Cretaceous Research (2002) 23, 761–773doi:10.1006/cres.2002.1023

A new species of Mirovia (Coniferales,Miroviaceae) from the Lower Cretaceous of theIberian Ranges (Spain)

Bernard Gomez

School of Earth Sciences, University of Leeds, Leeds LS2 9JT, UK; e-mail: bernard@earth.leeds.ac.uk

Revised manuscript accepted 13 July 2002

The Lower–Middle Albian coaly clay bed of the Escucha Formation, which is exposed at Rubielos de Mora (eastern IberianRanges, Spain), contains a diverse fossil plant assemblage. Among the taxa present in this layer, Mirovia gothanii Gomez sp.nov. differs from other species of the genus by its greater leaf length, margins typically overhanging the depressed stomatalgroove, a single short, blunt, papilla borne by each subsidiary cell, non-stomatal cells inside the groove and margins, and ahigher number of resin ducts in the mesophyll. Morphological study of the well-preserved cuticles demonstrates that thespecies also occurs in Lower Cretaceous coals of Santa Maria de Meia (Pyrenees, Spain) where Gothan (1954) described itas Sciadopitytes sp. Both localities constitute the southernmost extent of the genus in Laurasia when the family was likely tohave reached its climax in terms of abundance and diversity. � 2003 Published by Elsevier Science Ltd.

K W: conifers; Mirovia; Early Cretaceous; Iberian Ranges; Spain.

1. Introduction

During the Early Cretaceous, all the modern coniferfamilies were represented in addition to a few extinctfamilies such as the Cheirolepidiaceae and theMiroviaceae. Living conifer leaves are typically in theform of needles or scales with one to two veins,although in some genera the leaves are wide andcontain many vascular bundles (e.g., Agathis). Harris(1969, 1979) classified Mesozoic conifer leaves ina system comprising eight form genera but furtherresearch, especially on specimens with preservedcuticle, has revealed a higher diversity of taxa (e.g., seeWatson, 1988; Watson & Alvin, 2000).

Aciculate fossil leaves displaying a median, abaxialstomatal zone or groove have for a long timebeen considered to be coniferalian, this characterbeing unique in modern needle-bearing conifers toSciadopitys verticillata (Thunberg) Siebold & Zuccarini(Manum et al., 2000). To name fossil Sciadopitys-likeleaves, Halle (1915), Florin (1922) and subsequentauthors used Sciadopitytes Goeppert & Menge. Thisgenus was, however, initially employed for leavespreserved in amber on the Samland Peninsula (BalticSea, along the coast of East Prussia, Russia) andsubsequently identified as members of the Ericaceae(Schimper & Schenk, 1890, pp. 346, 827). Morerecently Sciadopityoides Sveshnikova (1981) was

0195–6671/03/$30.00/0

substituted for Sciadopitytes Goeppert & Menge. Bose& Manum (1990) divided Sciadopityoides into fourgenera based on leaf and axis morphologies, leafstomatal distribution and other epidermal charactersof Barremian–Aptian specimens from Spitzbergen,Greenland and Baffin Island: Holkopitys Bose& Manum (monospecific), Mirovia Reymanownaemend. Bose & Manum (eight species), OswaldheeriaBose & Manum (four species) and SciadopityoidesSveshnikova emend. Bose & Manum (eight species).Additionally Bose & Manum (1991) attributed afifth genus, Tritaenia Maegdefrau & Rudolf (threespecies) to the extinct Miroviaceae Bose & Manum(1990, p. 64). All of these taxa have in common theabaxial, median stomatal zone, but this is set in awell-developed groove in Holkopitys, Mirovia andSciadopityoides, whereas is not protected in a groovein Oswaldheeria and Tritaenia. The taxonomy andsystematics of these genera and family have beenrecently discussed (Watson & Harrison, 1998;Manum et al., 2000; Watson et al., 2001).

2. Material

The well-preserved leaf cuticles described in thispaper were collected from a coaly clay layer withinthe Escucha Formation at the locality of El Paso,

� 2003 Published by Elsevier Science Ltd.

762 B. Gomez

A new species of Mirovia from Spain 763

near Rubielos de Mora (eastern Iberian Ranges,Spain). Gomez et al. (1999, 2000, 2002) havesystematically described the vegetative remains ofGinkgoales (Nehvizdya penalveri) and Cheirolepi-diaceae (Frenelopsis turolensis), and associated fertilemicrosporangiate cones (Classostrobus turolensis), andthe geological and palaeoenvironmental framework ofthis Early–Mid Albian assemblage.

3. Local palaeoenvironment

Sedimentological and taphonomic analyses haveshown that these species grew in a brackish coastalfloodplain of the huge Escucha Delta described byQuerol et al. (1992). Leaf-beds probably accumulatedin deltaic coastal marshes, which are low energyenvironments receiving a large amount of sediment.Their development involved a massive supply of entireleaf litter from the land around the marshes viahigh-energy fluvial transport during short, flood-ing events (Gomez et al., 2000). The presence ofmixed marine and freshwater algae, i.e. dinocysts andzygnematalean spores, respectively, confirms thatthese swamps received both marine and freshwaterinput. The xeromorphism of some taxa (e.g., F.turolensis) is interpreted to have developed in responseto water-stress associated with the seasonally aridclimate proposed by Ziegler et al. (1987).

4. Systematic palaeontology

Order: ConiferalesFamily: Miroviaceae Bose & Manum, 1990, p. 64.

Genus Mirovia Reymanowna emend. Bose & Manum,1990, p. 64.

Type species. Mirovia szaferi Reymanowna, 1985, p. 6.

Original diagnosis. See Bose & Manum (1990, p. 64).

Emended diagnosis. Leaves linear, helically arrangedand horizontally spreading; base tapering or decur-rent; apex obtuse, acute or apiculate. Adaxial surfacewith or without a median furrow; abaxial surface witha distinct median stomatal groove. Resin ductspresent. Cells of upper cuticle arranged in longitudi-nal rows, rectangular, trapezoidal or polygonal;anticlinal walls straight or slightly wavy, surface non-papillate. Abaxial surface cells outside median groovelike those of adaxial cuticle. Cells within mediangroove irregularly arranged, polygonal, shorter thancells outside groove; anticlinal walls straight; surfacewith or without papillae. Cells along margins ofmedian groove mostly papillate; papillae varying inshape and size, surface non-tuberculate; margins ofgroove projecting over stomatal area but sometimesonly weakly developed. Stomata confined to lowermedian groove, irregularly distributed or arranged infiles, longitudinally or obliquely orientated, rarelytransverse. Subsidiary cells 4–8, papillate or non-papillate. Guard cells sunken, thinly cutinized.

Remarks. The generic diagnosis provided by Bose &Manum (1990, p. 64) is slightly modified above totake into consideration the occurrence of: (1) morethan 2–3 resin ducts; (2) slightly wavy anticlinal wallsof some epidermal cells outside the stomatal groove;(3) sporadic development of weakly projectingstomatal groove margins; and (4) a wider rangeof subsidiary cell numbers. These refinements arederived from illustrations of the Mirovia species pro-vided by Bose & Manum and from the features of thenew species described here. Bose & Manum expresseddoubts about some of the specimens included inM. szaferi by Reymanowna (1985), because of theabsence of projecting margins over the stomatalgroove, but this concern seems unfounded. Notably,Bose & Manum (1990) included M. sibirica(Samylina) in the genus although this species does notpossess projecting margins (Manum, 1987, table 2).Thus, it appears that the development of project-ing stomatal groove margins is variably expressed inMirovia.

Figure 1. Mirovia gothanii sp. nov., Lower–Middle Albian, Rubielos de Mora, Spain. A, holotype, emarginate to mucronateapices, MPZ 00/566; � 4. B, bases with a proximal constriction and a decurrent insertion, MPZ 00/567; �4. C, adaxialcuticle devoid of stomatal apparatus and with rectangular epidermal cells in rows, MPZ 00/568; �75. D, abaxial cuticlecomporting a median stomatal groove bounded by lateral areas without stomata; the groove margins are projecting andoverhang the stomatal area, MPZ 00/568; �35. E, ordinary epidermal cells of the adaxial cuticle with wavy anticlinalwalls, MPZ 00/568;�280. F, set of stomata showing longitudinal or oblique orientations, MPZ 00/568; �330. G, distaltermination of the stomatal groove as a tip before the margin; the stomatal groove displays numerous papillae, MPZ00/568; �120. H, short conical papillae with generally rounded tops and stomata with papillate subsidiary cells, MPZ00/568; �230.

764 B. Gomez

A new species of Mirovia from Spain 765

Mirovia gothanii sp. nov.Figures 1–3

1954 Sciadopitytes sp. (? n. sp.), Gothan, p. 337, figs1–6.

1999 Pseudocycas sp., Gomez, Barale, Martın-Closas,Thevenard & Philippe, p. 661, fig. 17.

Derivation of name. From Dr Walther Gothan whofirst described Sciadopitys-like needles that are abun-dant in coals at Santa Maria de Meıa (Lleida province,Pyrenees, Spain).

Holotype. Museo Paleontologico de Zaragoza,Zaragoza, Spain, catalogue no MPZ00/566, EscuchaFormation, Rubielos de Mora locality, Teruelprovince (Gomez et al., 2002, text-fig. 2).

Paratypes. Light microscope slide nos. MPZ00/560–565, MPZ00/567–568 and SEM stub no. MPZ00/570.

Other material. Light microscope slide MPZ00/569and SEM stub MPZ00/571. Unnumbered materialincludes a large number of bases, middle parts andapices of leaves of variable length. Transversly brokenleaves are found dispersed in the clay layer of theexposure of the Escucha Formation at Rubielos deMora.

Stratigraphic range. Lower–Middle Albian.

Diagnosis. Linear leaf, up to at least 50 mm long,1.3–2.2 mm wide, tapering imperceptibly into a proxi-mal constriction just distal to abruptly swollen anddecurrent base. Apiculate to mucronate apex, com-monly missing. Stomatal groove depressed with over-hanging margins, up to 120 �m (average 50 �m),never exceeding one-fifth of the groove width; in somecases there are regions along this groove where thereare no overhanging margins. Groove in a point justbelow the apex. Cuticles 10–20 �m thick. Stomataldensity within the groove 140–170 per mm2. Stomatalorientation preferentially longitudinal. Stoma typically70–110 �m long and 60–90 �m wide. Stoma with 4–7subsidiary cells, one always in each polar position.

Subsidiary cells, non-stomatal cells inside the grooveand margins each bearing one single short bluntpapilla. Mesophyll with 3–7 resin ducts.

Description. The leaves are linear or slightly curved andhave parallel margins. They are 1.3–2.2 mm wide andprobably exceed 50 mm in length (Figure 1A, B). Thebasal insertion is represented by a triangular to rhom-boidal cushion 1.3–1.9 mm wide (Figure 1B). One ofthe edges is longer and may correspond to the lower-most decurrent part on the axis. Just above the inser-tion area the leaves are swollen, then suddenly becomenarrow (0.8–1.5 mm wide) to form a very distinctconstriction before widening gradually until theyreach their maximum width. The obtuse or slightlyacute apex is usually mucronate but the mucron iscommonly missing (Figure 1A).

The cuticles are 10–20 �m thick, the adaxial andabaxial sides being almost the same thickness. Onlythe abaxial side displays a median stomatal groove,which occupies 1/5–1/4 of the 0.3–0.5 mm leaf width(Figure 1F) and ends in a point just below the apex(Figure 1G). The margins of both sides overhang thestomatal groove, extending up to 120 �m (average50 �m) beyond the stomatal groove (Figures 1D, 3F).The stomata are scattered or tend to form discontinu-ous rows at the bottom of the stomatal groove (Fig-ures 1D, 2D, H). The stomatal density within thegroove ranges from 140 to 170 per mm2. The stomataare preferentially orientated longitudinally and only inrare cases obliquely (Figures 1F, 2H). The haplo-cheilic stomata are monocyclic with 4–(5–6)–7 sub-sidiary cells (Figure 3B, D), each subsidiary cellbearing one papilla (Figure 3A). There is always onesubsidiary cell in each polar position. The stomata areslightly oval and measure 70–110 �m long and 60–90 �m wide. The subsidiary cells measure 10–65 �m(average 25 �m) long and 9–18 �m (average 13 �m)wide, and are separated by anticlinal walls 1–2 �mthick. The non-stomatal cells in the stomatal grooveare small and rectangular to polygonal (Figure 2H).They are 17–35 �m (average 24 �m) long and4–20 �m (average 11 �m) wide. Their anticlinal wallsare 2–6 �m thick. The ordinary epidermal cells of theabaxial side, outside the stomatal groove, are arranged

Figure 2. Mirovia gothanii sp. nov., Lower–Middle Albian, Rubielos de Mora, Spain. A, external view of the adaxial cuticle,MPZ 00/570;�80. B, internal view of the adaxial cuticle, MPZ 00/570;�40. C, external view of the abaxial cuticleshowing the median stomatal groove, MPZ 00/570;�40. D, internal view of the abaxial cuticle showing the medianstomatal groove, MPZ 00/570;�40. E, external view of the stomatal groove and the numerous short papillae that fill it,MPZ 00/571;�270. F, internal view of the adaxial cuticle with hair bases and wavy anticlinal walls, MPZ 00/571;�150.G, internal view of the abaxial cuticle showing the epidermal cells of the lateral non-stomatal areas arranged in rows withwavy anticlinal walls, MPZ 00/570;�150. H, stomatal strip with longitudinally or obliquely orientated stomata, MPZ00/570;�150.

766 B. Gomez

A new species of Mirovia from Spain 767

in serial longitudinal rows (Figures 1D, E, 2G). Theyare rectangular to trapezoid in shape, 45–160 �m(average 92 �m) long and 9–35 �m (average 22 �m)wide. They show slightly wavy anticlinal walls 2–8 �mthick. The ordinary epidermal cells of the projectingmargins, the slopes and the bottom of the stomatalgroove bear short, rounded to conical papillae withblunt tops (Figures 1G, H, 2C, E, 3C, E, F). Thesepapillae measure 13–23 �m (average 18 �m) long and9–20 �m (average 16 �m) wide at the base.

The adaxial side shows a median wrinkle (Figure2A). This side is completely devoid of stoma (Figures1C, 2A, B). The epidermal cells are arranged inlongitudinal rows and tend to converge when thewidth diminishes towards the apex. The cells aresquare, rectangular, trapezoidal or polygonal (Figure2B, F), 25–105 �m (average 50 �m) long and 10–50 �m (average 25 �m) wide. They display slightlywavy anticlinal walls 2–8 �m thick.

Inside the mesophyll 3–7 (average 5.5) resinducts run along the length of the lamina (Figure3G, H).

Comparisons. Mirovia gothanii differs from Sciado-pityoides Sveshnikova emend. Bose & Manum (1990,p. 21) in the shape of the basal lamina just above thepoint of attachment: M. gothanii has a slight constric-tion but Sciadopityoides has parallel margins and noconstrictions (Table 1). Unlike M. gothanii, themonospecific genus Holkopitys Bose & Manum (1990,p. 49) displays two stomatal strips protected in asingle groove with prominent margins where cells ineach strip lack papillae (Table 1). In contrast to M.gothanii, the stomatal groove in Oswaldheeria Bose &Manum (1990, p. 39) is not depressed (Table 1). Theclosest resemblance exists between the new Spanishmaterial and members of Mirovia Reymanownaemend. Bose & Manum (1990, p. 64). However, sixout of eight Mirovia species have leaf lengths of lessthan 15 mm (Table 1). The two other species aredistinguishable from M. gothanii by: (1) the presenceof longer ‘finger-like’ papillae on the projecting mar-gins in Mirovia persulcata (Johansson) Bose &Manum, and (2) the absence of a projecting orpapillate groove (see Manum, 1987, table 2 and Bose

& Manum, 1991, table 1 respectively) in Miroviasibirica (Samylina) Bose & Manum.

According to the illustrations in Gothan (1954),Sciadopitytes sp. from the Lower Cretaceous of SantaMaria de Meia are in accordance with the specimensdescribed here in many features: (1) width of theleaves (1.7–2.2 mm); (2) width of the stomatal groove(0.4–0.5 mm; Gothan, 1954, figs 1–2); (3) occurrenceof an obtuse, emarginate apex (top of fig. 2 in Gothan,1954) or with its mucron preserved (on the right offig. 1 in Gothan, 1954); (4) stomatal groove weaklycovered by margins (up to 70 �m); (5) stomatal den-sity about 150 stomata per mm2; (6) high density ofpapillae (fig. 4 in Gothan, 1954); and (7) shortpapillae (1.5–3.5 �m long) rounded at their top (fig. 5in Gothan, 1954). This new assignation of Gothan’s(1954) specimens was also proposed by Manumet al. (2000) who suggested close affinities with M.persulcata.

Remarks. The linear leaves of Mirovia gothanii shareseveral characters with the modern Sciadopitys verticil-lata: (1) the stomatal area is restricted to a more or lessprotected groove, and (2) each non-stomatal cell andeach subsidiary cell of the stomatal strip bears onepapilla, and these papillae protect the stomata (Halle,1915, p. 511; Reymanowna, 1985, p. 8). The leavesof Sciadopitys verticillata are, however, of two types:(1) brown, scale-like leaves spirally-arranged along theaxis or disposed in very tight false whorls in the distalpart, and (2) linear leaves with a single stomatalgroove borne by small dwarf twigs. These ‘symphyl-lodes’ would have originated from the fusion of twoleaves, the groove corresponding to the junction oftheir lower sides (Meyen, 1987, p. 212). Bose &Manum (1990, p. 17) found no evidence in the mor-phology of Mirovia leaves or shoots that favour such aphenomenon. In contrast to Sciadopitys verticillata, theleaves of M. gothanii are not dimorphic in venation orin stomatal distribution. None of the miroviaceousspecies possesses the leaves borne by small dwarf twigsor the pseudo-whorled leaf arrangement present inSciadopitys verticillata (Bose & Manum, 1990, p. 14;Taylor & Taylor, 1993, p. 712), but evidence fromdenuded stems, leafy twigs, and the character of the

Figure 3. Mirovia gothanii sp. nov., Lower–Middle Albian, Rubielos de Mora, Spain. A, stoma in external view showing shortpapillae around the mouth of the stomatal pit, MPZ 00/571;�600. B, stomatal apparatus with seven subsidiary cells,MPZ 00/570;�600. C, inside of the stomatal groove in external view with papillae, MPZ 00/571;�320. D, two stomatain external view showing four and six subsidiary cells respectively around the guard cells, MPZ 00/570;�600. E,projecting and overhanging stomatal groove margin with papillae, MPZ 00/571;�320. F, non-projecting andnon-overhanging stomatal groove margin with papillae, MPZ 00/571;�750. G, resin canals in the leaf mesophyll, MPZ00/569;�60. H, SEM of a resin canal, MPZ 00/571;�320.

Tabl ose & Manum, 1990, 1991 and Manum et al., 1991)

Chara

Miroviaineffecta

Bose & Manum

Mirovialagerheimii

(Johansson)Bose & Manum

Miroviapersulcata

(Johansson)Bose & Manum

Miroviasibirica

(Samylina)Bose & Manum

Decur + + + +Hole iStoma + + + +StomaStoma + + + +StomaFurrow � + ? ?Leaf d +StemsLength 10–12 10–15 50+ 40+Resin + + ? ?Groov + � + �Stoma + + +StomaStomaStoma +Subsid + + + +Margin + + + �Papilla + + ?Non-s � � � �

Locati Spitsbergen, BaffinIsland

northern Norway northern Norway Siberia

Age Barremian–Aptian Bajocian–Bathonian Bajocian–Bathonian Early Cretaceous

Refere Bose & Manum(1990)

Johansson (1920);Florin (1922);Sveshnikova (1981);Manum (1987);Bose & Manum(1990)

Johansson (1920);Florin (1922);Sveshnikova (1981);Manum (1987);Bose & Manum(1990)

Samylina (1963);Sveshnikova (1981);Manum (1987);Bose & Manum(1990)

768B

.G

omez

e 1. Comparison of the species belonging to the family Miroviaceae (modified from B

cters/Taxa

MiroviacapbohemanensisBose & Manum

Miroviaflorinii

Bose & Manum

Miroviagroenlandica

Bose & Manum

rent leaf base + + +n bottom of leaftal zone in groove + + +tal zone not in grooveta irregularly arranged + + +ta in files or bands

in upper surface � � �imorphism documented + +, denuded (D) or leafy (L) L

of leaf (mm) 8–15 7–15 7–10ducts + + �e margin papillate + + +ta orientated longitudinally + +ta orientated transversely (+)ta orientated obliquely + (+)ta randomly arrangediary cells papillate � + �s projecting over stomatal groove + + +e towards groove longer + + +tomatal cells inside groove with papillae (+) (+) �

on Spitsbergen Spitsbergen, BaffinIsland

West Greenland

Barremian–Aptian Barremian–Aptian Barremian–Aptian

nces Bose & Manum(1990)

Bose & Manum(1990)

Bose & Manum(1991)

caOswaldheeria hallei

(Florin)Bose & Manum

Oswaldheeriamacrophylla

(Florin)Bose & Manum

Oswaldheeria scotica(Florin)

Bose & ManumHolkopitys hoegiiBose & Manum

+ + + +

++ + ++ + +

(+) (+) ++ + � �+D

10–20 50 90 15–20+ + + ?� � � �+ + + +

� + � �� � � +� � � +� + � �

West Greenland,Baffin Island,Spitsbergen

northern Norway Scotland Baffin Island,Spitsbergen

Barremian–Aptian Bajocian–Bathonian Late Jurassic Barremian–Aptian

Florin (1922); Bose& Manum (1990)

Florin (1922);Sveshnikova (1981);Manum (1987);Bose & Manum(1990)

Florin (1922); Bose& Manum (1990)

Bose & Manum(1990)

Anew

speciesof

Mirovia

fromS

pain769

Table 1. Continued

Characters/taxa

Mirovia szaferi(Reymanowna)Bose & Manum

=type speciesMirovia gothanii

sp. nov.Oswaldheeria arcti

Bose & Manum

Decurrent leaf base + + +Hole in bottom of leafStomatal zone in groove + +Stomatal zone not in groove +Stomata irregularly arranged + +Stomata in files or bands +Furrow in upper surface + + +Leaf dimorphism documented +Stems, denuded (D) or leafy (L)Length of leaf (mm) 10–14 50+ 8–15(�22)Resin ducts + + +Groove margin papillate ? + �Stomata orientated longitudinally + + +Stomata orientated transverselyStomata orientated obliquely (+) (+)Stomata randomly arrangedSubsidiary cells papillate � + +Margins projecting over stomatal groove + + �Papillae towards groove longer ? � �Non-stomatal cells inside groove with papillae � + �

Location Poland Spain Baffin Island,Spitsbergen

Age Early Bathonian Albian Barremian–Aptian

References Reymanowna(1985); Bose &Manum (1990)

herein Bose & Manum(1990)

T

C

Sciadopityoidesnathorstii(Halle)

Sveshnikova

Sciadopityoidesukrainensis

Doludenko &Sveshnikova

Sciadopityoidesuralensis

(Dorofeev &Sveshnikova)Sveshnikova

Sciadopityoidesvariabilis(Bose)

Sveshnikova

DH + + + +S + + + +SS + + + +S (+)F � ? ? �LS DL 40–50 (6�)12–15(�24)R +G + �S +SSS +S (+) �Mst

+ �? + +

P � �Nw

� � + �

L West Greenland Western Ukraine Urals Baffin Island

A Barremian–Aptian Late Jurassic Cenomanian–Turonian

Barremian–Aptian

R Halle (1915);Sveshnikova(1981)

Doludenko (1963);Sveshnikova(1981); Manum(1987)

Dorofeev &Sveshnikova (1959);Doludenko (1963);Sveshnikova (1981);Manum (1987)

Bose (1955);Sveshnikova(1981)

770B

.G

omez

able 1. Continued

haracters/taxa

Sciadopityoidescrameri(Heer)

Sveshnikova

Sciadopityoidesgreenboana

Watson et al.

Sciadopityoidesikorfatensis

Bose & Manum

Sciadopityoidesmicrophylla

(Heer)Bose & Manum

ecurrent leaf baseole in bottom of leaf + + + +tomatal zone in groove + (+) + +tomatal zone not in groove +tomata irregularly arranged + + +tomata in files or bands +urrow in upper surface + ? + �eaf dimorphism documented + + +tems, denuded (D) or leafy (L) D Length of leaf (mm) 7–18 9 13–18 10–14(�20)esin ducts + +roove margin papillate + + +tomata orientated longitudinally + +tomata orientated transversely + +tomata orientated obliquely + +tomata randomly arrangedubsidiary cells papillate - (+) � �argins projecting over

omatal groove+ � + +

apillae towards groove longer (+) + +on-stomatal cells inside grooveith papillae

� +

ocation West Greenland England West Greenland Baffin Island,Spitsbergen,West Greenland

ge Barremian–Aptian Berriasian–Hauterivian

Barremian–Aptian Barremian–Aptian

eferences Heer (1868,1876); Halle(1915);Sveshnikova(1981)

Watson et al.(2001)

Bose & Manum(1990)

Heer (1876);Bose & Manum(1990)

A new species of Mirovia from Spain 771

leaf bases in detached leaves show that the leaves werespirally attached or horizontally spreading (e.g., Bose& Manum, 1991, p. 19). There is no evidence tosuggest that small leaves (scale leaves) subtended largeleaves (needles) as in the extant species. Moreover,the stomata of Sciadopitys verticillata adult leaves donot have the same structure (Watson & Harrison,1998, fig. 16C) as those of the Miroviaceae and, inparticular, show 8–13 (14) subsidiary cells (Florin,1931; Lemoine-Sebastian, 1972) in contrast, forexample, to Mirovia gothanii which only displays 4–7subsidiary cells.

In accordance with the hypothesis of Bose &Manum (1990, p. 17) concerning Mirovia andOswaldheeria, the decurrent tapered base and the leafcushion of Mirovia gothanii suggest that the leaves ofthe latter could have been arranged horizontally.However it is difficult to ascertain whether they weredeciduous like many other Mesozoic ‘Sciadopitys-like’taxa mentioned above (Manum et al., 2000) or per-sistent, being only separated after the death of theshoot as observed in Taxus baccata L. (pers. obs.).

The exact evolutionary relationships betweenextinct and extant gymnosperm families remaincontroversial and one may question whether theMiroviaceae are sufficiently distinct to be recognizedas a separate family (Watson et al., 2001). Among theliving conifers the closest affinities of the Miroviaceaeare undoubtedly somewhere within the Cupressaceaesensu stricto, Sciadopityaceae or Taxodiaceae, whichdepending on systematic treatments, are considered tobe three distinct families (Price, 1989; Page, 1990;Ohsawa, 1994), or two, with the Sciadopityaceaeincluded as a subgroup of the Taxodiaceae (Hart,1987; Stewart & Rothwell, 1993; Taylor & Taylor,1993; Yao et al., 1997) or with the Taxodiaceaecompletely merged into the Cupressaceae sensu lato(Eckenwalder, 1976; Brunsfeld et al., 1994, Gadeket al., 2000). So, in the current state of the art, theassignation of ‘Sciadopitys-like’ fossil leaves to one orother of the extant families may introduce moreconfusion than clarity. Otherwise, the fossil record ofconifers suggests that the Taxodiaceae originated dur-ing the Triassic and was well established by theJurassic (Lemoigne, 1967; Miller, 1982; Yao et al.,1997), and that the Cupressaceae may have had itsorigin in this family (Alvin et al., 1982). Oxfordiantaxodiaceous woods, along with known reproductivestructures (Yao et al., 1997, 1998), reinforce the viewthat this family was well separated from Cupressaceaeby the Middle Jurassic (Philippe, 1994). Whateverthe phyletic history was, a few living cupressaceousand taxodiaceous taxa display acicular/linear leaves.

Acicular leaves of Juniperus L. (Cupressaceae sensu

stricto) bear one (e.g., J. conferta Parl or rigida Sieb. &Zucc.) or two (e.g. J. communis L., drupacea Labille oroxycedrus L.) stomatal bands, but the stomata arenever set in a groove as in Holkopitys, Miroviaand Sciadopityoides. Juniperus leaves generally remainattached to the stem even long after their death. Inaddition, living relatives of Juniperus (e.g., J. com-munis or oxycedrus) usually have strongly keeled leaveswith well-developed sclerenchyma joining the adaxialand abaxial surface, which would probably be pre-served during fossil diagenesis, but they havenever been observed in the Miroviaceae. Within theTaxodiaceae, Athrotaxis selaginoides D. Don, Cunning-hamia (Richard) Brown, Glyptostrobus Endlicher,Metasequoia Miki, Sequoia Endlicher, and TaxodiumRichard have linear or lanceolate leaves. Taxodiaceaeusually show amphistomatic leaves, except forMetasequoia glyptostroboides Hu & Cheng, with stomataarranged in bands or more exceptionally scatteredin Athrotaxis cupressoides D. Don, Glyptostrobuslineatus (Poir.) Druce, and Sequoiadendron giganteum(Lindley) Buchholtz (Srinivasan & Friis, 1989).However, none of these has the typical single stomatalgroove of the Miroviaceae and, thus, I am inclinedhere to prefer the genus Mirovia and the familyMiroviaceae in the sense of Manum et al. (2000)rather than the Sciadopityoides form-genus concept ofWatson et al. (2001). The Miroviaceae constituted asignificant group in Early Cretaceous Arctic floraswhen the family reached its climax in terms of abun-dance and diversity (Manum, 1987, p. 21). Somesporadic occurrences extending into Eurasia areknown from the mid-Jurassic–Late Cretaceous (Bose& Manum, 1990). Other data from the EnglishWealden have demonstrated the occurrence of theMiroviaceae in Western Europe: Sciadopitytes sp. nov.(31TaxodSc; Oldham, 1976, p. 462, pl. 73, figs 1–6)and Sciadopityoides greenboana Watson et al. (2001).Data from Rubielos de Mora now establish that itsgeographical expansion reached southern parts of theNorthern Hemisphere (approximately the Albian30�N according to Smith et al., 1994), even belowthe present 40�N postulated by Florin (1963) andSveshnikova (1981). At Rubielos de Mora, as well asat Santa Maria de Meia, Mirovia gothanii constituted adominant component of the flora. There are likely tobe palaeoecological and palaeoenvironmental expla-nations for the success of the family during the EarlyCretaceous. Strong xeromorphic adaptations areexpressed in the absence of stomata on the adaxialside while, on the abaxial cuticle, they are arrangedclose to each other in a single strip sunken into agroove with a protruding margin, and are protectedby papillae. In Spain the success of M. gothanii may

772 B. Gomez

have been related to a unique set of climatic andedaphic conditions (Gomez et al., 1999, p. 673). Onthe other hand, as noted by Manum et al. (2000,pp. 226, 227), the apparent paradox of xeromorphicadaptations of the Miroviaceae in non-xeric habitatsfrom Spain to the Arctic during the Jurassic–Cretaceous period can be interpreted as ‘a phylo-genetically conservative feature of gymnosperms ingeneral or more specifically as a functional adaptationto less efficient water conductive system’.

Acknowledgements

This research was supported by a European Commu-nity Marie Curie Fellowship (HPMF-CT-2002-01584), by UMR 5125 and the ECLIPSE programmeof the French CNRS, and by Spanish Governmentprojects BTE2001-0185-C02-01 and B052001-0173.I thank the referees and editor for their comments onthe original manuscript.

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