Styphnolobium, SCHOTT, 1830

Wheeler, Elisabeth A., Manchester, Steven R. & Baas, Pieter, 2023, A late Eocene wood assemblage from the Crooked River Basin, Oregon, USA, PaleoBios 40 (14), pp. 1-55 : 13-15

STYPHNOLOBIUM SCHOTT, 1830 CF. STYPHONOLOBIUM SP.

FIG. 7A–I

Descriptio n — Growth rings distinct. Wood ring-porous. Earlywood vessels mostly solitary, rarely in radial multiples of two ( Fig. 7A–C ), average tangential diameter 99 (SD=21) µm, range 56–134 µm, earlywood zone 2–3 vessels deep with an abrupt transition to latewood with vessels solitary and in short radial multiples ( Fig. 7A ); perforation plates simple ( Fig. 7D, H ); intervessel pitting crowded alternate, polygonal in outline ( Fig. 7D ), 6–8.5 µm in horizontal diameter; vessel-ray parenchyma pits similar to intervessel pits ( Fig. 7E ); vessel elements short, average 213 µm (SD=53, n=7).

Fibers non-septate, pits not observed ( Fig. 7F, G ).

Axial parenchyma aliform-confluent-banded ( Fig 7A, C ); strands of 2–4 cells; non-storied. ( Fig. 7F, G ).

Rays 1–4 (-5)-seriate, heterocellular ( Fig. 7F–H ), in tangential view cells appear isodiametric and angular in outline, ray heights average 195 µm (SD=66), range 104–313 µm.; 5–8 per mm; non-storied.

Specimen— UF 278-84867, estimated maximum diameter 2.5 cm.

Occurrence— Dietz Hill (UF 278).

Comments— Rays near the pith had more upright cells than did the rays farther away. We are not sure what the ray cellular composition of an older stem would be, although the tangential section taken at the periphery suggests they will become homocellular and/or heterocellular with a single marginal row of square cells. This sample contained insect frass and invading roots and had a total of 16 growth rings. Also, in such a narrow stem, vessel diameters probably are narrower than would characterize mature wood of this wood type. We did not observe helical thickenings in this sample, which is unusual for ring-porous legume woods.

Comparisons to extant woods— One of our searches used 1p 3p (ring-porous wood), 7a 8a 9a 10a 11a (vessels randomly distributed, solitary and in short radial multiples), 13p 14a (perforation plates exclusively simple), 22p 26p (medium-sized alternate intervessel pitting), 30p (vessel-ray parenchyma pitting similar to intervessel pitting), 61p 66p (non-septate fibers with simple pits), 83p 85p (axial parenchyma confluent and in bands), 98p 105a (maximum ray width 4–10-seriate, and not composed exclusively of square/upright cells). This particular search only returned Styphnolobium affine (Torr. and A. Gray) Walp. (1842) (synonym Sophora affinis Torr. and A. Gray, 1840 ). The other searches we did, which were variations on the search given above, returned more legumes, as well as Paulownia Siebold and Zucc. (1835) and some Lamiaceae Mart. (1820) , but invariably included Styphnolobium Schott (1830) in the results. This fossil has features in common with the Sophora A group of Fujii et al. (1994, Table 1 ), which includes S. affine . Gasson's 1994 review of the anatomy of the Sophoreae Spreng and DC. (1825) also indicates this fossil has a similarity with Stypholobium.

The LPWG (2017) proposed a new classification of the Fabaceae replacing the three traditional subfamilies: Caesalpinioideae DC. (1825), Mimosoideae DC. (1825), and Papilionoideae DC. (1825), which were based on floral characters, with six subfamilies: Caesalpinoideae, Cercidoideae LPWG (2017), Detarioideae Burmeister (1837), Dialioideae LPWG (2017), Duparquetioideae LPWG (2017), and Papilionoideae, as well as a mimosoid clade, based primarily on molecular work and supported by morphological data. Styphnolobium is one of 503 genera in Papilionoideae and includes nine species ( POWO 2023). As best we can determine, there are wood anatomical descriptions for only two species: S. japonicum (L.) Schott (1830) (native to central and southern. China) and S. affine (native to Arkansas, Louisiana, Oklahoma, and Texas in the USA) ( Fujii et al. 1994, Gasson 1994, Itoh et al. 2022); both are ring-porous. The other species of Styphnolobium are native to Central America, with one species extending into Columbia; some species grow in seasonally dry tropical biomes, some in wet tropics. The Chinese species belongs to Section Oresbios (Rudd) M. Sousa (1993) ; the American species to Section Styphnolobium . Because of the relatively few samples available to us we are not sure whether there are wood anatomical differences between the two Sections.

Comparisons to fossil woods— The middle Eocene Clarno Nut Beds has three types of legume woods; all differ from the Dietz Hill wood as they are diffuse-porous ( Wheeler and Manchester 2002). Müller-Stoll and Mädel (1967) reviewed the fossil wood record of the Leguminosae and at that time recognized only 19 fossil genera. Because it is difficult to distinguish some present-day legume genera from one another, most of their genera accommodate more than one present-day genus. Their key to the genera included only two ring-porous genera: Robinioxylon Müller-Stoll and Mädel (1967) (differs in having latewood vessel clusters, storied axial parenchyma) and Gleditsioxylon Müller-Stoll and Mädel (1967) (rays often>10-seriate). Given that present-day Leguminosae comprises over 750 genera ( LPWG 2017),it is not surprising that there are fossil legume woods that do not fit the 19 genera recognized in 1967.

More recently, the genus Cercioxylon Akkemik (2019) was created for a Pliocene wood considered to resemble Cercis L. (1753) and described as having ring- to semi-ring-porous wood. It differs from this Dietz Hill wood because it does not have a well-defined narrow earlywood zone (Akkemik 2019, Plate V) and it is described as having vessel clusters common and storied axial parenchyma.

Figures

Figure 7. Caption on pg, 15 Figure 7. Fabaceae. cf. Styphonolobium sp., UF 278-84867. A. Ring-porous wood, with distinct earlywood zone 2‒3 vessels deep, confluent-banded axial parenchyma, TS. B. Pith and first formed secondary xylem, first formed growth ring not ring-porous, pith with thin-walled parenchyma cells, TS. C. Earlywood vessels mostly solitary, one radial pair; latewood vessels in small multiples, confluent parenchyma, TS. D. Crowded alternate pits, TLS. E. Vessel-ray parenchyma pits similar to intervessel pits, RLS. F. Multiseriate rays; axial parenchyma strands of 2‒4 cells, TLS. G. Multiseriate rays; non-septate fibers, TLS. H. Simple perforation plate in narrow vessel element; heterocellular rays with procumbent and square cells, RLS. I. Pith (at right) with thin-walled parenchyma cells, upright cells common in rays nearest to pith (at left), RLS. Scale bars=500 µm in A; 200 µm in B, I; 100 µm in C, F; 50 µm in G, H; 20 µm in D, E.