Acer Post Hammer sp. 2

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 : 322

Acer Post Hammer sp. 2

Text-fig. 11f–i

M a t e r i a l. UF 279-34466.

D e s c r i p t i o n. Growth rings distinct, marked by radially flattened fibers. Diffuse-porous ( Text-fig. 11f ). Vessels solitary (48 %) and in radial multiples of 2–4; average tangential diameter 55 (11), range 39–73 µm; vessel frequency 64–78/mm 2; perforations simple; intervessel pits crowded alternate ( Text-fig. 11g ), rounded to polygonal in outline with included apertures, 8–10 µm; vessel-ray parenchyma pits similar in size and shape to intervessel pits; helical thickenings present along entire length of the vessel element; ( Text-fig. 11g ) vessel element lengths 275–495 µm; mean 390 µm (n = 12); tyloses absent. Fibers non-septate, walls of thin to medium thickness, pitting not observed.Axial parenchyma marginal ( Text-fig. 11f ), apparently diffuse; strands of chambered crystalliferous cells with more than 16 chambers per strand ( Text-fig.11i ); one crystal per chamber. Rays 1–4(–5)-seriate ( Text-fig. 11h ). Multiseriate rays homocellular, composed of procumbent cells; multiseriate ray height averages 512 (206) µm, range 175–850 µm; 5–7/mm. Chambered crystalliferous cells, occasional, more than 16 chambers per strand; one crystal per chamber. Storied structure absent.

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. Woods of Acer are relatively easy to identify to genus because of their distinctive combination of features: diffuse-porosity (5p), vessels solitary and in short radial multiples (6a 7a 8a 9a 10a 11a), exclusively simple perforation plates (13p 14a), alternate intervessel pits that are neither minute nor large (22p 24a 27a), vessel-ray parenchyma pits similar in size and shape to the intervessel pits (30p), spiral thickenings throughout the vessel elements (36p 37p), vessels not wide or few (42a 43a 46a), non-septate fibers with simple to minutely bordered pits (61p 65a 66p), non-storied homocellular rays that are not exclusively uniseriate or>10-seriate (96a 99a 104p 118a), axial parenchyma not abundant and marginal parenchyma present (77a 79a 80a 83a 86a 89p) and in some species crystals in chambered axial parenchyma cells (e.g., Brazier and Franklin 1961, Panshin and DeZeeuw 1980).

Dipteronia OLIV. wood differs from Acer wood in that helical thickenings are uncommon and faint in the narrower vessel elements; it also differs from these Post maple woods as its rays are wider (to 6-seriate) and commonly> 1 mm high (T. Itoh, personal communication).

Today there are ~125 Acer species ( Mabberley 2017). It is not easy to identify an isolated piece of maple wood of unknown geographic origin to a species or section. In Ogata’s (1967) monograph of the genus, he suggested ray shape, ray width in cell number, and crystal occurrence are useful for distinguishing sections in Acer . Based on these features we recognize two species of Acer in the UF 279 assemblage.

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. The oldest known wood with features unique to Acer occurs in the middle Eocene Clarno Nut Beds ( Wheeler and Manchester 2002). Takahashi and Suzuki (1988) reviewed the record for fossil Acer woods. More recently, fossil Acer woods have been reported from Asia ( Jeong et al. 2009) and Turkey ( Akkemik et al. 2016, 2018, Bayam et al. 2018). Table 5 compares their features; this table only includes reports for stem wood with reasonably complete anatomical descriptions and images. The Turkish Miocene woods are distinct from all other Acer fossil woods because of their markedly higher vessel frequency. Acer PH sp. 1 , which lacks crystals, is similar to A. minokamoensis E.K.JEONG, KYUNG.KIM et MITS.SUZUKI in vessel diameter and ray size, but its description only notes that the vessels are numerous. Thus, it is not clear whether or not they are similar in vessel frequency. Acer PH sp. 2 differs from other crystal-bearing fossil Acer woods in vessel frequency and ray height. We are hesitant to provide diagnoses that rely heavily on differences in quantitative features for distinguishing species.

Co-occurring fruits / seeds or leaves. Wolfe and Tanai (1987) described seven species of Acer based on leaf and fruit remains from the Teater Road locality, which they referred to as Sheep Rock Creek. Dipteronia fruits are also recognized there ( McClain and Manchester 2001).

Figures

Text-fig. 11. Acer Post Hammer species 1, UF 279-34456. a, b: Diffuse-porous wood with distinct growth rings, marked by marginal parenchyma, vessels solitary and in short radial multiples, TS. c: Crowded alternate intervessel pits, TLS. d: Simple perforation plates, helical thickenings in vessel elements, TLS. e: Rays 2–3-seriate, gum deposit in vessel element, TLS. Acer Post Hammer species 2. UF279-34466. f: Diffuse-porous wood with distinct growth rings, marked by marginal parenchyma, vessels solitary and in short radial multiples, TS. g: Alternate intervessel pits, helical thickenings in vessel elements, TLS. h: Rays 1–4(–5)-seriate, TLS. i: Crystalliferous strand, multiseriate ray, TLS. Trochodendron beckii, UF 279-24558. j, k: Distinct growth rings, abrupt transition from earlywood to latewood, vesselless, wide raysnoded atgrowth ring boundaries, TS. l:Rays of two distinct sizes, uniseriate and multiseriates>10-seriate, TLS. m. Scalariform intertracheary pits. RLS. Scale bars: 500 µm in j; 200 µm in a, f, k, l; 100 µm in b, h; 50 µm in c, d, e, g, i, m.