Ab strA ct The genus Mariopteris ZEILLER is distributed from the Namurian A to the early Stephanian in Europe. In the ­Dobrudzha­Basin,­numerous­specimens­are­found­mainly­in­flood­plain­claystones­and­siltstones.­The­habitat­and­ reconstruction­of­the­plants­suggests­a­creeping­manner­of­growth.­Climatic­changes­are­reflected­in­the­architecture­ of­species.­One­specimen­has­an­attached­seed­proving­the­classification­of­the­genus­as­a­pteridosperm. Keywords: Mariopteris, pteridosperm, creeping plant, attached seed 1. IntroductIon The genus Mariopteris has attracted the attention of many palaeobotanists. ZEILLER (1878, 1879) created this genus that is now known to embrace species that were referred to different genera. Many monographs (HUTH, CORSIN, DANZE-CORSIN, BOERSMA), and part-authors of large monographs (ZEILLER, STUR, GOTHAN, KIDSTON dates needed here too), and other articles concern these plants.­While­the­architecture,­classification,­taxonomy,­syn- onymy and species diversity are frequently discussed, the habitat of this group is rather poorly considered. It is ac- cepted that they are probably creeping, intertwining or climbing, in habit. 2. PlAnt elements And termInology BOERSMA (1972, p. 24) used the term “frond” for the “... spirally arranged leaf-like structures”… DELAVORYAS (1962, p.120) commented that “...at Medullosa...leaves in their­basal­region­resemble­stems­with­many­steles.­Exter- nally, it would be impossible to distinguish between leaf and branch.­Here­the­terms­stem,­leaf­and­stalk­are­usеd. 2.1. roots There is no published information on them, but it is possible that the stem, which is partly covered by wet sediments, also possesses the function of a root. The trichomes on the stem at­the­apex­of­the­plant­(CORSIN,­1932,­Fig.­29)­might­be­ root appendices. 2.2. the stem It is straight or slightly sinuous and covered by longitudinal striations and regular short transverse bars. A group of plants, regarded­by­DANZE-CORSIN­(1953)­as­alinae, do not have transverse­bars­and­BOERSMA­(1972)­excludes­them­from­ Mariopteris. There are few illustrations of stems. The stem is slightly elliptical with the leaf stalks, or their marks, situated at equal distances on the stem. One pair of leaves is located on the lower­external­part­and­another­pair­is­approximately­half­ the­distance­to­the­top­STUR­(1885,­pl.­22,­fig.­1).­STUR­ (1885,­p.­285,­pl.­22,­fig.­1)­regards­this­arrangement­as­a­ spiral­of­four­bases­in­one­cycle.­DANZE-CORSIN­(1953,­ figs.­7–9)­supposed­there­to­be­a­helix­built­of­five­leaves.­ ZEILLER (1888) regards the arrangement of the leaves as two generatrice situated at an angle less than 180°. The lon- gitudinal­striation­of­the­stem,­illustrated­in­many­figures,­is­ straight and does not indicate any spiral growth. The posi- tion of each of the four consecutive leaves is repeated along the stem, and can be regarded as helical that is not the result of­axial­rotation.­Therefore,­the­fourfold­alternation­charac- terizes­the­leaf­arrangement­–­Fig.1. Geologia CroaticaGeologia Croatica geologia croatica 65/3 361–366 4 Figs. 2 tabs. Zagreb 2012 Structure, habitat and seed of Mariopteris ZEILLER  Yanaki Georgiev Tenchov Geological­Institute­of­the­Bulgarian­Academy­of­Sciences,­G.­Bonchev­Street­Block­24,­1113­Sofia,­ Bulgaria; (ytenchov@abv.bg) doi: 104154/gc.2012.25 geologia croatica 65/3Geologia Croatica 362 There is neither information nor data for the total length of the stem, although the length of one cycle of leaves in a well-developed­stem­is­280­mm­(STUR,­1885,­Pl.­22,­fig.1).­ The­known­maximum­width­for­a­stem­is­22­mm­with­a­ gradual reduction in each cycle of about 1 mm. If this reduc- tion­in­width­was­even,­the­length­would­be­about­21­x­280­ mm = 6.0 m or more. 2.3. stalks and leaves The leaves are pinnate with a massive, longitudinally striate naked stalk (petiole) up to 150 mm long and 7 mm wide at its base.­The­stalk­axes­are­directed­upwards­at­a­40°­angle­to­the­ stem­axis­(DANZE-CORSIN­1953,­figs.7–9).­The­stalk­bifur- cates­for­the­first­time­at­an­open­angle­in­two­parts­(rachises­ in many authors), which in their turn bifurcate up to 5 times. After the third bifurcation they are covered by pinnae (lam- ina). The leaf blade is parallel to the stem and to the ground. Its­axis­is­either­parallel­to,­or­at­some­angle,­to­the­stem­axis.­ The pinnae in the blade are in one plane that is parallel to the stem­axis­and­the­ground.­The­pinnules­length,­width­and­neu- ropteroid or pecopteroid base depends on the species. BOERS MA (1972, tables VII to XIV) gives data for the size of the leaf elements for 7 species. Table 1 summarizes some of the data. Pinnules near the top of the plant can have spine- like lobes or are totally formed as spines. In the mariopterids, two architectural types of leaf blades are known and designated as bipartite and quadripartite. DANZE-CORSIN­(1953,­p.­57–58,­p.­256)­indicated­that­ the fronds of Mariopteris have in its base and along its length quadripartite leaves but are bipartite in its sub-terminal part. The transformation to bipartite in quadripartite leaves is doc- umented­by­DANZE-CORSIN­(1953­pl.­40,­fig.1;­Pl­10,­fig.­ 1,­respectively­pl.­11,­fig.2).­This­can­be­regarded­as­accel- eration during the growth in the leaf architecture of a spe- cies. She (idem p. 58, plate 56) supposed that simple pinna were situated at the terminal part of the stem, but this is not evident­in­the­figures.­BOERSMA­(1972)­does­not­mention­ anything about simple pinna, although he accepts that the genus Mariopteris­consists­of­two­groups­of­species­–­one­ that has bipartite leaves and another that has quadripartite leaves.­The­bipartite­leaf­possesses­exterior­pinna­that­grad- ually diminish in length. The quadripartite leaf possesses a long pinna at the base of the tertiary rachis, followed by a pinna­of­calceolate­form.­For­this­reason­he­divides­the­mar- iopterids into two genera: Karinopteris BOERSMA for bi- partite fronds and Mariopteris (ZEILLER, BOERSMA emend.) for quadripartite fronds. BOERSMA (1972) does not comment on the opinion of DANZE-CORSIN that bi- partite leaves are situated at the top of plants with quadripar- tite leaves. However, he indicated as “aberrant forms” those specimens of Mariopteris (ZEILLER, BOERSMA emend.) that have bipartite leaves. M. nervosa KIDSTON (1925, pl. Figure 1: Interpretations of leaf position. table 1: Maximum known size of leaves of Mariopteris ZEILLER Species Length mm Width mm Data from: M. acuta >500 > 240 Boersma fig. 76 DANZE-CORSIN p. 83 M. beneckeii 750–800 >260 Huth fig 5 DANZE-CORSIN p. 104 M. bourosii ? ? only P4, P5 known M. carnosa >140 > 320 CORSIN pl. 68 M. daviesii ? ? only P3 known M. dernoncourtii 600 250 DANZE-CORSIN p. 94 M. grandepinaa >230 >260 HUTH fig. 1 M. hirsuta ? ? M. hirta 350 > 200 DANZE-CORSIN p. 149 M. lobatifolia >259 160 DANZE-CORSIN pl. 63, fig. 2 M. microsauveurii >180 >150 DANZE-CORSIN pl. 59, fig. 1 M. muricata >370 > 180 Huth fig 2 STUR 1877 M. nervosa >180 >360 BOERSMA text fig. 7 M. odontophylla 160–180 > 120 DANZE-CORSIN p. 137 M. opulenta 750 >440 pl. 68 fig.1 DANZE-CORSIN p. 175 M. pachyphylla 450–600 >200 pl.61, fig.1 DANZE-CORSIN p. 202 M. robusta ? ? M. Sauveurii >180 >160 DANZE-CORSIN figs. M. Soubeirianii >400 300 DANZE-CORSIN p. 213 yanaki georgiev tenchov: Structure, habitat and seed of Mariopteris ZEILLER Geologia Croatica 363 144,­fig.­4,­4a);­BOERSMA­specimens­of­M. sauveurii (his pl.­5,­fig.10)­and­of­M. muricata (his­pl.­21,­fig.­55)­should­ all be regarded as “minute fronds of Mariopteris”. This sug- gests­that­the­proposed­taxonomy­should­be­re-examined. Both­type­of­leaves­are­asymmetric,­as­is­well­expressed­ by­the­width­of­their­internal­and­external­parts.­The­asym- metry was the subject of attention by DANZE-CORSIN (1953)­in­almost­all­species­described­by­her. The leaves are large and require strong stalks to support them. The length of the leaves is longer than the length of the distance between the leaf stalks. The plane of the leaf blade most probably is parallel to the ground. In adult plants the­lower­pair­of­pinnules­is­about­7­cm­while­the­next­is­ about 9 cm above the ground. 2.4. Aphlebia DANZE-CORSIN­(1953,­fig.7,­p.­45)­accepts­as­Aphlebia some­small­excrescences­at­the­base­of­the­leaves.­It­is­not­ supported here. 2.5. Pinna, pinnules and venation The pinnae are lanceolate and slightly or more asymmetric elements formed on stalk branches. The width and the length (which­can­be­more­than­300­mm),­depend­on­the­species­ and on the position on the leaf. The pinnules are the small- est part of the leaf blade and their morphology depends on the species as detailed by BOERSMA (1972). They are at- tached by pecopteroid or sphenopteroid bases. The basal ba- siscopic and acroscopic pinnules in a pinna of ultimate order, have strongly developed outgrowths of their basal basiscopic lobes. In some cases, the terminal pinnules of a pinna, and part or all of the pinnules in lower situated pinna, are formed in spines, as­figured­by­HUTH­(1912,­VIII,­143,­fig.­1).­The­ pinnules have a midvein that arises obliquely from the stalk, curves and reaches at least halfway up the pinnules and sec- ondary vein branches that emerge alternately from the mid- vein­and­dichotomise­one­or­more­times,­ending­at­the­apex­ of the pinnules. Cuticle analysis by BARTHEL (1962) and KERP AND BARTHEL­(1993­–­but­not­pl.­5,­fig.­1–4!)­established­that­ stomata are closely spaced on the lower surface of the pin- nules but absent from the upper surface.. 2.6. bud (“bulbil”) HUTH (1912) used the term bulbil for round buds, up to 1.5 mm across, occurring on the stems of some species of Mar- iopteris.­CORSIN­(1932)­regarded­them­as­an­early­stage­of­ unopened­pinna.­Some­of­them­occur­in­the­axils­of­normal­ leaves­(HUTH­–­fig­5)­and­others­on­the­inter-leaf­space­of­ the­stem­(HUTH­fig.­3;­CORSIN­1932­pl.­76,­fig­1).­It­seems­ that they never occur on fully-formed leaves. The leaf grew by linear development (envelopment, opening) from a spiral. Some phases of this are illustrated by­CORSIN­(1932,­fig,­29­and­plate­76,­figs­1–5),­HUTH­ (1912,­VIII,­141­fig.­2),­CORSIN­(1932­text-fig­29,)­and­ GOTHAN­(1935­pl.­29,­fig.­4).They­are­summarized­here­in­ Figure­2.­At­an­early­phase­the­spiral­looks­like­a­bud.­The­ leaf­spirals­are­parallel­(twin­spiral)­and­visible­in­fig.­4­of­ HUTH. After some growth, the two parts separate and turn to­left­and­right­as­in­an­open­leaf.­А­phase­of­this­is­illus- trated­by­CORSIN­(1932­at­fig.29­and­plate­76). Figure 2: Phases of leaf development. 1/A– a bud in the base of stalk (HUTH, 1912, 141, fig. 5); 2/B– bud in the middle of a stalk(HUTH 141, fig. 3); 3/C– bud developed in a twin spiral (HUTH 141, fig. 4); 4/D– the top of the stem with numerous unopened leaves (CORSIN 1932 fig.29); 5/E– leaf in the open- ing of the spiral (HUTH 141, fig. 2). geologia croatica 65/3Geologia Croatica 364 2.7. the spines The spine-like form of the pinnules seems to be provoked by­heliotaxes,­when­a­young­specimen­is­in­full­shadow­bel- low adult plants. In such cases, the leaves of its top part are directed upwards towards the light. They are covered by spine-like pinnules as documented in HUTH (1912, VIII 143,­Fig.1).­The­spines­help­the­enveloped­leaves­behind­the­ plant top to intertwine through the leaves of the adult spe- cies, (that shade out the light), and then to continue develop- ment over the other leaf. This is shown by M. carnosa (COR- SIN,­1932,­Pl.­68).­The­older­specimen­has­larger­pinnules­ and­no­spines­(left­part­of­the­figure).­The­younger­specimen­ (visible along x-y line), has smaller pinnules and numerous spines that are at y – the top of the specimen. When the plant reaches the sunny surface, the spine-like pinnules start to transform­themselves­from­their­base­towards­the­apex­as­ normal pinnules. Different phases of this transformation are illustrated­in­numerous­figures­of­CORSIN­(1932­–­pl.63,­ fig.­2,­pl.72,­figs.­2,­4),­DANZE-CORSIN­(1953)­and­in­that­ of HUTH (1912). Therefore, Mariopteris under some condi- tions can be intertwining with plants at an early phase of growth. 3. reProductIon Until now, it has generally been accepted that the mariopter- ids are pteridosperms, but there is a lack of evidence of their method­of­reproduction.­GOTHAN­(1935,­p.8–14)­supposed­ that vegetative reproduction was possible by means of buds. BOERSMA (1969) established that Mariopteris latifolia (BRONGNIART) ZEILLER is really a fern, and referred it to a new genus Fortopteris BOERSMA, as Fortopteris lati- folia (BRONGNIART) BOERSMA. It has quadripartite constructed leaves. This species (and genus) differs from the mariopterids by some denticulation of its pinnules, and by its stem having no transverse bars. The missing transverse bars on the stem stimulated DANZE-CORSIN to create a “group alineae” in the mariopterids. The possibility that Mariopteris is a seed fern is based on an analogy with Dicksonites pluckenetyii which has small seeds situated on the lower surface of its pinna. In Mariopt- eris the majority of fossils show the upper surface. This sug- gested­re-examination­of­slabs­with­Mariopteris in the Do- brudzha collection. A seed-bearing Mariopteris beneckeii (sample­N­16344)­was­found­on­a­sample­from­borehole­ number 218 at 1406 m depth, corresponding to a level about 218­m­above­the­base­of­the­Mogilishte­Formation­in­the­ middle­part­of­the­Langsettian.­The­specimen­shown­on­Fig. 3­is­from­a­young­leaf­in­which­a­part­is­reversed,­exposing­ its lower surface possessing at least one small seed. This sug- gests that Mariopteris as many other ancient plants e.g. some lepidodendrons, after some time in a vegetative phase en- tered a reproductive phase that then led to the death of the plant. Two advantages of this strategy are that the seed is dispersed far from the mother plant root (6 m. or more) and may be out of the Mariopteris carpet thereby enlarging its range, and secondly in opening up places in the habitat for a new generation of plants. In the one metre interval at 1406 m depth in borehole 218, there are seven samples of Mariopteris and another two with Eusphenopteris. Individual pieces of shale are about 1 cm­thick­and­the­unexposed­parts­of­them­also­contain­plant­ remains. The plants were preserved with their upper surface upwards,­either­by­being­flattened­by­an­inrush­of­turbid­ flood­water,­or­death­after­a­reproduction­phase.­Leaves­re- versed with their lower surface upwards are rarely found and illustrated. This seems to indicate that mariopterids lived in places with a low water dynamic. 4. Mariopteris constructIon Parts of the published accounts of several species are used for the construction of the Mariopteris plant. Those stems possessing the marks of leaf bases show them to be equally spaced with the distances between them being no more than 170­mm.­The­leaves­are­flat­and­directed­at­angle­to­the­stem­ direction. The construction of the fronds is regarded as phases in architecture building with the steps as: appearance –­acceleration­–­retardation­–­disappearance­–­Figure­4. 5. HAbItAt The habitat of the mariopterids has been rather poorly dis- cussed­in­the­past,­although­the­opinion­by­GOTHAN­(1913­ p.88) that Mariopteris­lived­on­the­forest­floor­as­a­creeping,­ climbing and intertwining plant is generally accepted. Un- fortunately, there is no real evidence to support this view. KERP­&­BARTHEL­(1993­plate­5,­figures­1–4)­accept­that­ the documented hooks are of a climbing Karinopteris, but the plant seams to be Eusphenopteris So, a climbing habit of Mariopteris is not supported by the facts. In­the­Dobrudzha­Coalfield,­Mariopteris specimens oc- cur in all coal bearing lithostratigraphic units. They are rare in­the­Rakovski­Formation­(Namurian­A),­frequent­in­the­ Mogilishte,­Makedonka­and­Krupen­Formations­(Namurian­ Figure 3. The seed-bearing specimen 16344 Dobrudzha Coalfield borehole 214, 1508 m in the Mogilishte Formation in the mid part of the Langsettian. I think this image would benefit from annotation eg an arrow pointing to the seed? yanaki georgiev tenchov: Structure, habitat and seed of Mariopteris ZEILLER Geologia Croatica 365 C­–Westphalian­D),­and­rare­upwards­ to­ the­Stephanian­ (Gurkovo­Formation).­They­are­also­rare­in­the­fluvial­sedi- ments where allochthonous fragments are rarely observed. As autochthonous specimens they are frequent in the sedi- ments overlying the coal seams, especially in the upper part of­the­Mogilishte­Formation. In­the­flood­plains,­the­Mariopterids­formed­a­thick­car- pet of creeping and intertwining Mariopteris plants. Here and there, some bush-like plants of Sphenophyllum and some seed ferns such as Neuralethopteris, Alethopteris, Lonchop- teris and Eusphenopteris – Table 2 occurred. Paripterids are allochthonous. The detached seeds are autochthonous and did not germinate in the full shadow and cold milieu bellow the Mariopteris carpet. During­flooding,­the­creeping­plants­were­submerged­in­ muddy­water­and­fine­sediment­may­have­been­deposited­on­ them..­This­could­explain­why­Mariopteris has no stomata on­the­upper­surface,­as­they­would­have­been­filled­by­the­ fine­sediment.­The­stalk­was­massive­enough­to­support­the­ large­leaf­and­the­fine­sediment­covering­it­after­the­retreat­ of­the­flood­water.­Sediment­could­be­washed­away­by­rain- fall, but if it dried the plant might die. In cases when the floods­covered­the­plain­to­significant­depth,­the­amount­of­ the­fine­sedimentary­deposit­could­be­so­thick­and­heavy,­ that the Mariopteris plants were crushed below it. This is the most probable reason why the leaves are mainly preserved with their smooth upper surface uppermost. The reproduction problem could also be bound up with floods.­The­area­of­a­flood­plain­that­is­covered­by­deep­wa- ter looses all its Mariopteris carpet, but the carpet seems to be­restored­very­rapidly,­post­flooding.­Ferns,­of­course,­can­ quickly­re-establish­from­dispersed­spores.­For­Mariopteris there are two possibilities that are at present hypothetical. The plants may quickly spread from areas beyond the reach of­the­flood­waters­or­be­re-established­by­seeds. 6. strAtIgrAPHIc dIstrIbutIon In euroPe The genus is known from the Namurian A to the Can- tabrian and the stratigraphic distribution in Europe is con- sidered by HUTH (1912). M. acuta, M. beneckeii, M. muri- cata and M. carnosa are found in the Donets Basin (NOVIK, 1952) and the North Caucasus (ANISIMOVA, 1979: NO- VIK, 1978). The species diversity in the Dobrudzha Coal- field­is­comparable­with­that­of­other­basins­around­the­Var- iscan ranges in Europe. 7. conclusIon Mariopteris plants formed a cover in the coastal and alluvial plains and around the swamps. This, combined with their creeping­growth­form,­explains­why­they­are­so­widely­dis- table 2: Mariopteris and associated plants in flood plain of the Svoge and Dobrudzha Coalfields Svoge Coalfield Dobrudzha Coalfield Mariopteris Associated Mariopteris Associated Westphalian D-Cantabrian absent robusta, sarana Sphenophyllum, Alethopteris, Callipteridium Westphalian C absent sarana Sphenophyllum, Alethopteris Westphalian B nervosa Sphenophyllum muricata, nervosa, Sphenophyllum, Alethopteris, Lonchopteris Westphalian A acuta, muricata Sphenophyllum, Neuralethopteris muricata, nervosa, Sphenophyllum, Alethopteris, Lonchopteris, Neuralethopteris Namurian C acuta, muricata Sphenophyllum, Neuralethopteris acuta, muricata, beneckeii Sphenophyllum, Alethopteris, Lonchopteris, Neuralethopteris Namurian A absent acuta Sphenophyllum, Alethopteris, Neuralethopteris Figure 4. Phases in architecture building. geologia croatica 65/3Geologia Croatica 366 tributed in the Variscan foreland of Europe. Their creeping habit helped them to cover the plains and to migrate along river­beds­and­ the­flood­ terraces.­Even­ if­ they­advanced­ yearly­by­only­1­metre,­in­the­2–3­Million­years­(life­span­ of M. acute and of M. medicate)­they­could­migrate­2–3.000­ kilometres along river banks, the coastal margin of the sea, the outer fringes of large lakes and through the swamps from the British isles to the Turkish Black sea coast and the Cau- casus. The climatic changes towards drier conditions and longer periods without rainfall would have reduced their habitat until they disappeared around the beginning of the Stephanian. AcKnowledgement This paper was presented at the Zagreb meeting 2011 and is a contribution to IGCP Project 575 “Pennsylvanian terres- trial habitats and biotas of southeastern Euramerica”. I am grateful to the reviewers for their remarks and help with lan- guage editing. reFerences ANISIMOVA,­O.I.­(1979):­Flora­i­fitostratigrafia­srednego­karbona­Sev- ernogo. 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STUR,­D.­(1885):­Die­Carbonflora­der­Schatzlarer­Schichten.­Abt.­I:­Die­ Farne­der­Carbonflora­der­Schatzlarer­Schichten.–­Beitr.­Kennt.­ Flora­Vorvelt,­Keiser.­Koenigl.­Geol.­Reichsanstalt,­11/1,­418­p. ZEILLER,­R.­(1878):­Vegetaux­fossiles­du­terrain­Houiller­de­la­France.­ Atlas. ZEILLER,­R.­(1879):­Vegetaux­fossiles­du­terrain­Houiller­de­la­France.­ –­Explic.­Carte­geol.­France,­4/2,­185­p. ZEILLER,­R.­(1888):­Vegetaux­fossiles­du­bassin­houiller­de­Valen- siennes.–­Etude­des­gites­minereauxde­la­France,­731­p. Manuscript received January 11, 2012 Revised manuscript accepted October 17, 2012 Available online October 30, 2012