Juniperoxylon acarcae Akkemik, 2020

IAMANDEI, STĂNILĂ, IAMANDEI, EUGENIA, VELITZELOS, DIMITRIOS & VELITZELOS, EVANGELOS, 2022, Palaeoxylotomical Studies In The Cenozoic Petrified Forests Of Greece. Part Two - Conifers, Acta Palaeontologica Romaniae 18 (1), pp. 65-111 : 71-73

Juniperoxylon acarcae Akkemik, 2020

Fig. 3 , a-i.

Material

The studied samples of fossil wood were collected from Greece, the Aegean area, both from continental and insular part. All of them showed a similar cupressaceous xylostructure, of Juniperus - type and were grouped under the genus Juniperoxylon . There are 13 fragments of petrified (silicified) wood and were collected from late Oligocene deposits from Evros, i.e. from Lefkimi - the samples numbered with field numbers Lfk.2, 4a, 5a, 52, 60, 72, 176, 261, 266, 282, 306 and from Sappes – the sample Spp.1077; and also, from the early Miocene of Limnos island – the sample Li.203. The studied samples are registered as “Velitzelos Collection” and stored in the Collection of the Faculty of Geology and Geoenvironment, of the NKUA.

Microscopic description

Growth rings – usually narrow, but sometimes larger, and with distinct ring-boundaries which appear often wavy in cross-section. The transition from early wood to late wood is sometimes gradual, but often abrupt. Axial resin canals not present.

Tracheids – in the early wood have polygonal rounded in cross section, (15-)26-40 / 15-22 μm the radial / tangential diameter and relatively thick walls, of 4-7 μm double wall. In the late-wood they are smaller, with diameters of 5-12 / 9-20 μm and thick walls 8-10 μm (double wall). Intercellular spaces present. Tracheid length could not be measured. On their radial walls round bordered pits are present, sometimes ornate, of 15-17 μm in diameter, uniseriate, sometimes biseriate. On the tangential walls smaller round pits of 6–7 μm diameter appear, showing round to slightly oval and obliquely oriented apertures. Helical thickenings and callitroid thickenings absent, but, sometimes, warty areas appear. Organic deposits, as resin remains, sometimes are present inside tracheids.

Axial parenchyma – is often abundant, dispersed or in short tangential rows, especially in transitional and late wood. The parenchyma transverse end walls are nodular.

Rays – exclusively uniseriate and in tangential view usually appear of low to medium height, having 1-9(-15) cells tall, sometimes more. Ray density is 6-12 rays per tangential mm. Regarding their composition, the rays are homogeneous, with cells all procumbent and ray-tracheids absent. The horizontal walls of ray cells are thick, smooth and pitted, and the tangential end-walls are inclined, distinctly pitted and with typical juniperoid nodules, beadlike. The cross-field pits are of cupressoid type, usually as 1−2(4) small pits, of 6-8 μm, with oblique slit-like apertures and in vertical or horizontal arranged. Indentures not observed or absent. The ray cells often keep resinous remains inside.

Resin canals – are absent.

Mineral inclusions – are absent.

Affinities and discussions

The cupressaceous xylotomy of the studied 13 specimens marked by the presence of ‘juniperoid nodules’, i.e. the nodular end walls of ray-cells, suggest a wood-type of Juniperus L., a genus which belong to Cupressoideae subfamily (Gadek et al., 2000; Farjon, 2001, 2005; Christenhusz et al., 2011). Here you are the essential xylotomic characters of the genus Juniperus : tracheids with exclusively uniseriate radial small pits; axial parenchyma abundant, with transverse end-walls pitted and nodular; low rays, with cupressoid cross-fields and juniperoid nodules (Greguss, 1955; Watson & Dallwitz, 2008, onwards). The xylotomy of Juniperus - type appear to be very similar to that of Cupressus - type, but ray-height and ray-frequency are different (rays smaller in height, but more numerous in Juniperus ) and mainly the end walls of ray-cells, which are typically nodular in Juniperus (as ‘juniperoid nodules’), smooth or rarely weakly nodular in Cupressus , details which can help in distinguishing between these two genera (Greguss, 1955; Schweingruber, 1990; Akkemik & Yaman, 2012; Crivellaro & Schweingruber, 2013; Román-Jordán, 2016; Román-Jordán et al., 2017).

• The genus Juniperoxylo n was created firstly by Houlbert (1910), but it was Kräusel who have imposed it by publishing the species Juniperoxylon silesiacum (Prill) Kräusel (in Prill & Kräusel, 1919). Also, Kräusel (1949) validated the genus name and wrote a short protologue for it: “Wood, similar to Cupressinoxylon . Ray cell walls, at least the terminal ones, more or less strongly pitted, so determining the 'juniperoid nodules' on the end-wall of ray cells, (‘Juniperustüpfelung’, Gothan, 1905), and traumatic wood never with resin pockets”. The type-species stated was Juniperoxylon turonense Houlbert , described from the Miocene of Touraine, France (Kłusek, 2014; Dolezych, 2016). However, this species was reconsidered by Philippe & Bamford (2009) and revised as not correctly identified, having a structure of Taxodioxylon - type, devoid of ‘Juniperustüpfelung’. But, since the original material of the type-species is lost and this genus name should be typified, the authors concluded that its use should not be recommended.

• Vaudois & Privé (1971), had revised all the Cupressaceous fossil lignotaxa published to date, and have imagined an identification key for ‘cupressaceous’ wood structures, specifying that Juniperus wood-type has “specific juniperoid nodules on the inclined tangential walls of ray-cells, in radial view”.

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• But a well documented discussion on the validity of the Juniperoxylon genus was made by Dolezych (2016), who also described a new species, Juniperoxylon schneiderianum , and discussed the validity of some European previously described species, probably ignoring the recommendation of Philippe & Bamford (2009). This species has diffuse axial parenchyma and cross-fields with cupressoid pits but also taxodioid and no indentures, so it is slightly different from our studied specimens.

• Recently, Ruiz & Bodnar (2019), revising the type material of Cupressinoxylon zamunerae described by Bodnar et al. (2015), have transferred it to Juniperoxylon , as a new combination: J. zamunerae (Bodnar et al.) Ruiz et Bodnar , taking into account the presence of juniperoid nodules on the end walls or ray-cells, the aspect of the cross-fields with vertical pairs, the scarce and diffuse axial parenchyma, and the rays tall of up to 34 cells and radial pits on the tracheids, spaced or contiguous, features partially present in our specimens as well.

• In the same paper, the authors discuss some previously described species of Juniperoxylon , reassigned in time to other taxa (Ruiz & Bodnar, 2019) and made a revision of the described species of Juniperoxylon , resulting only 9 species that can be considered correctly identified. However, since Philippe & Bamford (2009) have infirmed the identification of J. turonense Houlbert , there are only 8 valid species left, which we add to the species recently described by Akkemik (2020a).

• Similar fossil wood remains were described by Akkemik et al. (2016), and by Acarca-Bayam et al. (2018) from central Anatolia, as wood of Juniperus type and, more recently, a new species named Juniperoxylon acarcae was described by Akkemik (2020a), a form closes to the current Mediterranean forms, and which presents a xylotomical details very similar to those of the here studied specimens.

Thus, our studied specinmens present a typical xylotomy of Juniperus , as described by Greguss (1955), Vaudois & Privé (1971), Dolezych (2016) and Ruiz & Bodnar (2019). According to the two comparative tables of Ruiz & Bodnar (2019), including the description and discussion accompanying the recent new species described by Akkemik (2020a), a species which has many similarities with our specimens regarding the tracheidal pitting, the axial parenchyma, the pits from cross-fields, we attribute the studied specimens to the species Juniperoxylon acarcae Akkemik, 2020 .

The xylotomical details are also very similar to the extant species of the junipers characteristic to Eastern Mediterranean (Aegean) area, as Juniperus macrocarpa Sibth. et Sm. , J. drupacea Labill. , J. excelsa M.Bieb. , J. communis L. or J. phoenicea L., as Asensi Amorós (2016) cite also from the current Egyptian indigenous flora, also present in Sinai.

According with Farjon (2001, 2005), Adams (2004, 2007) and Mao et al. (2010), Juniperus is a genus that has numerous species distributed almost all around the world, but especially in the Northern Hemisphere, as a result of the Oligocene – Miocene diversification and migration in Eurasia and North America, related to climate evolution. Some of Juniperus species appear distributed in Europe and Mediterranean Sea, including also the Canary Islands, Azores, Northern Africa and Asia Minor, and have migrated as far as the Arabian Peninsula and the “Afromontane zones” of Eastern Africa, like Juniperus procera Hochst. ex Endl. ( Mao et al., 2010, Fig. 1,5,6).

Figures

Fig. 3 a-i. (graphic scale). Juniperoxylon acarcae Akkemik, 2020. (Specimen Lfk.266). a–c: Cross section - transition abrupt, distinct growth rings; parenchyma few, diffuse; rays uniseriate; d–f: Tangential section - pitting on tracheids absent; nodular parenchyma end walls (arrow); rays uniseriate; g–i: Radial section - tracheidal pitting uniseriate; rays homocellular, cells all procumbent, marginals taller; tangential end-walls with juniperoid nodules (inclined arrow); poorly preserved cross fields with 1-2 cupressoid pits, usually arranged as vertical pairs pits (horizontal arrow).