Aesculus constabularisii, Wheeler & Manchester & Baas, 2023

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 : 32-33

AESCULUS CONSTABULARISII SP. NOV.

FIG. 16A–L

Diagnosis— Wood diffuse-porous to semi-ring-porous. Vessels solitary and in short radial multiples. Mean tangential diameters <100 µm. Perforation plates simple, intervessel pits alternate, small to medium; vessel-ray parenchyma pits similar to intervessel pits. Widely spaced helical thickenings throughout the vessel elements.

Fibers non-septate.

Axial parenchyma not common, some scanty paratracheal and marginal.

Rays exclusively uniseriate; homocellular, composed of procumbent cells, non-storied.

Holotype — UF 278-84887 , estimated maximum diameter 10+ cm.

Etymology— Named for Adam Constabularis, NC State Library IT guru, who watches over the InsideWood web site.

Occurrence— Dietz Hill ( UF 278).

Description— Growth rings present, marked by radially narrow fibers.

Wood diffuse-porous to semi-ring-porous with a concentration of vessels at the beginning of a growth ring ( Fig. 16A–C ); vessels solitary and in radial multiples of 2–3 (rarely 4–5); mean tangential diameter 83 (17) µm, range 44–105 µm; 61–74 vessels/mm 2. Perforation plates simple ( Fig. 16E–F, J, K ); intervessel pits alternate ( Fig. 16G ), horizontal diameter 5.5–7.5 µm. Vessel-ray parenchyma pits slightly smaller than intervessel pits ( Fig. 16H ). Vessel element lengths 302–438–588 µm; vessel element end walls inclined. Widely spaced inclusions present ( Fig. 16J ). Helical thickenings throughout vessel elements ( Fig. 16K, L ).

Fibers thin-thick-walled, non-septate, pitting not observed ( Fig. 16K ).

Axial parenchyma not common, some scanty paratracheal, and some in growth ring margins.

Rays exclusively uniseriate ( Fig. 16I–K ). Average ray height 11 cells, range 4–26. Homocellular, composed of procumbent cells ( Fig. 16L ), 8–12 per mm, non-storied.

Oil/mucilage cells and crystals not observed.

Comparisons with modern woods— In the InsideWood database, only genera of Sapindaceae have this combination of features: wood not ring-porous (3a), vessels solitary and in short multiples with a random arrangement (6a 7a 8a 9a 10a), simple perforation plates (13p), alternate intervessel pit small-medium (22p 24a 27a), vessel-ray parenchyma pitting similar to intervessel pitting (30p), helical thickenings throughout vessel elements (36p 37p), vessel diameter not large (43a), non-septate fibers without obvious pits (61p 66p), axial parenchyma not conspicuous (77a 79a 80a 83a 84a 85a 86a), exclusively uniseriate homocellular rays (96p 104p). Of the eleven matching genera, only Aesculus has exclusively non-septate fibers, the other genera have predominantly septate fibers.

Consequently, we consider this wood to belong to the Sapindaceae , Tribe Hippocastaneae , a tribe with a disjunct distribution ( Stevens, 2001 -onwards). Kew’s Plants of the World ( POWO 2023) recognizes 12 accepted spe- cies of Aesculus . Wood anatomical differences between the species include vessel-ray parenchyma pitting type, diameter and abundance of vessels, presence/absence of storied rays or marginal parenchyma. Klaassen (1999) noted that Handeliodendron Rehder (1935) wood is nearly identical to Aesculus , but it has only heterocellular rays. Both genera have widely spaced helical thickenings in the vessels, a unique feature within the Sapindaceae ; in other sapindaceous genera with helical thickenings the thickenings are closely spaced ( Klaassen 1999, Itoh et al. 2022).

The clades recovered by phylogenetic analyses of the Sapindaceae (e.g., Xiang et al. 1998, Harris et al., 2009, Du et al., 2020) generally align with the five groups recog- nized on the basis of morphology by Hardin (1957). The exception is the position of Aesculus californica (Spach) Nutt. (1838) , which was recovered as belonging Section Calothyrsus Spach (1834) along with the Asian species, A. chinensis Bung e (1833), A. assamica Griff. (1854) , A. indica (Wall. ex Cambess.) Hook. (1859) . All the aforementioned species have vessel-ray parenchyma pits similar to the intervessel pits ( IAWA feature 30). There are no wood anatomical descriptions for species in Sections Macrothyrsus Spach (1834) or Parryana. Available information on Section Pavia indicates its species differ as they have horizontally elongate vessel-ray parenchyma pits with reduced borders. Section Aesculus species ( A. turbinata Blume, 1847 , A. hippocastanum L., 1753) have storied structure or a tendency to it as do A. chinensis and A. indica of Section Calothyrsus Spach (1834) .

The concentration of vessels at the beginning of a growth ring is unusual for Aesculus , but a tendency to this feature occurs in some samples of A. turbinata and A. chinensis . In most extant Aesculus the vessels are more crowded than in this fossil, but in some A. indica and A. californica samples the vessels are as widely spaced as in this late Eocene wood. Available information on present-day Aesculus wood anatomy suggests that A. klaassenii belongs to Section Calothyrsus because it has vessel-ray parenchyma pitting similar to intervessel pitting and is closest to A. californica because it lacks storied structure.

Comparisons with fossil woods— We only know of five reports of fossil woods suggested to be related to Aesculus (Gregory et al. 2009) . There are three Miocene woods that we consider reliably assigned to Aesculus : A. hankinsii Prakash and Barghoorn (1961) from Washington, USA; A. mioxyla Suzuki and Terada (1996) from Japan; Aesculus sp. from Korea ( Jeong et al. 2004). All three are strictly diffuse-porous with vessels more crowded than this Eocene wood. Aesculus hankinsii differs as its numerous vessels are evenly distributed throughout the growth ring and rays show a tendency to storied structure. Aesculus mioxyla also has evenly distributed vessels as well as weakly storied rays. Two reports are questionable as their descriptions lack the details (e.g., vessel-ray parenchyma pits) necessary to confirm relationships with Aesculus or the Sapindaceae : Aesculoxylon deccanense Trivedi and Srivastava (1982) from the Deccan Intertrappean Beds and Aesculus sp. from the Eocene of Montana ( Yamamoto and Chadwick 1982). Since this Dietz Hill wood is assignable to Aesculus , but does not match any extant or fossil species, we have assigned it to the new species, A. klaassenii .

Figures

Figure 16. Caption on pg. 35.