Bucklandia sp. B

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 : 41-43

Bucklandia sp. B

Fig. 8 , a-i.

Material

The studied material is represented by three small (centimetric) samples of silicified wood, collected from around Holbav locality area, on Maiului brook. These samples have the field-numbers: 1037, 1038 and 1079, in "Grădinaru Collection" and are stored now at the National Museum of Geology , in Bucharest, under the inventory numbers 27676, 27677 and 27683 .

Microscopic description

Cross-sections of the studied specimens show a wood structure of gymnospermous type ( Fig. 8a ), with some details indicative of a cycadeoid stem structure, due to the presence of idioblasts and mucilaginous canals ( Fig. 8c, h ); the xylotomical description is appropriate, in order to identify the unknown structure.

The pith – is not present in our sections because the axial part of the stem is absent in our fragmentary samples.

The cylindrical vascular system – in cross section, appears to consist of some alternate growth rings of secondary xylem and phloem, which indicate a polyxylic structure, traversed by numerous thin secondary rays ( Fig. 8a ). The wide multiseriate primary medullary rays appear only locally, in contact with the xylem of growth ring (see Fig. 8b ). Through the xylem and phloem cells, obvious idioblasts appear, carrying mucilages or crystals often grouped as druses ( Fig. 8 d-f). The cambium cells are difficult to recognize. The xylem has rectangular to square tracheids (ra/tg diameters of 18-50/20-45 μm), with rounded corners, with often slightly wavy walls, 3-6 μm as a double wall. On the radial walls, the tracheids show uni- to biseriate bordered pits, rounded or hexagonal, of 6-8 μm, with round to elliptic apertures and are contiguous and flattened ( Fig. 8i ), usually alternate, where they are biseriate. Perforations were not seen. The tangential walls are not pitted. The phloem appears as parenchymal cells, with secretory idioblasts and sclerenchymal cells often with large crystals, or druses ( Fig. 8 d-e). At the border with the pith area, mucilaginous canals appear, lined by rows of epithelial cells.

The rays – in cross- and tangential sections the secondary rays appear numerous and thin, giving a manoxylic appearance to the structure. The primary rays were not observed; but they do appear in cross-section, in contact with xylem (see Fig. 8b ). The secondary rays are usually uniseriate, very numerous and are composed of parenchymal cells, and few secretory idioblasts, so that the rays are heterogeneous ( Fig. 8g ). The ray cells have rounded to rectangular outlines, the idioblasts are similar, or slightly elongate and, in radial view, are all procumbent. The cross-fields show 2-6 oculipores, in one or two superposed rows and are slightly alternately arranged.

Axial canals - appear at the border with the pith area, as large mucilaginous canals, with diameters of 360-930 μm, lined by secretory epithelial cells ( Fig. 8c, h ).

Afinities and discussion

Having a cycadeoid stem structure, indicated by the presence of idioblasts with druses and of mucilaginous canals, we searched also for other xylotomical details, but the absence of scalariform thickenings on tracheids makes it different from the above-described form, and indicated a resemblance to a type close to the current Cycas (see Greguss, 1968).

In the Early Jurassic flora from Holbav, species of Nilssonia , Paracycas , Ctenis , Ptilophyllum , Pterophyllum appear, in addition to forms of Zamites- group (see Dragastan and Popa, 1997; Popa, 1997, 1998, 2000a, b).

Comparing to wood description of Zamuneria amyla (see Martinez et al., 2017) and, also, their identification key, we observed that our studied specimens indicate a columnar polyxylic stem, with several growth rings in the cylindrical vascular system, and with idioblasts and mucilaginous canals, similar to the genus Bucklandia Bosse, 1953 , which is a stem of Williamsonia Caruthers , as it was described by Stockey and Rothwell (2003).

Our specimens have a structure similar to a Jurassic stem described by Zhang et al. (2012) as Sinocycadoxylon , which is also characterized by a polyxylic vascular cylinder with centrifugal rings of secondary xylem and araucarioid radial pitting on the tracheids.

Also, Iamandei et al. (2003) studied a fragmentary fossil wood from the Upper Jurassic of Hăghimaş Mts., Eastern Carpathians, which is identified as Cycadoxylon sp. , which has a xylotomy very similar to our studied specimens.

Thus, the studied specimens show details that indicate a columnar form of Cycas - type (see Greguss, 1968), as is discussed above, so we assign them to Bucklandia sp. B , clearly different from the form described above.

Figures

Fig. 8 Bucklandia sp. B - inventory no. 27676 and 27677 (field no. 1037 a-f, 1038g-i). a-f: Cross section – b: - tracheids polygonal with rounded corners, and linear rays; primary ray in contact with xylem; c: - mucilaginous canals lined by secretory epithelial cells; d-e: - phloem cells with idioblasts bearing mucillages; f: - or crystals (f); g: Tangential section - uniseriate rays with biseriate storeys with polygonal ray-cells; unpitted tracheids; h-i: Radial section – mucilaginous canal (h); araucarian radial pitting on tracheids with uniseriate hexagonal pits (i), cross-fields with 2-3 superposed rows of hexagonal pits (h-i).