Pterocaryoxylon sp.

Wheeler, Elisabeth A. & Manchester, Steven R., 2021, A Diverse Assemblage Of Late Eocene Woods From Oregon, Western Usa, Fossil Imprint 77 (2), pp. 299-329 : 315-316

Pterocaryoxylon sp.

Text-fig. 8a–f

M a t e r i a l. UF 279-24551 (minimum estimated diameter 11.8 cm), UF 279-24557 (minimum estimated diameter 13 cm), UF 279-85024.

D e s c r i p t i o n. Growth rings present, marked by radially flattened fibers and differences in latewood and earlywood vessel diameters of successive growth rings ( Text-fig. 8a, b ). Semi-ring-porous.

Vessels solitary and in radial multiples of 2, average tangential diameter of earlywood 206 (28) µm, range 124–294 µm; perforations simple, intervessel pits alternate ( Text-fig. 8c ), ca. 7 µm; vessel-parenchyma pits similar to intervessel pits ( Text-fig. 8d ); vessel element lengths averages 460 (73)–486 (88) µm; thin-walled tyloses occasional.

Fibers non-septate, thin-walled, pits not observed.

Axial parenchyma scanty paratracheal to vasicentric, marginal, and in tangential bands one to two cells wide throughout the growth ring, lines more closely spaced in the latewood than in the earlywood ( Text-fig. 8a, b ); strands usually of eight cells.

Rays 1–3(4)-seriate ( Text-fig. 8e ). Multiseriate rays heterocellular, with procumbent body cells and usually with 1–2 marginal rows of square to upright cells; uniseriate rays composed of mostly upright cells ( Text-fig. 8f ), total multiseriate ray height averages 382 (91) µm, range 225– 625 µm. 10–12/mm.

Crystals not observed. Storied structure absent.

R e m a r k s. These juglandaceous woods were compressed and contorted, especially their earlywood. For measuring vessel diameters, we selected vessels that were oval to circular in outline and that we considered to be close to their original outline in the living tree.

C o m p a r i s o n s w i t h e x t a n t w o o d s.Affinities with Juglandaceae are indicated by the combination of semiring-porosity, vessels solitary and in short radial multiples, narrow continuous lines of axial parenchyma, medium-sized alternate intervessel pits, vessel-ray parenchyma pits similar in size to intervessel pits. Because these woods have exclusively simple perforations and lack crystals, they are most similar to Pterocarya KUNTH and the butternut group of Juglans L. (Asian species of Section Cardiocaryon, and the American J. cinerea L., traditionally placed in section Trachycaryon ). Phylogenetic analyses confirm a close relationship between Pterocarya and Juglans ( Stanford et al. 2000, Manos et al. 2007). Sometimes Pterocarya woods can be distinguished from the butternuts because latewood vessels in Pterocarya can be in a pronounced diagonal pattern ( Müller-Stoll and Mädel 1960, Miller 1976, Wheeler et al. 1978). A difference between these Post Hammer woods and woods of extant Pterocarya and the Juglans butternut group is that rays in the recent woods typically are homocellular with all procumbent cells. However, some extant juglandaceous species have heterocellular rays (e.g., Juglans californica S.WATSON of section Rhysocaryon, BWCw 8695).

C o m p a r i s o n s w i t h f o s s i l w o o d s. Because of the similarity of woods of Pterocarya and the butternut group of Juglans, Müller-Stoll and Mädel (1960) created the genus Pterocaryoxylon . One species is known from North America; Pterocaryoxylon knowltonii E.A.WHEELER, R.A.SCOTT et BARGH. ( Wheeler et al. 1978) from the early middle Eocene of Yellowstone National Park, Wyoming. Table 3 compares this older species to the Post Hammer Pterocaryoxylon and shows the latter differ in having smaller intervessel pits and taller rays. Growth rings of the Post Pterocaryoxylon are narrower than those of the Yellowstone wood. When growth rings are narrow, latewood vessel arrangement patterns may not be obvious ( IAWA Committee 1989). It is possible that if this Post wood had wider growth rings, a diagonal latewood vessel arrangement would have been observed. We are hesitant to create a new species based on differences in quantitative features and are choosing to refer to these Post Hammer woods as Pterocaryoxylon sp. The Yellowstone Pterocaryoxylon also has heterocellular rays. These western North America Pterocaryoxylon are the oldest known species of the genus. Pterocaryoxylon and Pterocarya have been reported from the Miocene-Pliocene of central and eastern Asia (e.g., Rajput and Khan 1982, Choi et al. 2010, Cheng et al. 2018), and Europe (e.g., MüllerStoll and Mädel 1960, Privé 1974, Dupéron 1988). MüllerStoll and Mädel (1960) cited another character of the type species of Pterocaryoxylon , not strictly a wood character, but useful to confirm affinity with the Pterocarya-Juglans- Cyclocarya group and distinguishing it from all other extant genera of the Juglandaceae : septate pith. The center of the stem is not known for these Eocene species.

The two juglandaceous woods of the nearby older middle Eocene Nut Beds , Oregon , differ: Clarnoxylon blanchardii MANCHESTER et E. A.WHEELER (which has solid pith rather than septate) has prismatic crystals commonly occurring in enlarged ray parenchyma cells; Engelhardioxylon nutbedensis MANCHESTER has both simple and scalariform perforation plates and prismatic crystals in ray parenchyma ( Wheeler and Manchester 2002).

C o - o c c u r r i n g f r u i t s / s e e d s. The bi-winged fruits of Pterocarya have not been confirmed prior to the Oligocene. However, the extinct 4-winged genus Cruciptera known from the middle to late Eocene of Oregon ( Manchester 1991), the early middle Eocene of Yellowstone (pers. obs.), and middle Eocene of Germany ( Manchester et al. 1994), seems to have been rather common. We speculate that Cruciptera may have been produced on trees with wood similar to that of Pterocarya , and it may have corresponded to Pterocaryoxylon .

Figures

Text-fig. 8. Pterocaryoxylon sp., a–c, e: UF 279-85024; d, f: UF 279-24551. a, b: Wood semi-ring-porous, vessels solitary and in short radial multiples, axial parenchyma scanty vasicentric, marginal, and in narrow lines, TS. c: Crowded alternate intervessel pitting, simple perforation plate (PP), TLS. d: Vessel-axial parenchyma pitting similar to intervessel pitting, RLS. e: Rays mostly 1–3 cells wide, occasionally 4 cells, uniseriate rays probably mostly square to upright cells, TLS. f: Rays heterocellular, body cells procumbent. Scale bars: 200 µm in a, b; 100 µm in e, f; 50 µm in c; 20 µm in d.