Palaeoginkgoxylon Feng, Wang et Rössler, 2010

Iamandei, Stănilă, Iamandei, Eugenia & Grădinaru, Eugen, 2018, Contributions To The Study Of The Early Jurassic Petrified Forest Of Holbav And Cristian Areas (Brașov Region, South Carpathians, Romania). 1 Part, Acta Palaeontologica Romaniae 14 (2), pp. 3-34 : 23-26

Genus Palaeoginkgoxylon Feng, Wang et Rössler, 2010 Palaeoginkgoxylon sp.

Fig. 10 a-i; Fig. 11 a-i.

The studied material

The studied material is represented by three decimetric-sized samples of silicified wood, two found in the Holbav locality area (South BraȘov County), on the Maiului brook and one around Cristian locality, on the Fabricii valley, in the Early Jurassic continental deposits maybe with pyroclastic character considered of Sinemurian- Pliensbachian age, most probably Pliensbachian. The studied sample represent trunk or thick-branch fragments, having dark to black color and by magnifying glass or even by naked eye, regular fibrous structure without vessels suggesting a conifer wood. The specimens with field-numbers 1011, 1023, 1017Cr - in "Grădinaru Collection", are deposited now under the inventory numbers 27645 - 27747 in the collections of the Geological Institute of Romania ( G. I. R. Collections), hosted by the National Geological Museum in Bucharest.

Microscopic description

Both the studied specimens present s e c o n d a r y w o o d with tracheidoxylic structure, with relatively thick-walled tracheids and few parenchyma, devoid of any resin canals, and with quite indistinct growth-rings boundaries, relatively badly preserved (1017).

T r a c h e i d s - with polygonal cross-section with slightly rounded corners, unequal in size, with polygonal or quadrangular rounded lumina gradually diminishing in size from early to late wood, having radial/tangential diameters of 25-35)/25(35-40) μm, smaller in the late wo- od, and not too thin-walled, of 4-7 μm double wall thicker in the late-wood. The interradial bundles have 2-12 radial regular rows of tracheids and the density is 1360- 1728 tracheids per mm2. Tangentially seen the tracheids are usually unpitted, rarely uniseriate pitted and with the terminal parts slightly leaned over the neighbor cells. Radial pitting is of mixed type, with pits either polygonal to slightly rounded, spaced or contiguous, in one vertical row, or less, biseriate, alternate or slightly irregular to opposite. The bordered pits are polygonal to rounded, slightly flattened, relatively small, of 8-10 μm in diameter when biseriate, and round of 10-16 μm in diameter, also slightly flattened when uniseriate. Often only the pit chamber is visible, the aperture difficult to observe is small round to short elliptic, of 1.5-2(3.5) μm. Crassulae or helical thickenings were not observed. Sometimes the tracheids have bent ends which overlap each other (specimen 1017Cr) and bear some dark content inside lumina . A x i a l p a r e n c h y m a - appears sometimes like few dispersed cells in transversal view and isolated or in short vertical rows usually, difficult to observe due to bad preservation.

M e d u l l a r y r a y s - are fine, rectilinear in tranversal view. Simple pits irregularly arranged could appear on the horizontal walls. Tangentially the usually uniseriate rays have 1-7(-16) cells in height, i.e. 20-180(-350) μm high. Sometimes the taller rays have 1-5 biseriate storeys, giving an almost biseriate aspect (specimen 1023). The ray cells are round to oval and have moderately thin walls, of 2.5-3 μm double walls. Simple pits irregularly present on the tangential walls. Ray density is 7-12 rays on horizontal tangential millimeter. Radially the rays are homocellular, cells all procumbent of 19-20(-28) μm high, moderately thick-walled: 5-6.2 μm the double wall. Within the marginal rows the cells are slightly higher, of 28-30(-40) μm. The cross fields of cupressoid type have 1-4(6-9?) oculipores, rounded or oval of 4-8(13) μm in diameter, with circular or short elliptic tilted apertures of 1-2(3.5) μm. Their arrangement is alternate or slightly irregular on 1-3 rows. Sometimes the walls of ray cells seem to be slightly wrinkled, but few details can be observed, due to the bad preservation .

Affinities and discussions

The presence of some xylotomical details of the secondary wood in our specimens like the presence of bent tracheids' ends overlapping each other and the presence of parenchyma suggested us a possible affinity with some fossil ginkgophyte trunks described from different Mesozoic sites in the world also mainly in the Asian space, in Mesozoic deposits, but in other. As is well known, only a species of ginkgophyte ( Ginkgo biloba L.) survived, li-

ving now, naturally, in China.

Some fossil taxa show xylotomical details similar to extant Ginkgo wood anatomical structure, as Ginkgoxylon ( Saporta, 1884) Philippe et Bamford, 2008 ), Proginkgoxylon (Khudajberdyev, 1971) Zheng et Zhang 2008 (in Zheng et al., 2008), Szeioxylon Wang, Jiang et Qin, 1994 , Sinopalaeospiroxylon Zhang et Zheng, 2006 (in Zhang et al., 2006), Primoginkgoxylon Süss, Rössler, Boppré et Fischer, 2009 ; Palaeoginkgoxylon Feng, Wang et Rössler, 2010 .

Taking into account the diagnosis of the genus Palaeoginkgoxylon Feng, Wang et Rössler, 2010 which specify that, beside the primary structure with pith, there is an well developped secondary xylem - which is pycnoxylic (i.e. tracheidoxylic) with size and slightly irregular arrangement of the tracheid, which, vertically have bent ends overlapping each other, have mixed radial pitting 1-2 seriate, cross-field pits cupressoid, ray cells irregularly pitted on the horizontal and the radial walls and also, and have axial parenchyma - we observed that our studied specimens, even if badly preserved, exhibit more similar features (regarding the tracheidal pitting usually 1-2 seriate, the cupressoid cross fields, the parenchyma), with the secondary wood of the species Palaeoginkgoxylon zhoui Feng, Wang et Rössler, 2010 , than with other above cited fossil genera.

Thus, based on these similitudes with the type species of a new genus described by Feng et al. (2010), we have attribute the studied material (3 specimens) to Palaeoginkgoxylon sp. , hoping to find a better preserved material and to document, at specific level, the presence of a ginkgophyte wood in the Jurassic flora of the Romanian Carpathians. In this context it's good to remark that Czier (1998a) described Ginkgo foliage from the Jurassic of the Carpathian Basin and such identification could support as acceptable Czier's proposal regarding the transfer of Ginkgoites and Baiera to the genus Ginkgo , because in addition to the similar foliage structure of these genera, our Jurassic material xylotomically is very similar the extant Ginkgo wood.

Figures

Fig. 10 Palaeoginkgoxylon sp. - material - inventory no. 27746 (field no. 1023). a-c Cross section: indistinct growth-ring boundary, thick-walled polygonal tracheids with rounded corners, and linear rays. d-f Tangential section: unpitted tracheids, uniseriate rays, and biseriate with long endings; polygonal-rounded ray-cells. g-i Radial section: radial piting on tracheids of mixed type, cross-fields with 1-2 rows of oculipores.

Fig. 11 Palaeoginkgoxylon sp. - material - inventory no. 27747 (field no. 1017cr). a-c Cross section: less distinct growthring boundary, thick-walled polygonal tracheids with rounded corners, and linear rays. d-e Tangential section: tracheids with bent ends, uniseriate rays. f-i Radial section: tracheids have bent ends which overlap each other, radial piting on tracheids of mixed type, bad preserved cross-fields.