotic regression in the sporangia of Selaginella sulcataresults in tetrads comprising small and large spores. From germinationtests it has been found that the small spores are abortive andthe large ones fertile, a circumstance which suggests an innateconstitutional difference between them. Densitomctric measurementsshow that the cytoplasm in the prophase megasporocyte is polarized.At cytokinesis this cytoplasm is simultaneously partitionedinto four cells, equal in size, but presumably not in composition.Initially, all four megaspores in the tetrad grow at the samerate, but later, development becomes differential with one,or more usually two spores increasing rapidly in size and theothers much more slowly. The onset of this phase is signalledby a difference in protoplasmic staining and it is the megasporeswith a densely-staining protoplast which develop to fertility. A comparable process of regression occurs also in the microsporangium;the spores develop differentially after a period of equal growth.Examination of young microspore tetrads shows that daughterspores differ in the density of free cytoplasmic ribosomes.It is suggested that this is a consequence of cither disproportionateinheritance of ribosomes from the parental cell resulting frompolarization or, more probably, since the deficiency is notre-dressed in later development, an inherited difference inthe ability to effect ribosome synthesis after prophase elimination.Endoplasmic reticulum-ribosome complexes, in other organismsbelieved to be implicated in cell degeneration, o0ccur in themicrospore cytoplasm.     

Morphological diversity of the exine sculpture of some Frasnian spores from the northern Timan: Applications for taxonomy and significance for spore dispersal

Microspores and megaspores from micro-and megasporangia of a Late Frasnian plant from the northern Timan are identified as the genus Cristatisporites and Ancyrospora, respectively. The exine sculpture is studied in in situ spores, as well as in dispersed miospores of Cristatisporites, Ancyrospora, and Hystricosporites, found in the rock enclosing the plant. The use of exine appendages as a generic level character is proposed. The shape of appendage extremities and the presence of irregular holes in the exine that are considered to be probable insect feeding damage, allowing us to consider wingless insects as main dispersal agents of the spores.     

Selaginella lakkidiana sp. nov. (Selaginellaceae) from India

Selaginella lakkidiana Nisha, Nampy & Joby sp. nov. from Lakkidi, the Western Ghats of India is described and illustrated. The new species is closely allied to S. chrysorrhizos Spring, but differs by a serrate and smaller sporophyll, smooth megaspores, and reddish brown and pitted microspores.     

ACHLAMYDOCARPON VARIUS COMB. NOV.: MORPHOLOGY AND REPRODUCTIVE BIOLOGY

Structurally preserved arborescent lycopsid fructifications are described from Pennsylvanian age strata in eastern Kentucky and southern Illinois. Achlamydocarpon varius comb. nov. is the name proposed for these cones and previously reported isolated megasporophylls described as Lepidostrobophyllum varius. The specimens range up to 3.5 cm long and represent cone apices. Megasporophylls are spirally arranged and attached to the cone axis at an acute angle. Megasporangia are large with a wall two cell layers thick. Each sporangium contains one large, presumably functional megaspore, and three smaller, abortive megaspores. Functional and abortive spores possess a prominent apical tuft (massa) that covers up to one-third of the proximal surface of the spore. Sporoderm ultrastructure is detailed together with a comparison of morphologically similar sporae dispersae megaspores. The possible function of the megaspore massa is discussed as it relates to the reproductive biology of the cone.     

Experimental modelling of exine self-assembly

Living and fossil megaspores produced by Selaginella (Lycopsida) and its extinct ancestors form distinctive (and occasionally iridescent) exines. Ultrastructural studies of these spores have provided data that demonstrate a colloidal mode of development which in turn implies a degree of self-assembly in the construction of these exines. We present here experimental evidence in support of the theory of selaginellalean megaspore exine construction by depletion flocculation. Iridescent colloidal flocculations of polystyrene latex particles demonstrate an ultrastructural organization virtually indistinguishable from that of the biological system, and clearly demonstrate that self-assembly of complex Selaginella exines by a relatively simple construction process is plausible.     

Ultrastructure and affinity of Lower Carboniferous megaspores from the Moscow Basin, Russia

Ten megaspore species isolated from Moscow Basin lignites of Lower Carboniferous (Viséan) age have been studied by scanning and transmission electron microscopy (SEM and TEM). These species belong to seven megaspore genera: Lagenicula, Sublagenicula, Crassilagenicula, Setosisporites, Zonalesporites, Caudatosporites, and Cystosporites. Megaspores of the genus Caudatosporites have only been described previously from the Duckmantian (Westphalian B); a new species is duly erected. The ultrastructure of megaspore walls from the genera Crassilagenicula and Zonalesporites has not been previously described. This study also places them in context with other contemporaneous megaspores. The study shows that during the Viséan, in the Moscow Basin, megaspores expressed a similar wall ultrastructure despite large differences in external appearance. The genus Crassilagenicula may represent a group of megaspores from plants that had evolved from those bearing gulate megaspores here typified by Lagenicula acuminata, Setosisporites brevispinosus, and Sublagenicula hirsutoida. Zonalesporites brasserti also appears to show affinities to this group, and may be representative of a plant species in a transitional state between the Lagenicula bearing lycopsids and those more isoetalean in nature.     

Teratisms in living and fossil megaspores of the Lycopsida: tetrad arrangement and exine ontogeny

Abnormal megaspore tetrad configurations from Selaginella laevigata and of Lagenicula crass-iaculeata (Lower Carboniferous) have been studied by SEM. These abnormalities reflect the variation expected in the presumed evolution of the seed-plants from free-sporing het-erosporous ancestors. In addition, they indicate a possible role for the aborted members of a tetrad in the successful development and maturation of the functional spore(s). Aborted members of tetrads also reveal the later stages of the developmental sequence occurring in spore wall construction and highlight the interplay of sporopollenin production, its colloidal flocculation and polymerization, and distortion caused by protoplast expansion. Possible causes of abortion in both living and extinct lycopsid megaspores are discussed.     

Lageniastrum macrosporae (fossil Volvocales, Lageniastraceae nov. fam.), an endophyte in megaspores from the Carboniferous of the French Massif Central

Sublagenicula nuda lycophyte megaspores from the upper Visean of central France frequently host a colonial green alga as an endophyte. This association was first recorded more than 100 years ago by the French paleobotanist B. Renault, who introduced the name Lageniastrum macrosporae for the alga. However, the biological significance of the discovery was not fully assessed until recently. The L. macrosporae-S. nuda association represents the oldest compelling fossil evidence for algal endophytes in land plants, and the only example to date of an alga residing in the interior of spores of vascular cryptogams. Here we present a detailed re-evaluation and photographic documentation of the surviving original specimens from the Visean of Combres/Lay and Esnost. Moreover, a newly discovered specimen from the Stephanian of central France represents the first record of this association from the Upper Carboniferous. An emended diagnosis for L. macrosporae Renault, 1896 is provided, and a lectotype and paralectotype are designated. Although L. macrosporae displays a striking suite of morphological characters found in members of the extant chlorophyte family Volvocaceae (especially the genus Volvox), the peculiar biology of the fossil necessitates establishment of a new family, for which the name Lageniastraceae is proposed. Considerations of the adaptive advantages for the alga of occupying the interior of megaspores are offered. These include the possible effectiveness of the spores in protection during periods of desiccation and against plankton-feeding animals, and use of the spores as potential vectors for dispersal from one isolated body of water to another by spore-feeding animals.     

Spores in situ and problems of the classification of Mesozoic tree ferns

Although tree ferns dominated the Mesozoic flora, their taxonomic relationships are poorly understood at the generic level, and next to nothing can be said of evolutionary trends within the group. At least five genera are recognized based on the remains of spore-bearing structures. However, the dispersed spores belong to the same generalized morphotype, and cannot be assigned to genera based on macroscopic remains of fertile leaves. Electron microscopy of spores in situ may partly resolve these problems providing additional criteria for classification of spore-bearing structures and disperse spores. We studied in situ spores of the Early Cretaceous Alsophilites nipponensis (Oishi) Krassilov, which are comparable to dispersed spores Cyathidites minor Coup. Spore wall micromorphology and ultrastructure indicate their affinities with the modern genus Alsophila R. Brown. Only occasional poorly preserved striate sculptures survive the standard treatment of maceration of the perispore. Our data confirm the primitive status of the species with a great number of spores per sporangium, thick unsculptured exospore consisting of two ultrastructural layers, and the possibility that whole sporangia with unshed spores can function as dispersal units.     

Westphalian Sporo-Pollen Assemblages from the Upper Carboniferous in Zhongwei,Ningxia

About 98 species of fossil spores and pollen referred to 55 genera from the Upper Carboniferous Yanghugou Formation in Zhongwei, Ningxia have been studied. Two sporopollen assemblage zones are recognized in ascending order as follows: 1. Laevigatosporites medius-Cyclogranisporites aureus (MA) zone: This assemblage corresponds to the lower part of the Yanghugou Formation, and is characterized by the predominance of pteridophyfic spores and the relative abundance of gymnospermous pollen. Azonotriletes and monoletes are dominant, while zonates are of importance. The most common species are Leiotriletes spp., Cyclogranisporites aureus Potoni6 et Kremp, Granulatisporites granulatus Ibrahim, Microreticulatisporites concavus Butterworth et Williams, M. nobilis (Welcher) Knox, Triquitrites bransonii Wilson et Hoffmeister, Dictyotriletes bireticulatus (Ibrahim) Smith et Butterworth, Ahrensisporites guerickei (Horst) Potonie et Kremp, Lycospora spp., Crassispora kosankei (Potonie et Kremp) Bharadwaj, Cirratriradites saturni (Ibrahim) Schopf, Wilson et Bentall, Laevigatosporites spp., Columinisporites ovalis Peppers, Florinites junior Potnie et Kremp and Vesicaspora wilsonii (Schemel) Wilson et Venkatachata. This assemblage is comparable with those of the Yanghugou Formation in Baiyantaohai of Inner Mongolia (Yu, 1983), the 8th zone of North China by Gao (1979), the Triquitrites sinani-Cirratriradites saturni (SS) Zone and the Microreticulatisporites nobilis-Florinites junior (NJ) Zone of West Europe, which are considered corresponding to Westphatian A-B in age. 2. Torispora seuris-Punctatisporites hians (SH) zone: This assemblage is equivalent to the upper part of the Yanghugou Formation, and is also characterized by dominance of pteridophytic spores and subdominance of gymospermous pollen. In addition to the most commen species mentioned above, the important taxas in the present assemblage comprise Punctatisporites hians Wang, Gulisporites cochlearius Imgrund, Verrucosisporites kaipingiensis Imgrund, Endosporites globiformis (Ibrahim) Schopf, Wilson et Bentall, Densosporites anulatus (Loose) Smith et Butterworth, D. reticuloides Ouyang et Li, Simozonotriletes labellatus Wang, Torispora securis Balme, Thymospora thiessenii (Kosanke) Wilson et Venkatachala, Pit yos porites west phalensis Williams and Plat ysaccus, Illinites, C ycadopites, etc. This zone compares closely with those of the upper part of the Yanghugou Formation in Hengshanbu (Wang Hui, 1984) and Ordos Basin (Geng, 1985), the Benxi Formation in Shanxi (Liao, 1987; Ouyang and Li, 1980; Gao, 1979), as welll as Torispora securis-T, laevigata (SL) Zone and Thymospora obscura-T, thiessenii (OT) Zone of West Europe. Therefore, the present SH Zone should be referred to Westphalian C-D in age. The Westphalian palynofiora in Zhongwei is dominated by Filicopsida and pteridospermopsida; Sphenopsida and lycopsida occupy the subdominant position, while Cordaitopsida and Coniferopsida do not develop well. This palynofiora indicates a tropical-subtropical warm and humid paleoclimate.     

西藏产四种卷柏科植物的孢子形态观察

利用光学显微镜和扫描电子显微镜观察了西藏产4种卷柏科(Selaginellaceae)植物波密卷柏(Selaginella bomiensis Ching et S.K.Wu)、宽叶卷柏(S. megaphylla Baker)、墨脱卷柏(S. mutensis Ching)和钱形卷柏(S. nummularifolia Ching)的大、小孢子形态。扫描电镜观察结果显示：这4种卷柏科植物的孢子具有复杂的外部纹饰特征,且种间有很大的差异,可作为种间鉴别的重要分类依据。4种卷柏的孢子形态均为首次报道,为卷柏科系统演化及形态学研究提供有价值的基础资料。