Pinaceae, SPRENG. ex F. RUDOLPHI, 1830

Martinetto, Edoardo, Bertini, Adele, Mantzouka, Dimitra, Natalicchio, Marcello, Niccolini, Gabriele & Kovar-Eder, Johanna, 2022, Remains Of A Subtropical Humid Forest In A Messinian Evaporitebearing Succession At Govone, Northwestern Italy - Preliminary Results, Fossil Imprint 78 (1), pp. 157-188 : 168-169

Pinaceae gen. et sp. indet.

Text-fig. 6c–f

M a t e r i a l. Fossil wood specimen MGPT-PU141107, in part permineralized, collected by P. Damarco (Repository: MGPT-PU), small part of MGPT-PU141107 specimen and 3 slides. The sampling place was indicated in the area where the plant-rich bed GLA19 crops out. The presence of permineralized wood within this bed was recently verified by the first author.

M a c r o s c o p i c d e s c r i p t i o n. The slides come from a permineralized wood fragment of very variable greyish color; approximate dimensions in cm: 15 × 10 × 5.

M i c r o s c o p i c d e s c r i p t i o n. Transverse section: Distinct growth ring boundaries, axial tracheids of polygonal section. Axial parenchyma observed. Large, thick-walled axial resin canal (normal or traumatic?) with more than 9 epithelial cells observed.

Axial resin canal diameter>60 μm. Intercellular spaces observed. Tangential section: Rays 1–10 cells high, uniseriate, partly bi-seriate. Intercellular spaces observed.

Radial section: Absence of ray tracheids, bordered pits (tracheid pitting in radial walls) not observed, cross field pits not observed, smooth (and possibly pitted) horizontal walls of ray parenchyma. Spiral thickenings observed.

B o t a n i c a l a f f i n i t i e s. The observation of resin canals in transverse section is of taxonomic importance. According to Esteban et al. (2004), this type of axial thickwalled resin canal with a diameter>60 μm and more than 9 epithelial cells can be found in Pinus caribaea MORELET , Picea orientalis (L.) PETERM., Picea likiangensis (FRANCH.) E.PRITZ. , Larix occidentalis NUTT. (also in Keteleeria CARRIÈRE , although the size of the resin canals does not match with the ones referred to this genus, but this difference in size could be also assigned to ecological/environmental conditions). If the occurrence of the resin canals were of traumatic origin, the taxonomic selection would be wider, including also Abies MILL. , Tsuga (ENDL.) CARRIÈRE and Sequoia sempervirens ENDL. ( IAWA Committee 2004) .

R e m a r k s. In coniferous woods, three types of axial parenchyma are found (a) marginal, (b) fusiform ( Noshiro and Fujii 1994) and (c) the one related to the epithelial cells surrounding the resin canals ( Hacke et al. 2015), as discussed also in Dolezych et al. (2021). Kuroda (1986) refers to the epithelial cells as “septated cells”, while the term used for the same character in Mesozoic fossil woods is “septate tracheids” (e.g., Philippe 1993, Iamandei et al. 2005). Lin et al. (2002) described the structure of resin canals, stating that the epithelium surrounding the canals consists of parenchyma cells, and that the outer parenchyma cells surrounding the epithelium can be partly parenchymatous and partly tracheary or completely tracheary with septa and small pits. The marginal parenchyma (sensu Noshiro and Fujii 1994) associated with the (traumatic and normal) axial resin canals is named “subsidiary parenchyma cells” by Wiedenhoeft and Miller (2002), which is followed by Esteban et al. (2005). Unfortunately, the descriptions of the fossil record regarding the axial parenchyma are limited to its existence and not on the detailed identification of the axial parenchyma type (or types). The identification of the type of the axial parenchyma can help to distinguish genera within Pinaceae ( Noshiro and Fujii 1994) .

The occurrence of spiral thickenings, roundish tracheids and partly biseriate rays may be related either to specific genera or to compression wood sensu Timell (1986). The occurrence of relatively large resin canals is also observed in compression wood as in our MGPT-PU141107 sample but could be also of taxonomic importance. Ecological disruptions by biotic, e.g., aphid infection and/or fungi, and abiotic factors can cause the above-discussed abnormalities ( Timell 1986), as well as the occurrence of intercellular spaces (or interstitial spaces sensu Bolton et al. 1975), which were also observed in this sample. The observed abnormal discoloration (white and black) could be related to wood shrinkage caused by several factors discussed in Rössler et al. (2021), among which are the mineralization and the decay caused by bacteria and fungi. The latter case is presented also in Wei et al. (2019) and Morris et al. (2021). The specific reason of the discoloration of our specimen remains open.

Figures

Text-fig. 6. Transmitted light microphotographs of permineralized wood from Govone. a, b: cf. Cupressinoxylon sp., radial section, MGPT-PU141105, a – nodular end of ray parenchyma (arrow), b – thick and pitted horizontal walls of ray parenchyma (arrow). c–f: Pinaceae gen. et sp. indet., MGPT-PU141107, c – abnormal discoloration due to ecological disruptions (radial section), d – rays up to 10 cells high, uniseriate, partly biseriate (black arrow), intercellular spaces observed (white arrows) (tangential section), e – large, thick-walled axial resin canal with more than 9 epithelial cells observed, axial resin canal diameter>60 Μm (transverse section), f – spiral thickenings due to compression (white arrow) (radial section).