Bucklandia sp. A

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 : 37-41

Bucklandia sp. A .

Fig. 6 , a-i; Fig. 7 , a-i.

Material

The studied material is represented by a piece of silicified wood collected from Holbav area, on Maiului brook. This specimen has the field-number 1107, in "Grădinaru Collection", and is stored now at the National Museum of Geology in Bucharest, under the inventory number 27719 .

Microscopic description

In cross-section, the structure of the wood is of gymnospermous type, and some details (such as the presence of the typical idioblasts and axial mucilaginous canals) suggest a cycadeoid polyxylic stem structure, which is also supported by the presence of scalariform thickenings of Zamia type on the tracheids in vertical view ( Greguss, 1968), so, the xylotomic description will be adequate: Pith – unfortunately, is absent in our fragmentary samples which does not retain the axial part of the stem, so we did not have the possibility to describe its component elements (as parenchyma cells, idioblasts, medullary vascular bundles and mucilaginous canals).

Cylindrical vascular system – in cross section, is represented by some alternative growth rings of secondary xylem and phloem (not as annual rings) and numerous thin secondary rays, so giving a polyxylic structure ( Fig. 6a ), crossed by wide multiseriate primary medullary rays which connect the axial pith with the cortex (but this aspect does not appear in our sections). The cambial cells are recognized with difficulty, since they are very similar to the neighboring cells. The xylem has rectangular or square tracheids, in gradual transition from early- to the late-wood, with r/tg diameter of 25-65 / 10-15-30 μm, with relatively thick walls, of 4-8 μm the double wall, ( Fig. 6 a-f). Their walls are often corrugated, by compression. On the radial walls, the tracheids show uni- to biseriate bordered pits, rounded to hexagonal, contiguous and flattened, sometimes alternate, when biseriate ( Fig. 7g , arrow). The pits have diameters of 9-12 /8-15 μm, with round to elliptical apertures. Very obvious are the scalariform thickenings of Zamia type, which are often connected by inclined bars, giving a reticular appearance ( Fig. 7 a-e). No perforations were observed. The tangential walls are not pitted ( Fig. 6 g-i). The phloem has parenchymal cells, (unclear if they are sieve cells), thick-walled fibres, secretory idioblasts, and sclerenchymal cells ( Fig. 6 d-e).

Rays – in transversal and tangential sections, the primary rays were not observed in our fragmentary material, but numerous secondary rays appear, giving a manoxylic aspect to the structure. They are uniseriate, sometimes 2(- 3)-seriate, of low to mid tall, and are composed of parenchyma cells and few secretory idioblasts, so they are heterogeneous. The ray cells are rounded to rectangular in outline, the idioblasts are similar or are slightly elongate and, in radial view, appear all procumbent. In cross-fields they have 2-6(9) oculipores usually in two superposed rows arranged ( Fig. 7 d-i).

Cortex – is not present in our sample, so parenchymal cells, idioblasts, mucilage canals and leaf traces, were not observed.

Afinities and discussion

Evaluating the general image of the wood structure in cross section, we noticed some details that indicated a possible cycadeoid stem-structure of polyxylic type, by the presence of idioblasts and mucilaginous canals. Thus, we searched for more xylotomical details in order to identify the unknown structure.

As is known, the Cycadeoidophyta is a Mesozoic extinct taxon, which include two families: Cycadeoidaceae Buck. (or Bennettitaceae Engl. ) – with the genera Cycadeoidea Buck. (or Bennettites Caruthers ) and Monanthesia Wieland ; they have a barrel-shaped trunk, like a large pineapple, with a crown of leaves; the second family, Williamsoniaceae (Carruthers) Nathorst - with Williamsonia Caruthers as type genus, a form with a columnar trunk with frond like leaves at branch tips (see Stockey and Rothwell, 2003). This family includes a lot of described genera of plant-parts, variably named, which send sometimes to a current Cycadalean genus, as follows: Williamsoniella , Nilssoniopteris , Bennettitanthus , Cycadocephalus , Fredlindia , Ischnophyton , Lyssoxylon , Serenopsis , Weltrichia , Zamites , Anomozamites , Otozamites , Podozamites, Ceratozamites , Banatozamites , Pterophyllum, Wielandella, Crossozamia, Dioonites, Eostangeria, Palaeocycas, Pseudoctenis, Ticoa , and many others (see Taylor et al., 2009; Martínez et al., 2012, 2017). Numerous fossil remains of Bennettitales were described from Romania. Thus, in the Holbav-Cristian-Vulcan-Codlea area Givulescu (1991) cited an Early Jurassic flora (or “Liasic flora”) with the presence of Zamites , Nilssoniopteris and Pterophyllum (from Bennettitales ) and Phoenicopsis ( Ginkgoaceae ). In recent decades, Dragastan and Popa (1997), Popa (1997 a, 1998, 2000a,b), and Popa and van Konijnenburg-van Cittert (1999, 2006) contributed more to the Early Jurassic flora in the Holbav area, describing Nilssonia cf. undulata , Paracycas sp. , Ctenis grandifolia ( Cycadales ) and Ptilophyllum rigidum , Pterophyllum magoti , P. neagui (as Bennettitales ) and beside them - Taeniopteris sp. ( Ginkgoales ), Phoenicopsis potoniei (Czekanowkiales) and Geinitzia sp. (Conifers). Also, from the Cristian area were described Pachypteris grădinarui , Otozamites mandelslohi , O. molinianus and a Desmiophyllum sp. which belongs, probably, to Czekanowskiales. Also, Dragastan and Popa (1997) and Czier (2016b) advanced some phytostratigraphic schemes based on the Early Jurassic foliar material identified in the Holbav area.

However, there are few genera described in the world from the study of fossil stem remains, often with local importance and with names related to the original fossiliferous site or people (see list in Martínez et al., 2012, 2017; Zhang et al., 2012). For example, Martinez et al. (2017), have described a well-preserved Jurassic bennettitalean specimen from Patagonia, as Zamuneria amyla Martínez, Iglesias and Artabe, and made a carefully documented comparison with the xylotomy of the extant cycadalean genera and also, with all Mesozoic Bennettitalean genera.

The studied specimens show a cycadeoid polyxylic structure with scalariform thickenings on tracheids which indicate similarities with stem of Bucklandia type (see Bosse, 1953; Sharma, 1967, 1969, 1973, 1991; Saiki and Yoshida, 1999) or even with Sahnioxylon (see in Philippe et al. 1999) - the latter being considered “nomen ilegitimum” (see IFPNI - www.fossilplants.info/genus.htm?id= D46FC51A-7AEB-421E-AF52-1A3F90515E43).

Because the structure of our specimen indicates a columnar polyxylic stem, the sample does not preserve the pith from the central part of the stem and also the cortical zone, both of parenchymal tissue, which were likely easily destroyed during the early stages of fossilization. We cannot see typical parenchymal cells, idioblasts, medullary vascular bundles, mucilaginous canals, and transfusion cells or leaf bases, in the cortex.

However, the polyxylic cycadeoid structure with idioblasts and scalariform thickenings on tracheids, that resemble those in the current Zamia , Ceratozamia (see Greguss, 1968) and are partially similar to the structure of the Jurassic genera Bucklandia Brongniart, Zamuneria Martínez, Iglesias and Artabe and Lioxylon Sharma (see Martínez et al., 2017), which are also characterized by polyxylic stem with centripetal and centrifugal vascular systems and by the presence of numerous idioblasts in the structure.

In the studied Mesozoic areas of Romanian Carpathians, many fossil macro-remains have been described and attributed especially to taxa from Zamites group: Anomozamites , Otozamites , Podozamites, Ceratozamites , Banatozamites (see Givulescu, 1991; Dragastan and Popa, 1997; Popa, 1997, 1998, 2000b; Popa and van Konijnenburg-van Cittert, 1999, 2006; Czier, 1999, 2001, 2008, 2009, 2016a,c, 2018), and such taxa have also been commonly described in Europe (see Barbacka et al., 2014). Thus, from the Lower Jurassic of Anina, Banat region, Romania, Czier (2009) described two Bennettitalean species: Banatozamites calvus Czier , by the study of leaf impresions and Bucklandia aninaensis Czier , by the study of a small stem with petioles, interpreted to belong to the same plant; they have fine longitudinal ridges, and rows of rectangular to rounded-elongated cells.

The specimen studied here has details that resemble a Zamia - type structure (see above), especially due to presence of scalariform thickenings on tracheids, even with reticular appearance (see Greguss, 1968). Also due to the presence of idioblasts and mucillaginous canals, we assign it to Bucklandia sp. A , probably representing wood of an extinct form from the Zamites group, commonly present in the Romanian Carpathians (see above).

Regarding the genus Bucklandia , erected by Brongniart (1828), we consider it as a still valid genus, because it was proposed by Doweld (2012) to be conserved. However, Herbst and Crisafulli (2016) ignoring this proposal, described a new genus, Buckya Herbst and Crisafulli, to replace the old genus Bucklandia Brongniart , recommending transfer of all the species previously described to the new proposed genus, as nov. comb. (see Herbst and Crisafulli, 2016, p. 97-98).

But, we observed that there is another possible problem of this name, Buckya, which could become illegitimate, since there are two quasi-homonyms: Buckia Cobos, 1956 , which is the name of a current insect from the Order Coleoptera L., and Buckia Rios, Gallego and Guerra , (see in GBIF-online), but is also used to describe a moss, a homotypic synonym for Hypnum Hedw. (Order Hypnales Buck. and Vitt. ).

Figures

Fig. 6 Buckladia sp. A. - inventory no. 27719 (field no. 1107). a-f: Cross section - gymnosperm structure with tracheids rectangular with rounded corners, thin curled walls in the early-wood, thick walled in the late-wood; idioblasts between tracheids; d-e: Numerous secondary rays; g-i: Tangential section - unpitted tracheids; uniseriate rays.

Fig. 7 Buckladia sp. A - inventory no. 27719 (field no. 1107). a-i: Radial section - d-g: - scalariform thickenings of Zamia type on tracheids, with reticular aspect; g-i: - araucarioid cross-fields with alternate in 2-3 superposed rows.