Protophyllocladoxylon holbavicum, Iamandei & Iamandei & Grădinaru, 2018

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 : 21-23

Protophyllocladoxylon holbavicum sp. nov.

Fig. 9 a-i.

The studied material

The studied material is represented by a sigle decimetric sized sample of silicified wood found in Holbav area, on the Maiului brook, in Lower Jurassic continental pyroclastic deposits considered of Pliensbachian age. The studied sample represents a trunk fragment, having dark to black color and by magnifying glass or even by naked eye, regular fibrous structure without vessels is visible, suggesting a coniferous wood. The specimen with the field number 1040 belong to "Grădinaru Collection" and is deposited now under the inventory number 27644 in the collections of the Geological Institute of Romania ( G. I. R. Collections), hosted by the National Geological Museum, Bucharest.

Microscopic description

The studied specimen has s e c o n d a r y w o o d with tracheidoxylic structure devoid of any normal or traumatic resin canals, with diminishing tracheid size only in the last part of the transitional wood close to the late wood,

which is represented by few rows of smaller tracheids, marking distinctly the growth ring boundary.

T r a c h e i d s - with polygonal in cross-section and polygonal lumina, slightly rounded at corners, have radial/tangential diameters of 20-40/20-45 μm and relatively thick walls, of 4-10 μm double wall. The interradial bundles have 1-9 radial regular rows of tracheids and the density is 784-899 tracheids per mm2. Tangentially seen the tracheids are usually unpitted, but sometimes small circular pits of 8-12 μm in diameter, in a single vertical row appear. Radial pitting is of mixed type, almost exclusively uniseriate, with pits circular, spaced or contiguous, with round or oblique elliptic apertures. When contiguous they are slightly flattened. The pits have round borders of 17-21 μm and rounded to tilted elliptical apertures of 5- 7/3-4 μm. There are no crassulae or helical thickenings .

A x i a l p a r e n c h y m a - appears in cross-section as few, disperse cells relatively thick-walled, difficult to distinguish of tracheids, but visible in tangential view, having thick terminal (horizontal) walls.

M e d u l l a r y r a y s - are fine, rectilinear in cross-section, with smooth horizontal cellular walls. Tangentially the rays have 1-21 cells in height, or more, i.e. 30- 550 μm high. The taller rays have high biseriations (up to ten storeys) giving to the rays a biseriate aspect with long uniseriate endings. The ray cells are polygonal rounded to oval and have relatively thick walls. Ray density is 8-12 rays on horizontal tangential millimeter. Radially the rays are homocellular, cells all procumbent of 20-30 μm high, moderately thick-walled: 5-6.2 μm the double wall. The tangential walls are thick-walled or slightly nodular. Indentures indistinct or absent. The typical cross-fields have 1-2 oopores of phyllocladoid type, more or less bordered, and inclined, of 13-17 μm in diameters, with large lens-like apertures of 6.5-8.5/3-5 μm .

Affinities and discussions

The here studied sample of fossil wood presents tracheidoxylic structure with uniseriate rays, pitting of mixed type on the radial tracheidal walls and phyllocladoid cross-fields, aspects which suggest similitude with members of the Family Podocarpaceae Endlicher, 1847 , especially with the extant Phyllocladus Rich. ex Mirb. , and send to the fossil correspondent Protophyllocladoxylon (Kräusel) Vogellehner, 1968 , a type of tracheidoxylic Mesozoic fossil wood having such characters. In fact the species described from the Cretaceous of Syria ( P. leuchsii ) and designated as type-species by Kräusel (1939), has some problems of origin, age and anatomy (Philippe et al., 2003; Pujana, 2005), so a reappraisal of this genus is necessary.

The correct diagnosis of the genus Protophyllocladoxylon (Kräusel, 1939) as is emended by Vogellehner (1968), is presented by Philippe (1995) like this: "Tracheidoxyl without secretory canals, with radial pitting of mixed type and cross-fields with 1-2 elliptic oopores to large oval, more or less oblique, horizontal ray-cells walls integer". Or, as it's specified by Philippe & Bamford (2008), "oopore more phyllocladoid (i.e. pointed and oblique), usually somewhat bordered in the latewood". In fact, large, oval, more or less oblique oopores are present in the cross-fields only to Protophyllocladoxylon , but not to Xenoxylon, Protocircoporoxylon or Prototaxodioxylon , where other types of oopores appear.

We tried a comparative analyse of our studied specimen with some already described forms from worldwide because during Paleozoic and Mesozoic times it seems that this genus had a widespreading, and we cite:

- Paraphyllocladoxylon araucarioides Holden, 1913b , was relatively badly described and, having araucarian characters, is possibly to be reconsidered as Protophyllocladoxylon (Philippe & Bamford, 2008) . In fact, these authors specified that the groups of Paleozoic and Mesozoic described species of Protophyllocladoxylon have araucarian characters and must be recognized and a reappraisal of this genus is necessary.

- Also, numerous species of Protophyllocladoxylon described before 2003 felt in synonymy with Metapodocarpoxylon libanoticum (Edwards) Dupéron- Laudoueneix et Pons, aspect discussed in detail by Philippe et al. (2003) and Philippe & Bamford (2008).

- Protophyllocladoxylon quedlinburgense Schultze-Motel, 1961 has flattened radial uniseriate pitting and also biseriate opposite, so it's slightly different of our material.

- Protophyllocladoxylon franconicum was described from Germany by Vogellehner (1966) is a Mesozoic form with phyllocladoid type of oopores and with radial uniseriate pitting, rather similar to our specimen .

- More recently, Zhang Yi et al. (2010) have described a Paleozoic species: Protophyllocladoxylon jingyuanense , from Carboniferous (Late Mississipian) deposits from NW China, with similar features in radial pitting and in cross-fields.

- Boura et al. (2013) described some Early Cretaceous woods from Vietnam beside some species of other gymnosperms, a Protophyllocladoxylon xalucense , a new species bearing all the typical features of the genus and more than that, an abundance of axial parenchyma. Also, a documented comparison with numerous species of Protophyllocladoxylon described in far-eastern Asia was done, all of them different of our specimen.

- Also , Fletcher et al. 2014 have described a Protophyllocladoxylon owensii as a new species from the Upper Cretaceous of Queensland ( Australia), having radial pitting on the tracheid predominantly alternate and contiguous (of araucarian type), uniseriate in latewood, biseriate and rarely triseriate, in earlywood, but the cross-field pits are typically phyllocladoid and have oopores or more rarely circopores, two per cross-field in earlywood, one in latewood .

- Pujana et al. (2014, 2015) described a Palaeocene and Eocene species of Protophyllocladoxylon from Antarctica, with tracheid radial pitting uniseriate to biseriate, rarely triseriate, sometimes scattered and mostly contiguous, opposite to alternate, so, of mixed type with pits circular to hexagonal, usually flattened. The axial parenchyma is absent. Cross-field pitting is fenestriform, with 1-2 large oopores (simple pits) per cross-field, so it's very different of our material.

- Vajda et al. (2016) described a permineralized conifer wood attributed to Protophyllocladoxylon sp. , from Korsaröd, southern Sweden, from some volcaniclastic deposits associated to a Jurassic volcanism, and tried palaeoclimatically the presence of such an exotic taxon in the Sweden Jurassic.

Our specimen has a tracheidoxylic structure, radial pitting of mixed type, usually uniseriate, with round pits, spaced or contiguous (when flattened), parenchyma with thick terminal (horizontal) walls, and uniseriate rays with high biseriations and phyllocladoid cross-fields, with 1, sometimes 2 oopores of phyllocladoid type, inclined, and with large lens-like apertures.

All these details define a special form of Protophyllocladoxylon , and analysing them in comparison with other valid species presented above we think we are faced with a new species that we named Protophyllocladoxylon holbavicum sp. nov., after the name of the locality area from where it was found. The studied specimen designated holotype has the inventory number 27644 (field number 1040) and is now deposited in G.I.R. Collections, in the National Geological Museum in Bucharest.

Diagnosis of the new species Protophyllocladoxylon holbavicum sp. nov.

Secondary wood with tracheidoxylic structure without any canal, with distinct growth-ring boundary, marked by few rows of smaller tracheids. Tangentially seen the tracheids usually unpitted, but sometimes small circular pits in a single vertical row appear. Radial pitting is of mixed type, usually uniseriate with pits circular, spaced or contiguous, with round or oblique elliptic apertures. When contiguous they are slightly flattened. Axial parenchyma few, disperse, with thick terminal (horizontal) walls. Medullary rays uniseriate, the taller ones with high biseriations giving aspect of biseriate rays with long uniseriate endings, radially homocellular, tangential walls are thick-walled or slightly nodular, no indentures and cross-fields with 1-2 phyllocladoid oopores, bordered, inclined, with large lens-like apertures.

Figures

Fig. 9 Protophyllocladoxylon holbavicum sp. nov. - holotype - inventory no. 27644 (field no. 1040). a-c Cross-section: distinct growth-ring boundary, polygonal tracheids with rounded corners, and linear rays. d-f Tangential section: unpitted tracheids, uniseriate rays, and biseriate with long endings. g-i Radial section: uniseriate radial piting on tracheids of mixed type, phyllocladoid cross-fields with 1-2 phyllocladoid large inclined oculipores.