Protojuniperoxylon holbavicum, Iamandei & Iamandei & Grădinaru, 2022

Iamandei, Stanila, Iamandei, Eugenia & Grădinaru, Eugen, 2022, Contributions To The Study Of The Early Jurassic Petrified Forest Of Holbav And Cristian Areas (Brașov Region, South Carpathians, Romania), 2 Part., Acta Palaeontologica Romaniae 18 (1), pp. 25-48 : 29-31

Protojuniperoxylon holbavicum sp. nov.

Fig. 2 , a-j.

Material

The studied material is represented by 7 samples of silicified wood, collected from the Holbav area, on Maiului brook. All studied samples are fragments of trunk or thick branches, of decimetric size, dark to black color. Viewing through a hand lens, or even by naked eye, it is possible to see the regular fibrous structure without vessels, which indicate a conifer wood. The specimens attributed to this species have very similar details and have the following field numbers within the "Grădinaru Collection": 1078, 1083, 1085, 1087, 1091, 1095, 1110 – and are stored at the National Museum of Geology, in Bucharest, under the inventory numbers: 27704 , 27705 , 27706 , 27707 , 27708 , 27709 , 27710 .

Microscopic description

Growth rings – well developed in the studied samples, representing the secondary xylem which is tracheidoxylic, showing a fairly gradual transition but sometimes abrupt, from early- to late-wood, and has distinct growth ring boundaries. Normal or traumatic axial resin canals are absent.

Tracheids – in cross section appear quasi-polygonal, usually quadrangular, and with moderately thick walls in the early-wood. They have radial / tangential diameters of 25-60 / 25-55 μm in the early- wood and wall thickness of 3-7 μm double wall. When gradual transition is present, the tracheids gradually diminish in section and usually the tracheidal wall in the late-wood becomes slightly thicker, of 7-9 μm in the final 3-8 rows of smaller sized and radially flattened cells, with r/tg diameters of 10-25 / 20-25 μm, marking the growth- ring boundary. Between two successive rays, 2-12 radial rows of tracheids can be counted. The density ranges 750-1216 tracheids / mm 2. Longitudinally, the tracheids have, on the radial walls, uniseriate pits, often with biseriate portions, often contiguous, or biseriate of mixed type, sometimes separated by crassulae. The pits are of abietinean type, have 14-21 μm in diameter and round apertures of 4-5 μm. Details on torus not observed. On the tangential walls, pits are usually absent. Organic deposits - absent. Average tracheids length difficult to measure. Helical thickenings usually absent, or rarely appear.

Axial parenchyma – in the cross sections is absent, or rarely present as dispersed thin-walled cells with dark content. In longitudinal view, the parenchyma appears as vertical rows of rectangular cells, with the horizontal wall thin and smooth or feebly nodular and with some dark remains inside.

Rays – usually thin in cross section, appear in tangential section as uniseriate, but sometimes with some biseriate storeys, or even as 2-3-seriate rays. The ray height varies from 2–32 to up to 56 cells (average height - 16 cells). The ray cells appear ovoid-rectangular, with 26–39 μm in height and 23–30 μm in width. Lateral triangular spaces are present. Their density is 6-9 rays on tangential milimeter. In radial section, the rays appear heterogeneous, because they have thicker walled cells, as ray tracheids, beside the thinner-walled parenchymal body cells, and are all procumbent. The ray cells have 8-20 μm tall, the marginals are slightly taller, of 25-30 μm. The horizontal walls of the ray cells are smooth and usually pitted, and the tangential end-walls are relatively thick, of 1.5-2 μm the simple wall and are nodular, as typical juniperoid thickenings. The ray tracheids are located in the ray-body or marginally, and have smooth or slightly rough thick walls. The indentures are missing or difficult to observe. Spiral thickenings are usually absent. The cross-fields are typical cupressoid, with 1-2-4(-6) cupressoid oculipores of 8-10 μm in diameter, usually in vertical pairs arranged, and with slit-like inclined apertures, of 2-5 μm.

Radial or axial resin canals – are absent.

Mineral inclusions – are not present

Affinities and discussion

The cupressaceous xylotomy of the 7 specimens studied here, assigned to the genus Protojuniperoxylon Eckhold , are definitely pycnoxylic and homoxylic (or tracheidoxylic – sensu Creber, 1972), having radial pitting on tracheids of mixed type, no resin canals, rare parenchyma but with nodular horizontal walls, rays exclusively uniseriate and cross-fields with 1-2(4-6) cupressoid pits with slit-like inclined apertures, arranged in 1-2 vertical pairs, or irregularly to slightly alternately and with nodular tangential end-walls of ray cells as typical juniperoid nodules (i.e. juniperoid thickenings).

We have discussed above the current status of “ Protopinaceae family” and of “Cheirlepidiaceae family” and, lastly, the proposal to be accepted as valid - the family name “ Hirmeriellaceae ” ( Harris, 1979), which is considered correct and valid to be used for the Mesozoic gymnosperms characterized by pollen of Classopollis - type, and was proposed for taxonomic conservation (see Doweld, 2020).

The genus name Protojuniperoxylon was established by Eckhold in his PhD Thesis ( Eckhold, 1921, 1922, p.491), to designate Mesozoic cupressaceous wood of Juniperus - type, described like this: “Annual rings more or less marked, tracheid pits in various transitional arrangements, ‘Abietineentüpfelung’ absent, but ‘Juniperustüpfelung’ present, no resin canals, cupressoid pits in cross-field, axial parenchyma occasionally present” ( Eckhold, 1921 fide Bodnar, 2017).

In fact, few species were described for this genus, sometimes revised, as follows:

Protojuniperoxylon maidstonense (Stopes) Eckhold, 1921 was taken as type-species, even if, initially, this wood type was described from the Cretaceous of Maidstone ( Great Britain), as a species of Cedroxylon , by Stopes (1915). It has uniseriate radial pitting on tracheids, few axial parenchyma with nodular end wall, and cupressoid cross-fields (see Bodnar and Artabe, 2007).

Protojuniperoxylon hornei (Seward and Bancroft) Eckhold, 1921 was initially described as Jurassic species of Cedroxylon and later, of Scotoxylon ( Vogellehner, 1968) , so, it could be doubtful for comparison.

However, Zhang et al. (2000) described a Scotoxylon yanqingense Zhang and Zengh , a Late Jurassic Chinese species, as representing secondary wood of Protojuniperoxylon - type, but devoid of axial parenchyma.

Protojuniperoxylon ischigualastensis ( Bonetti 1966) Bodnar and Artabe, 2007 is a Triassic wood from Argentina, which has mixed radial pitting on tracheids, cupressoid cross fields, juniperoid thickenings on the end walls of ray parenchymal cells and nodules on the horizontal walls axial parenchyma, which are typical for Juniperus wood-type.

Protojuniperoxylon arcticum Selling, 1951 described on some Mesozoic root-wood remains from Hope Island ( Svalbard, Norway) is poorly identified, for it is most probably a bennettitalean taxon ( Cycadeoidea Buckland ), showing interactions with chytrid fungi and bacteria (see Strullu-Derrien et al., 2012; McLoughlin and Strullu-Derrien. 2016).

Ruiz and Bodnar (2019) revised a Mid Triassic species of Cupressinoxylon of Bodnar et al. (2015) as Juniperoxylon zamunerae (Bodnar et al.) Ruiz and Bodnar , and made an extensive discussion on the wood structure of Juniperus - type including in a table the described species of Protojuniperoxylon together with Mesozoic and Cenozoic species of Juniperoxylon , all of them characterized by the presence of nodular ray parenchyma end-walls (i.e. ‘Juniperustüpfelung’), details also observed in our material.

Also, very useful is the discussion of Akkemik (2021), who described and identified an Early Miocene species of Juniperoxylon from Turkey, as having typical xylotomy of Juniperus type, proposing even an identification key that includes also some species of Protojuniperoxylon .

Our material displays the typical xylotomical features of Juniperus type as cupressaceous wood with mixed 1-2 seriate radial pitting on tracheids, rare or absent parenchyma, and usually uniseriate rays with cupressoid cross-fields in vertical pairs and juniperoid nodules on the tangential walls of the ray cells. Evaluating these details comparatively with those included in Table 1 from Ruiz and Bodnar (2019), and using the identification key of Akkemik (2021), we observe that our specimens are not identical to any described species. Thus, we describe a new species named here Protojuniperoxylon holbavicum sp. nov. The designated holotype is the sample 27706 (inventory number), kept in “Grădinaru Collection”, hosted by National Geological Museum, from Bucharest.

The diagnosis of the species Protojuniperoxylon holbavicum sp. nov.

Secondary tracheidoxylic wood, with thick-walled tracheids with uniseriate pitting, or even biseriate of mixed type, parenchyma absent or few and with nodular horizontal walls, heterogeneous uniseriate rays with juniperoid nodules on tangential walls or ray cells, cross-fields with 1-2(4-6) small cupressoid pits per field, as 1-2 vertical pairs pits and when more, slightly irregular or alternate, and having slit-like inclined apertures.

Figures

Fig. 2 Protojuniperoxylon holbavicum sp. nov. (inventory no. 27706). a-c: Cross section - tracheids polygonal with rounded corners, and linear rays; d-f: Tangential section - uniseriate rays with biseriate storeys with polygonal ray-cells, with lateral empty spaces; unpitted tracheids; g-j: Radial section –uniseriate radial pitting on tracheids as hexagonal pits; araucarioid cross-fields with vertical pairs of pits or slightly irregular; end-wall with juniperoid thickenings (see arrow).