The conifer Glenrosa falcata sp. nov. from the Lower Cretaceous of Spain and its palaeoecology

Review of Palaeobotany and Palynology 172 (2012) 21–32

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The conifer Glenrosa falcata sp. nov. from the Lower Cretaceous of Spainand its palaeoecology

Bernard Gomez a,⁎, Timothy A.M. Ewin b, Véronique Daviero-Gomez a

a CNRS-UMR 5276 Terre, Planètes, Environnement, Université Lyon 1, bât. Géode, 43 Bd du 11 Novembre 1918, 69622 Villeurbanne, Franceb Department of Palaeontology, The Natural History Museum, Cromwell Road, South Kensington, London, SW7 5BD, United Kingdom

⁎ Corresponding author.E-mail addresses: [email protected] (B.

(T.A.M. Ewin), [email protected] (V. Dav

0034-6667/$ – see front matter © 2012 Elsevier B.V. Alldoi:10.1016/j.revpalbo.2012.01.009

a b s t r a c t
a r t i c l e i n f o
Article history:Received 3 October 2011Received in revised form 21 January 2012Accepted 24 January 2012Available online 31 January 2012

Keywords:conifersGlenrosastomatal cryptspalaeoecologyEarly CretaceousSpain

Based on short shoots and isolated leaves collected from the upper Barremian coaly clays of the La HuérguinaFormation (Uña–Las Hoyas basin, Iberian Ranges, Spain) a new species of the fossil conifer genus GlenrosaWatson et Fisher emend. Srinivasan is here described for the first time in Europe. Glenrosa falcata sp. nov. dis-plays the characteristic stomatal crypts and papillae projecting into the crypt neck, however it is differentiat-ed from other Glenrosa species by its falcate leaf morphology with a long free part (over 50% of the leaflength), an acute and recurved leaf tip and robust epidermal cell papillae. Based on comparisons with livingangiosperms possessing stomatal crypts (Nerium Linnaeus (Apocynaceae) and Blossfeldia Werdermann(Cactaceae)) and an assessment of the palaeoenvironment we conclude that G. falcata was a xerophytic shrub,that grew onwell drained substrates in a seasonally dry and warm climate and formed a minor part of a vegeta-tion dominated by the Cheirolepid Frenelopsis (Schenk) emend. Watson. This habitat was alkaline andoligohaline and therefore expands the previously reported environmental tolerances of Glenrosa.

© 2012 Elsevier B.V. All rights reserved.

1. Introduction

Fossil conifer foliage is frequently found disarticulated, due totransport and preservation processes. This, along with the frequentclose similarities in gross shoot morphology between many unrelatedfossil conifer taxa, in particular scale-like leaves arranged spirally orin opposition along an axis, has resulted in palaeobotanists develop-ing a taxonomy based on leaf cuticular features, especially the struc-ture of the stomatal apparatus (Harris, 1979).

In recognition of this, the genusGlenrosawas erected byWatson andFisher (1984) to include two species of fossil conifer leaves with a grossmorphology similar to Brachyphyllum Brongniart emend. Harris orPagiophyllum Heer emend. Harris but which display ‘communal stoma-tal pit’ (herein referred to as stomatal crypts); a unique characterwithingymnosperms. These stomatal crypts contain several stomata groupedat the bottom of a large, ampulla-shaped pit that is sunken into theme-sophyll, covered by cuticle and displaying numerous interdigitating,finger-like processes projecting into the crypt neck. The epidermis ofGlenrosa can therefore be differentiated from other scale-leaved coni-fers as they lack stomata on the exposed leaf surface between crypts.Srinivasan (1992) described a further two new species from themiddleAlbian of the Potomac Group at Puddledock, Virginia, USA and alsoemended the description to include reproductive organs.More recently,

Gomez), [email protected]).

rights reserved.

Zhou et al. (2000) described a fifth species from the Lower Cretaceous(Albian?) of Nanjing, Eastern China. Gomez et al. (2001) mentionedthe presence of a new species of Glenrosa from the Barremian of Spainbut did not officially describe it. It is the full description of this materialwhich forms part of this paper.

The affinities of Glenrosa remain unresolved. Watson and Fisher(1984) initially suggested the genus was part of the Cheirolepidiaceaeon the basis that the fossils were found in association with othergenera firmly assigned to this family and that the cuticle was thick,possessed characters such as papillae around the crypt margin andwithin the neck of the stomatal crypt which are similar to papillatestomatal pits seen in other Cheirolepidiaceae genera. However,based on the morphology of reproductive organs and attached pollenSrinivasan (1992) suggested that they displayed a closer resemblanceto the Cupressaceae (including Taxodiaceae) although she did notrule out a relationship with the Cheirolepidiaceae.

It has been noted by all the authors of the various Glenrosa speciesthat they are frequently found in association with other xerophyticconifers, particularly Frenelopsis (Schenk) emend. Watson and Pseudo-frenelopsis Nathorst emend. Watson, of the Cheirolepidiaceae. Watsonand Fisher (1984) pointed out that Glenrosa texensis (Fontaine)Watsonet Fisher (the type-species) and Glenrosa pagiophylloides (Fontaine)Watson et Fisher were found in association with Pseudofrenelopsisparceramosa (Fontaine) Watson from the Barremian–Aptian of Trent'sReach (Virginia, USA); and Frenelopsis alata (K. Feistmantel) Knoblochand P. varians (Fontaine) Watson from the upper Aptian–lowest Albianlimestones of Glen Rose (Texas, USA) respectively. Srinivasan (1992)

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22 B. Gomez et al. / Review of Palaeobotany and Palynology 172 (2012) 21–32

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observed thatGlenrosa hopewellensis Srinivasan andGlenrosa virginiensisSrinivasan, from the middle Albian of the Potomac Group at Puddledock(Virginia, USA) occurred with Frenelopsis (Schenk) emend. Watson andPseudofrenelopsis Nathorst emend. Watson co-occurred in the samebeds. Zhou et al. (2000) described Glenrosa nanjingensis from theLower Cretaceous (Albian?) of Nanjing (Eastern China) and also ob-served that Suturovagina intermedia Chow et Tsao (= Pseudofrenelopsisintermedia according to Watson, 1988) and Classopollis-bearing malecones of Classostrobus cathayanus Zhou co-occurred. The occurrence ofFrenelopsis and Pseudofrenelopsis species, with their scale leaves, fleshy‘succulent’ stems, thick cuticles and stomata sunken in pits surroundedby papillae, in addition to the unique cuticle characteristics of Glenrosahas unsurprisingly, led to the suggestion that they are xerophytic andinhabited a marine or haline influenced terrestrial environment.

Stomatal crypts are almost unknown in gymnosperms (extant orfossil) outside of Glenrosa. The only other conifer species to displaystomatal crypts is Sedites rabenhorstii Geinitz from the upper Turonianof the Bohemian Cretaceous Basin of East Germany (Kunzmann,2010). Kunzmann (2010) noted the similarities between Glenrosa andthe type specimen of Sedites; however he retained a separation basedon the observation that the leaves were born in opposite and decussatepairs. Outside of the Gymnosperms, stomatal crypts are only observedwithin the eudicot generaNerium Linnaeus (Apocynaceae) and Blossfel-diaWerdermann (Cactaceae). The eudicot genera with stomatal cryptsare regarded as xerophytes and the organisation of groups of stoma-ta into crypts is a xerophytic adaptation (Coste and Flahault, 1990;Barthlott and Poremski, 1996).

This paper describes a new species of the genus Glenrosa; Glenrosafalcata sp. nov., from the Barremian of Spain, which constitutes thefirst report of the genus in the Cretaceous of Europe. The paper alsoassesses the types of environments Glenrosa inhabited and its envi-ronmental tolerances.

2. Geological and palaeontological setting

The specimens here described were collected from the upper Bar-remian coaly clays of the La Huérguina Formation near Uña, south-western Iberian Ranges, Cuenca, Spain (Gomez et al., 2001, 2002).The geology of the La Huérguina Formation and related El ColladoFormation exposed at Uña have been the subject of much detailed re-search by Gierlowski-Kordesch et al. (1991), Fregenal-Martínez andMeléndez (1994), Gomez et al. (2001) and Buscalioni and Fregenal-Martínez (2010). The La Huérguina Formation and El Collado Forma-tion form part of 5000 m of sediments laid down during the Upper Ju-rassic to Lower Cretaceous in the Iberian Ranges intracontinentalbasin of the Iberian Plate. No direct marine influence has been ob-served in these rocks at this time (Poyato-Ariza, 1997). The La Huér-guina Formation comprises a series of lacustrine, and palustrinelimestones and marls that are the lateral equivalents of and whichinterdigitate with, the alluvial clays and sandstones of the El ColladoFormation. These sedimentary rocks were deposited in a series ofbasins formed by listric faulting and bounded by Middle Jurassic lime-stone massifs.

The environment of the upper Barremian of the Iberian Ranges isconsidered to be seasonal subtropical with alternating wet and dryseasons (Buscalioni and Fregenal-Martínez, 2010). A palaeogeogra-phical and palaeoclimatic reconstruction by Ziegler et al. (1983)placed this area at the dry divergent subtropical zone at a latitudeof 25–30°N and suggested that there was seasonal aridity basedon analysis of fossil plants. Climate models for the Barremian also

Plate I.Macromorphology and light microscopy of Glenrosa falcata Gomez, Ewin et Daviero-GLeafy axes bearing from two to nine leaves still in connection (×8.7; UÑ15–20). The holotypthe leaf. 2, entire leaf, (×38; UÑ22); 3, part of abaxial cuticle with oval crypt (×61; UÑ21). 4–UÑ21); 5, oval stomatal crypt (×460; UÑ22); 6, oval stomatal crypt (×400; UÑ23). 7, Two fi

of papillae showing a conical shape (×380; UÑ21). 9, External view of the cuticle surface w

suggest seasonality and high evaporation rates are thought to be themain driver of aridity during the dry season (rather than low precip-itation) (Haywood et al., 2004). Facies analysis of various parts of theUña and adjacent basins consistently suggests seasonality in wateravailability including lacustrine non-glacial varves (Gómez-Fernándezand Meléndez-Hevia, 1991) and charcoal in flash-flood and palustrinedeposits (Buscalioni and Fregenal-Martínez, 2010).

At Uña, the La Huérguina Formation is composed of 53 m of fluvi-al, lacustrine and palustrine limestones and marls that are interdigi-tated with a single set of alluvial sands and clays of the El ColladoFormation (Gomez et al., 2001). These rocks represent a regressive–transgressive cycle in the marginal zone of a small alkaline lake(Gomez et al., 2001). These and co-occurring sedimentary rocks in theadjacent La Huérguina basin contain abundant fossils including ostra-cods (Brenner, 1976), molluscs (Gierlowski-Kordesch and Janofske,1989), insects and vertebrates including fish, chelonians, lizards, asnake, crocodiles, dinosaurs and mammals (Krebs, 1995). The vegeta-tion grew in profusion in this wetland environment andwas dominatedby algae and aquatic plants (Martín-Closas, 2005). These include blue-green algae (Gierlowski-Kordesch and Janofske, 1989), charophytes(Brenner, 1976; Schudack, 1989; Martín-Closas and Diéguez, 1998),sporomorphs (Menéndez-Amor, 1970; Mohr, 1987, 1989), pterido-phytes (Sanz et al., 1988), conifers (Gomez et al., 2001, 2002) andearly aquatic angiosperms (Daviero-Gomez et al., 2006).

The dispersed leaves and shoots of Glenrosa, along with Frenelopsisremains, were collected from crevasse-splay lobes (Uña 3 or 4 ofGomez et al., 2001) that formed within the palustrine sediments ofthe flood plain in close proximity to the lake at Uña. The plantswere deposited under permanent water during a flooding event andwere preserved due to their rapid burial (Gomez et al., 2001). However,the fragmentary remains of both Glenrosa and Frenelopsis at this site aswell as that they were preserved in alluvial sedimentary rocksled Gomez et al. (2001) to suggest that they were not growing closeto the lake shore but were transported from the upper deltaic plain(see fig. 7 in Gomez et al., 2001). The soils of the upper deltaic plainare also presumed to have been basic oligohaline and experienced sea-sonal aridity based on environmental proxies within the El ColladoFormation and that thewhole areawas underlain by a karstic limestonebasement (see fig. 4 for palaeogeographical reconstruction in Gomez etal., 2001).

Thus, Glenrosa falcata inhabited the upper deltaic plain along withFrenelopsis, close to a permanent lake and wetland area which expe-rienced a continental, subtropical climate with hot dry and coolerwet seasons. These plants did not inhabit the wetland areas close tothe lake but were washed into the area during a wet episode orflood from the upper deltaic plain.

3. Material and methods

The descriptive part of this study is based on six leafy shoots andsixty eight isolated leaves that were obtained by bulk maceration ofthe sediment (coal-bearing lutites, dark grey in colour and laminatedin places) in hydrochloric acid (HCl, 10 N), followed by washing withwater in a fine mesh sieve (0.5 mm) and sorting under a stereomicro-scope. These fossil plant cuticles were further macerated in Schulze'ssolution reagent for a time, depending on the degree of carbonisationand preservation. The cuticles were then rinsed with water, neutra-lised in a diluted solution of ammonia (3%) and remaining siliceousremnants removed using hydrofluoric acid (HF, 40%). Cuticles wereprepared for light microscopy by separating the abaxial and adaxial

omez sp. nov. from the Lower Cretaceous (upper Barremian) of Uña (Cuenca, Spain). 1,e is specimen UÑ18 in 1d. 2–3, Shape, position and orientation of the stomatal crypts on6, Stomatal crypt showing different levels of papillae. 4, rounded stomatal crypt (×420;rst external levels of papillae closing the stomatal crypt (×450; UÑ21). 8, Internal levelith short, blunt papillae (×280; UÑ21).



cuticle surfaces with two fine needles and then staining them withsafranine before mounting on glass slides in glycerine jelly. Thesewere examined under a Leitz Aristoplan light microscope (LM), andphotomicrographs were taken with a Wild Photoautomat MPS45–51S at the Université Lyon 1 (Claude Bernard) and CNRS UMR5276 (Villeurbanne, France). Some cuticles were mounted on stubsfor scanning electron microscopy, coated with 100% gold and exam-ined using a Hitachi S800 SEM instrument in the Centre de Micro-structructures (CTμ) of the Université Lyon 1 (Claude Bernard ).Finally, other entire specimens were treated according to the oneweek technique of Bernard Lugardon, with the prepared moulds sec-tioned to a thickness of 1 μm, using a Reichert ultracutS microtome.The sections were mounted on glass slides and coloured with a metal-lic blue stain and examined using the aforementioned lightmicroscope.

4. Systematic palaeontology

Order CONIFERALESFamily INCERTAE SEDISGenus Glenrosa Watson and Fisher, 1984 emend. Srinivasan, 1992Type: Glenrosa texensis (Fontaine, 1893) Watson and Fisher, 1984.

Glenrosa falcata Gomez, Ewin et Daviero-Gomez sp. nov.Plates I–IV, Fig. 1, Table 1

Etymology: From the falcate shape of the leaves which resemble hornsor hooks.

Holotype: UÑ18. Here designated. Plate I, 1d.

Paratypes: UÑ36–37. Here designated. Plate III, 1–8 and Plate IV, 1–8.

Material: Six short, unbranched leafy shoots and sixty eight isolatedleaves. Specimen numbers UÑ15–37 of the Museo de Cuenca, Cuenca,Spain.

Type locality: Uña fossil site, Serranía de Cuenca, Cuenca, Spain.

Type horizon: Coaly clays 27 m above the base of the section at Uña(Uña 3–4 fig. 2 in Gomez et al., 2001), upper Barremian, LowerCretaceous.

Diagnosis: Shoots bearing helically arranged leaves. Leaves, c.1.0–3.0 mm long, thick, falcate with the lower part of leaf short andadpressed with the free part long, exceeding half of total length andspreading. Leaves keeled with a broad rhomboidal cushion. Leafapex acute and pointed, leaf margins converging between 10 and20°. Leaves amphistomatic with stomatal crypts randomly scatteredover whole leaf. Leaf cuticle thick and robust with a rugged externalsurface displaying short, blunt papilla over each epidermal cell onboth surfaces. Stomatal crypts number 5–10 per leaf and mostly ellip-soidal and longitudinal in cross-section with (usually) an ovalaperture. Crypt walls formed by both epidermal and subsidiary cells.Usually 2 to 8 stomata tightly packed together at the base of thecrypts which frequently share subsidiary cells. Subsidiary cells usuallynumber 4–6 per stoma and usually display polar subsidiary cells.Crypt neck partially occluded by long, interdigitating, finger-likeprocesses that arise from both the subsidiary and epidermal cells.Description: External morphology. The shoots are well preserved butare only known from six short lengths of unbranched axes (Plate I,

Plate II. Light microscopy of Glenrosa falcata Gomez, Ewin et Daviero-Gomez sp. nov. from thsections of a stomatal crypt (×780; UÑ24–35).

1). The longest shoot (UÑ20 Plate I, 1f) is 3.5 mm long and consistsof just nine leaves. Although the specimen UÑ18 (Plate I, 1d) consistsof only two leaves attached, it has been chosen as the holotype be-cause it bears the longest leaves. The shoot width varies from 1.5 to2.0 mm. The leaves are inserted as a simple helix in 1+3 phyllotaxisand diverge from the axis at an angle of between 30 and 45°. The leafsize varies from 1 mm to 3 mm long (free part+basal cushion) and isfrom 0.7 mm to 1.5 mm wide at the base. The leaves are generallyhorn to hook-shaped that frequently have an incurved tip (Plate I,1a–f). This gives the leaves an ‘S’ shaped outline. The abaxial surfaceis thus concaved towards the base but medially convex. The free ad-axial surface is 1.0–2.5 mm long, always exceeds half the total leaflength and may be as much as 90%. The leaf apex is usually an acutepoint with the lateral margins forming a narrow angle of 10–20° al-though may be rounded in rare cases. The leaf surface is uniformlyfinely rugged. The leaf margins are sharp and entire.

Cuticle structure. The cuticle compressions are exquisitelypreserved and thick; 3–10 μm (c.a. 5 μm), providing the leaves witha very tough appearance. The abaxial and adaxial cuticles display sim-ilar thicknesses. The leaf is amphistomatic with stomatal cryptssparsely and irregularly distributed across the leaf (Plate I, 2–3;Plate III, 1–2). There are 5–10 stomatal crypts per abaxial leaf surfacewith fewer on the smaller adaxial cuticle. The crypts are clearly sepa-rated from each other and predominantly oriented longitudinally fol-lowing the leaf margins. The stomatal crypts are ellipsoidal, oval or(rarely) globular (Plate I, 4–8; Plate IV, 7) and measure 70–190 μmlong (c.a. 130 μm) and 40–100 μm wide (c.a. 65 μm). Crypt aperturesare rounded to ellipsoidal (Plate I, 4–6) and surrounded by long papil-lae that arise from epidermal cells around the aperture and thoseforming the walls of the pit neck. These papillae are significantly lon-ger and more pointed than the epidermal papillae and interdigitatewith one another to constrict/occlude the crypt mouth (Plate I, 4–8;Plate III, 1; Plate IV, 1–3). Lower down inside the crypts tiers of longer,sometimes bifurcate, finger-like projections arise from the bottomand project towards the pit aperture (Plate II, 1–12). The basal papil-lae (Plate IV, 8) are 8–13 μm long (c.a. 10 μm) and 7–17 μm wide (c.a.14 μm) and mostly display obtuse to rounded apices. Two to eightstomata are present in the crypt base (Plate III, 7–8). The stomataare elliptical and about 40–70 μm long (c.a. 55 μm) and 30–60 μmwide (c.a. 45 μm). There are 4–6 subsidiary cells per stoma (Plate IV,4–6) and these are often shared between adjacent stomata. Usually,two of them are polar with the others being lateral. The subsidiarycells are 24–37 μm long and 12–17 μm wide and are separated by1–3 μm thick anticlinal walls. A reconstruction of a stomatal crypt intransversal section has been drawn from seriate sections (Fig. 1).The ordinary epidermal cells of both surfaces are polygonal, rectangu-lar or more or less isodiametric or slightly elongate (Plate I, 3; Plate III,4) and measure 15–30 μm long and 7–19 μm wide. They are in partsarranged in faint and discontinuous longitudinal files or strips butappear randomly orientated in other areas. Each of them bears ashort, blunt papilla (Plate I, 9; Plate III, 1, 3). The anticlinal walls ofthe ordinary epidermal cells are straight and pitted and about 3–7 μmthick. Those of the subsidiary cells and epidermal cells in the crypt arethinner and only measure 1–2 μm thick. Delicate hypodermis is presentin the inner side of both adaxial and abaxial cuticles and is more devel-oped in the non-stomatal areas of the crypt (Plate III, 2; Plate IV, 7). Thiscuticle consists of elongate cells, which are hard tomeasure because thetransversal anticlinal walls are frequently obscure.

Discussion and comparison: Only rare, fragmented specimens of Glen-rosa falcata are known. They have only enabled an estimation of thephyllotaxis while the branching pattern is unknown. The relatively

e Lower Cretaceous (upper Barremian) of Uña (Cuenca, Spain). 1–12, Seriate semi-thin


Fig. 1. Reconstruction of a stomatal crypt of Glenrosa falcata Gomez, Ewin et Daviero-Gomez sp. nov. from the Lower Cretaceous (upper Barremian) of Uña (Cuenca, Spain).


thick and fleshy shoots suggest the plant may have been succulent, ashas been implied for other Glenrosa species (Watson and Fisher,1984). The majority of the available leaves (both attached to shortshoot fragments and dispersed) share the horn or hook-shaped mor-phology with a recurved apex thus demonstrating that this is a con-sistent and taxonomically useful character that can be used todistinguish this species.

Amongst Glenrosa species (Table 1), Glenrosa texensis (Fontaine)Watson et Fisher and Glenrosa nanjingensis Zhou et al. are readilydifferentiated from Glenrosa falcata on leaf morphology as they areadpressed, scale-like with rounded obtuse apices that bear little re-semblance. Furthermore, G. nanjingensis is hypostomatic and G. texen-sis has a fimbriate margin. The leaves of G. falcata bear a closerresemblance to the spreading leaves of Glenrosa virginiensis Sriniva-san, Glenrosa hopewellensis Srinivasan and Glenrosa pagiophylloides(Fontaine) Watson et Fisher. However, the longer, straighter leafmorphology and the more rounded apices of the latter two immedi-ately differentiate them from the more falcate leaves with acuteapices of G. falcata. The leaves of G. virginiensis bear closest resem-blance to G. falcata however the two can be quickly differentiated inthat G. falcata displays significantly more robust and numerous epi-dermal cell papillae and has a longer free part of the adaxial leaf(i.e. is less adpressed). The helical arrangement of G. falcata leaveswas only roughly established and so comparisons based on phyllotax-is are not that meaningful (see Table 1).

With regard to the micromorphological characters the short bluntpapillae born by the ordinary epidermal cells of Glenrosa falcata are

Plate III. Scanning electron micrographs of Glenrosa falcata Gomez, Ewin et Daviero-Gomezternal view showing the stomatal crypts protected by triangular papillae, and the epidermalstomatal crypts, the epidermal cells being covered and masked by elongate hypodermal cellscells with narrow, rather deep grooves between the papillae (×70; UÑ37). 4, Isodiametricstrangled aperture in comparison with the size of the stomatal crypt (×640; UÑ36). 6, Latearound the aperture (×550; UÑ36). 7, Internal view showing a stomatal crypt with one stomcrypt with at least seven well distinguished stomata (×460; UÑ36).

particularly distinctive although are similar to those of Glenrosa pagio-phylloides. Epidermal papillae reported and depicted by Srinivasan(1992, Plate I, 1–3) for Glenrosa virginiensis are considerably smaller,less abundant and more connate than in G. falcata. The stomatalcrypts of the other six species appear to be similar in structure, butG. falcata shows more deeply sunken pits.

The suit of characters displayed by Glenrosa falcata is remarkablein that most are shared, in part, with other members of the genus.This is especially true for the falcate leaves which resemble those ofGlenrosa virginiensis and the rough epidermal cells bearing robustpapillae which resemble those of Glenrosa pagiophylloides. Watsonand Fisher (1984) considered that the difference in shoot morphologybetween the adpressed leaves of Glenrosa texensis and the spreadingleaves of G. pagiophylloidesmight represent differences in foliage ma-turity. Similarly therefore, the discovery of G. falcata seems to suggesta relationship between both G. virginiensis and G. pagiophylloides.However, as G. falcata is clearly distinct in hand specimen and micro-scopically from these species, separation is maintained, although itmay suggest a close relationship between these species.

The systematic position of Glenrosa remains unresolved. The ma-terial studied here does not contribute anything further to elucidatethe affinities of this genus although it is perhaps significant that thesharing of subsidiary cells is a character most commonly seen withinmodern Cupressaceae (Ewin, 2004).

The only other conifer to possess stomatal crypts is the Upper Cre-taceous species Sedites rabenhorstii (Geinitz) Kunzmann (Kunzmann,2010). This long forgotten species was differentiated from Glenrosa

sp. nov. from the Lower Cretaceous (upper Barremian) of Uña (Cuenca, Spain). 1, Ex-cells covered with short, blunt papillae (×180; UÑ37). 2, Internal view showing several(×90; UÑ37). 3, Short and blunt papillae borne by the periclinal walls of the epidermalepidermal cells without hypodermis (×140; UÑ37). 5, Elliptical stomatal crypt with aral view showing stomatal crypt with on the top the most external papillae arrangeda open and two closed (×550; UÑ36). 8, Internal view showing round to oval stomatal



based on the arrangement of the leaves in opposite and decussate pairs.In addition to the phyllotaxis S. rabenhorstii (Geinitz) Kunzmann canalso be differentiated from Glenrosa falcata as the leaf apicesare rounded (i.e. not acute), that the cuticle surface does not displayrobust papillae over the epidermal cells and that the stomatal cryptsare arranged in loose rows.

Outside of Glenrosa and Sedites the only other vaguely comparablefossil conifer genus to Glenrosa falcata is Tarphyderma Archangelskyand Taylor (1986, 1991). However this is readily distinguished asthe stomatal chambers are narrower, more elongate, are formed bytiers of vertically elongate subsidiary cells (rather than in combinationwith epidermal cells) and only contain a single stoma at the bottom ofthe chamber.

Watson and Fisher (1984) and Zhou et al. (2000) drew analogieswith the stomatal arrangement within the living angiosperms Neriumoleander L. and N. odorum Scland of the Apocynaceae (Metcalfe andChalk, 1950; Coste and Flahault, 1990). These extant species, however,differ significantly in that they have much bigger stomatal crypts,incorporating a larger number of specialised epidermal cells thatbear longer and more slender interdigitated hair-like processes. Fur-thermore, the stomata of the oleanders are un-crowded and rarelyshare subsidiary cells (Watson and Fisher, 1984). The extant dwarf,fleshy Cactaceae Blossfeldia liliputana Werdermann also display sto-matal crypts but differ from Glenrosa by possessing more stomatawithin the crypts that are larger and more spherical in shape andthat the covering hairs are significantly more sinuous and tangled(Barthlott and Poremski, 1996).

5. Palaeoecology and palaeoenvironment

5.1. Palaeosynecology

The typical association of Glenrosa with members of the Cheirole-pidiaceae, as described by Watson and Fisher (1984) and Zhou et al.(2000), is also seen in the Uña palaeoenvironment, where Glenrosafalcata is found in association with Frenelopsis ugnaensis Gomez andits related Classopollis-bearing microsporangiate cones Classostrobusugnaensis Gomez (Gomez et al., 2002). Zhou et al. (2000) suggestthat the Chinese Glenrosa may have been a shrub-like plant that grewwithin stands of Cheirolepidiaceae. Similarly, we suggest that G. falcatawas a shrub-like plant that grewwithin dense stands of the cheirolepidF. ugnaensis Gomez as this would account for the acute cuticular adap-tations to water loss and the low abundance of G. falcata within thisflora.

5.2. Palaeoenvironments

Watson and Fisher (1984) and Zhou et al. (2000) both suggestedthat Glenrosa inhabited hot and dry habitats with high rates of evap-oration. Sedimentological analysis indicates that the North AmericanGlenrosa species inhabited an environment that also experiencedstrong marine influences (Daghlian and Person, 1977; Upchurch andDoyle, 1981). These plant fossils were deposited in saline coastal la-goon or bay depositional systems suggesting that the plants were tol-erant of hyper-saline conditions or, at least, experienced them tosome extent. Despite the sediments being poorly known, Zhou et al.(2000) suggested that the Chinese species inhabited areas near tocontinental (inland) marshes and/or water bodies. The supposed

Plate IV. Scanning electron micrographs of Glenrosa falcata Gomez, Ewin et Daviero-GomeExternal view of the stomatal crypt closed by several levels of papillae surrounded by th(×550 μm). 4, Internal view of a stomatal apparatus with a papilla-shaped projection comincells (×730; UÑ36). 6, Stomatal apparatus with four subsidiary cells (×730; UÑ36). 7, Intebottom of an oval stomatal crypt, the epidermal cells that form the crypt near the aperturestomatal crypt (×640; UÑ37).

xerophytic adaptations of this species were cited as a response to ei-ther seasonal drought or the abundance of salt or alkalis due to highevaporation rates. An analysis of the sedimentary rocks and plant fos-sils at Uña demonstrates, for the first time, that Glenrosa could toler-ate both saline and alkaline rich environments and that Glenrosafalcata probably inhabited continental freshwater habitats betweenseasonally dried, braided channels that opened into a lake system(Gierlowski-Kordesch and Janofske, 1989; Gomez et al., 2002). ThusG. falcata inhabited an environment that was more similar to Glenrosananjingensis and thereby suggests that Glenrosa was not restricted tonear marine/halophytic environments.

5.3. Palaeoautecology

Leaf and cuticle morphology of conifers can be related to palaeo-climate (Thévenard et al., 2005). Under arid conditions, stomatal ap-paratuses are critical areas for water balance. To reduce transpirationduring such conditions plants display several specialised microstruc-tures. Most of these are thought to limit transpiration induced by dryair circulation over the leaf surface i.e. increase boundary layer resis-tance (Willmer and Fricker, 1996). The numerous morphological andmicrostructural features of Glenrosa (i.e. tiny leaves, thick cuticles,short blunt epidermal papillae, stomata confined at the bottom of sto-matal crypts, crypts filled with hair-like papillae borne by epidermalcells and well-developed hypodermis) have been reported to repre-sent extreme xeromorphic adaptations that probably assisted inavoiding excessive water loss (Watson and Fisher, 1984; Zhou et al.,2000). Thus, boundary layer resistance in Glenrosa is primarily in-creased by clustering the stomata together at the base of deep stoma-tal crypts which, is further enhanced by numerous interdigitatinghair-like papillae projecting into the crypt chamber, neck and aroundthe aperture. Transpiration may also have been reduced as thesepapillae may also have acted as points of condensation for moistureoccurring within the crypt. Similarly, the many micro grooves formedby the papillae and the boundaries between anticlinal cell walls thatform the crypt observed inside the stomatal crypts (Fig. 1) and therough cuticle surface seen in Glenrosa falcata and Glenrosa pagiophyl-loides amongst others could also have acted as areas in which waterwas trapped. This trapped or condensated water could have reducedwater stress, cooled the leaf and may have even reabsorbed whentemperatures drop (e.g. during day/night variations). Indeed, thestomata are so well protected in the crypts that there is no need forfurther adaptation at the level of the stomata, and there is correspond-ingly no differentiation of inner or outer papilla. As such, stomatalcrypts probably indicate high osmotic constraint in the palaeoenviron-ment of the upper Barremian of Uña.

Glenrosa pagiophylloides, G. virginiensis, G. hopewellensis, and G.falcata all display spreading amphistomatic leaves. As such, the po-tential photosynthetic and water loss surface area are increased,somewhat contradicting the xerophytic characteristics of thick leath-ery leaves and stomatal crypts. Particularly as adpressed scale leaveshave frequently been cited as a xerophytic adaptation. However,Glenrosa has frequently been suggested to be a small shrub thatgrew beneath and within stands of Frenelopsis and Pseudofrenelopsistrees (Zhou et al., 2000). Thus, the assumed reduction of transpirationcreated by the presence of stomatal crypts might counterbalance theincreased water loss caused by a more spreading habitat, therebymaximising CO2 take up and photosynthesis thereby improving the

z sp. nov. from the Lower Cretaceous (upper Barremian) of Uña (Cuenca, Spain). 1–2,e short, blunt papillae of the epidermal cells (×410; UÑ37). 3, Same as in A and Bg out between the guard cells (×690; UÑ37). 5, Stomatal apparatus with six subsidiaryrnal view showing folds of the hypodermis, and stomatal apparatuses located on thebeing evaginate (×230; UÑ36). 8, Evaginate epidermal cells near the aperture of the

Table 1Morphological and structural comparisons of Glenrosa species, including G. falcata. (1) Watson and Fisher (1984), (2) Srinivasan (1992), (3) Zhou et al. (2000), (*) type-species.

Characters/Glenrosa

G. falcata G. hopewellensis2 G. nanjingensis3 G. pagiophylloides1 G. texensis*,1,2 G. virginiensis2

Leafarrangement

Spiral Spiral Spiral Spiral Spiral Spiral

Phyllotaxy 1+3 – 8+13 – 1+2 –

Leaf shape Usually horn tohook-shaped

Falcate Scale-like,adpressed

Falcate,standing away at 80°

Scale-like,adpressed

Scale-like,adpressed basally

Leaf size 3 mm long1.5 mm wide

2–2.5 mm long,0.5–1 mm wide

2 mm long,1.5 mm wide

3 mm long,2 mm wide

3 mm long,2.5 mm wide

3–3.4 mm long1.6–1.8 mm wide

Free part >1/2 total length >1/2 total length Up to 1/5 tot. length About tot. length Up to 1/5 tot. length b1/2 total lengthLeaf apex Acute, sometimes

roundedBluntly rounded topointed

Obtuse or rounded Rounded Bluntly pointed Sub-acute to acute

Apical angle 10–20° in acutetips

? 90–120° ? up to 70° ?

Leaf margin Sharp, entire Mainly entire Somewhat fringed Sharp, entire Fimbriate hairsup to 65 μm long

Entire

Leaf epidermalsurface

Short bluntpapillae

Occasionally papillatealong margin

Smooth or rugged Short blunt papillae Undulate withoutpapillae

Irregularly spaced smallconical papillae

Cuticlethickness

3–(5)–10 μm Moderately thick Up to 10 μm Up to 10 μm Thick Rather thickand leathery

Cryptdistribution

Amphistomatic Amphistomatic Hypostomatic Amphistomatic Amphistomatic Amphistomatic

Abaxial cryptdistribution

Scattered Sparsely scattered Scattered Scattered Scattered Sparsely scattered

Adaxial cryptdistribution

Scattered Aligned along margin Absent Scattered Aligned along margin Sparsely scattered

Crypt density Up to 20 per mm²5–15 per leaf

10–12 per leaf Up to 7 per mm² Up to 8 per mm²

Size of abaxialchambers

70–190 μm long40–100 μm wide


100–120 μm long,65–75 μm wide

78 μm diameter 112 μm long,69 μm wide


Size of adaxialchambers

As for abaxialsurface

As for abaxial surface Absent As for abaxial surface 90 μm long, 66 μm wide Not differentfrom abaxial

Chamberapertureoutline

Oval tolongitudinal

Oval or circular Mostly ellipsoidaland longitudinal

Circular Oval Oval or circular

Stomata percrypt

2–8 1–6 2–3 2–4 4–8 2–6

Stomatal size 40–70 μm long30–60 μm wide


55 μm long38 μm wide

– 75 μm long50 μm wide


Inner and outerpapillae

More than 8 More than 9 More than 10 More than 8 More than 12 More than 12

Subsidiary cellsper stomata

4–6, often shared 4–5 6 (2 polar) ?, often shared 4–6, sometimes shared 4–5, occasionally shared

Hypodermisdevelopment

Well-developed ? Well-developed Weak-developed Well-developed ?

Occurrence Late BarremianSpain

Middle AlbianVirginia (USA)

Albian?East China

Late Aptian–Earliest AlbianTexas (USA)

Barremian–Mid AlbianVirginia (USA) and Texas (USA)

Middle AlbianVirginia (USA)


plants effectiveness especially if it were growing within a shaded and/or becalmed environment. Nevertheless, it remains unclear why Glen-rosa texensis had amphistomatic leaves and Glenrosa nanjingensishypostomatic leaves, despite both taxa displaying similar scale-likeand adpressed leaves growing in Cheirolepid dominated habitatsunless there were differences in the air turbulence and/or CO2

availability.The work of Haworth and McElwain (2008) also raises the possi-

bility that several aspects of the cuticle morphology of variousGlenrosa species served functions other than or in addition to xero-phytic roles. As such, the leathery leaves, rough cuticle surface and,in some species (G. pagiophylloides, G. virginiensis, G. falcata), epider-mal cell papillae may be indicative of adaptations against intense sun-light or, although less likely, poor nutrients. Furthermore, the papillaesurrounding and constricting the pit mouth may also have served toprevent excess water and possibly dust particles entering the stomatalcrypt in addition to increasing boundary layer resistance (Haworthand McElwain, 2008). Excess water in the crypt would be detrimentalas CO2 diffuses 10,000 times slower in water than in air (Brewer andSmith, 1995), whilst dust may resist stomatal pore closure and therebylead to excessive water loss. Similarly, the rounded epidermal papillaeof several Glenrosa species (G. pagiophylloides and G. falcata) look

reminiscent of those of Taxus baccata (Haworth and McElwain, 2008,fig. 2 a, b) and as such may also have assisted in the shedding of excesswater from the leaf during the wetter episodes which all the Glenrosaspecies probably experienced. That said however, it is felt that thecuticular features displayed by all Glenrosa species are predominantlyxerophytic adaptations butwhichwould have also served in other roles.

Nerium oleander L., cited for its similar stomatal crypts, inhabitsMediterranean regions (Raven et al., 1992) and naturally occurs onwell drained gravels in wadis and on river banks where water perma-nently flows, at least underground. Although this extant Apocynaceaelives in a warm and semi-arid climate the ground-water table isimportant (Nerium comes from the Greek “neros” meaning humid). Itis perhaps therefore more than coincidence that Glenrosa falcata shareda similar palaeoautecology in the upper Barremian of Uña, as it alsoinhabited a warm, semi-arid environment with dry and wet seasons,influencedby a high ground-water table and growing in close proximityto fluvial, palustrine and lacustrine systems (Gierlowski-Kordesch andJanofske, 1989; Fregenal-Martínez and Meléndez, 1994; Gomez et al.,2001). However, the extant dwarf fleshy Cactaceae Blossfeldia liliputanaWerdermann also displays stomatal crypts although this unusual plantgrows in fissures on rocky cliff faces at altitudes of between 700 and3400 m in Argentina and Bolivia. Blossfeldia is a poikilohydric plant


that can survive freezing during the winter by losing more than 80% ofits water (Barthlott and Poremski, 1996). However, stomatal crypts inBlossfeldia are more likely to be an adaptation to high temperaturesandwater deficiency experienced during the summer rather than a fea-ture to cope with freezing. The poikilohydric existence of B. liliputana isnot thought to be representative of Glenrosa; however the suggestionthat Glenrosa was succulent may be significant as stomatal crypts mayenable the plant to function more effectively when it is experiencingdrought.

Thus, the adaptive features in Glenrosa falcata are most probablyrelated to palaeoclimatic factors. Glenrosa falcata appears to beadapted to resist water loss during implied dry seasons that occurredin and around the lacustrine system at Uña during the Barremian.

6. Conclusions

The occurrence of Glenrosa falcata sp. nov. in the upper Barremianof the La Huérguina Fm. (South-western Iberian Ranges, Cuenca) rep-resents the first description of this characteristic genus in Europe.This occurrence thereby broadens the geographical distribution ofGlenrosa during the Lower Cretaceous from North America andChina/Asia into Europe. The presence of G. falcatawith the Cheirolepi-diaceae genera Frenelopsis and Pseudofrenelopsis also enlarges thisgeographic and stratigraphic co-occurrence, suggesting that theseplants were adapted to fill a similar environmental niche albeit withGlenrosa forming a minor part of this flora. The discovery that G.falcata inhabited an alkaline rich area also broadens the type of envi-ronments the genus could tolerate. Thus, Glenrosa appears to have oc-cupied a wide range of seasonally arid, fluvial to marine influencedenvironments during the late Early Cretaceous. This work, alongwith sedimentological information at other Glenrosa localities world-wide and comparison to modern analogies, suggests that Glenrosawas a shrub-like plant that grew within stands of Cheirolepidiaceaewhich inhabited well drained seasonally arid margins to fluvial chan-nels. Stomatal crypts prove not only to be of taxonomical value butalso of climatic significance although the xerophytic characters mayhave also served additional functions linked primarily to CO2 acquisi-tion and prevention of water logging.

Acknowledgements

Theauthors acknowledge Prof. Jane Franciswhohelped in improvingthe manuscript. B.G. and V.D.-G. received financial support from theCNRS-UMR 5276 Terre, Planètes, Environnement. This publication is acontribution to the projects ANR AMBRACE (No BLAN07-1-184190) ofthe French “Agence Nationale de la Recherché”, INSU NOVAMBRE 2,and projects CGL2008-00550/BTE, CGL2008-00809/BTE and CGL2009-11838/BTE funded by the “Ministerio de Ciencia e Innovación” of theSpanish government, and project SGR2009-1451 funded by the Catalangovernment. T.E. would like to thank J.V. Dallosso for proof reading andhelpful comments.

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The conifer Glenrosa falcata sp. nov. from the Lower Cretaceous of Spain and its palaeoecology