Carya NUTT.

Tiffney, Bruce H. & Manchester, Steven R., 2022, The Early Middle Eocene Wagon Bed Carpoflora Of Central Wyoming, U. S. A., Fossil Imprint 78 (1), pp. 51-79 : 59-61

Genus Carya NUTT.

Text-figs 3a–x , 4a–w

M a t e r i a l. Ten specimens, four whole, three half nuts and three more fragmentary. Many chalcedony casts. Three specimens exhibiting casts of the seed, one specimen permineralized and displaying some internal structure. USNM PAL 772346 , 772347 , 772348 , 772350 , 772351 , 772352 , 772353 , 772354 , 772355 , 772356 .

D e s c r i p t i o n. Nuts ovoid in side view, almost circular in cross section, but with a sense of a four angled symmetry (e.g., Text-fig. 3c ), unilocular, with a single seed. Of the eight reasonably complete full or half nuts the average height is 27.2 mm (range 23.7 to 30.5 mm), the diameter parallel to plane of dehiscence average 22.6 mm (range 19.5 to 27 mm), and the diameter perpendicular to plane of dehiscence average 22.5 mm (range 19.1 to 28.4 mm). Surface smooth, often marked by eight very fine longitudinal grooves (Textfig. 4b, c, u). Base generally rounded, although in some cases with a slight protrusion. Lateral walls 3–4mm thick, possibly thickening towards the base. Primary septum (perpendicular to plane of dehiscence) 2 to as much as 5 mm wide at base, tapering to 1 to 2 mm at apex, and extending ~3/4 of the distance to the top of the locule ( Text-figs 3e, m, n, s, t, x , 4g, h, p, q, v, w ). A pair of placental vascular bundles arises at the base of the primary septum, but these bundles soon diverge (e.g., Text-fig. 3l, n, v ), each arching close to the periphery of the primary septum, rather than running parallel to the nut axis. Secondary septum present near base of the nut, and, along with the primary septum, dividing the base of the locule into four lobes ( Text-figs 3n, x , 4k ); secondary septum shorter and narrower than the primary septum. Interior of locule smooth with no inner ribs. Locule narrower in the plane of the primary septum (10 mm) than perpendicular to it (14 mm). Two narrow, continuous, lacunae present in the wall of the nut, originating approximately 1/4 of the way from the base of the fruit and extending to near the apex; possibly bifurcated at the base, but coalescing into a single arcuate cavity in each half of the nutshell, enveloping the locule towards the apex ( Text-figs 3j, k, m , 4i, j ). Cellular structure present in one specimen, where a cross-section reveals the core of the nut to be composed of equiaxial cells. In others, the exterior displays radiating structure that might represent radially-elongate mineral fibers ( Text-figs 3i, j , 4q ). Seed elongate, 12 mm wide × 17 mm high with a convex shoulder region ( Text-fig. 4f, h, l ); seed coat thin ( Text-fig. 4j ) and apparently papery.

D i s c u s s i o n. The fossils are clearly nuts of the Juglandaceae , with a resemblance to both Juglans L. and Carya . Some specimens appear to be isolated nuts without preservation of the surrounding husk, but in others the nutshell is permineralized and appears dark in reflected light, and is surrounded by a distinct, but less well preserved lighter colored layer that may represent the husk (as seen in Text-fig. 3i–m, u, v ). Scott (1954), Leroy (1955), Manchester (1987) and Manchester and McIntosh (2007) provide characters to distinguish these two genera. While the mode of preservation impedes determination of some of these characters (e.g., dehiscence of the husk, complete path of placental bundles within the nut), others can be evaluated. Our discussion below progresses from characters that suggest affinity with Carya to those that are less decisive.

The smooth surface seen in the fossils is more commonly characteristic of Carya than Juglans , although it can occur in some modern species of the latter. There is a hint of a protuberant base in three of the Wagon Bed fossils similar to the condition in Carya ( Manchester 1987) . The position of the pair of placentary bundles, whether running parallel and adjacent to the central axis as in Juglans , or diverging from one another near the base and following a peripheral course before converging toward the seed apex as in Carya , is an important distinguishing feature ( Leroy 1955), but the configuration is not well preserved in most of these specimens. However, by moving through virtual slices of the two permineralized specimens shown in Text-fig. 3j–n and s–x , we were able to follow the faint traces of these bundles. Although the bundles are closely adjacent at the base of the nut ( Text-fig. 3n ), longitudinal sections in plane of the primary septum ( Text-fig. 3l ) show that they quickly diverge and assume a peripheral course in the manner of Carya . The seed has a rounded shoulder, is axially elongate within the locule, and is distinctly narrower in plane of primary septum and wider perpendicular to it ( Text-fig. 4l ), all characteristic of Carya ( Manchester 1987, Manchester and McIntosh 2007). The available characters of the Wagon Bed specimens conform more closely to Carya than to Juglans and are reminiscent of the specimens from Post, Oregon ( Manchester and McIntosh 2007) and the European Cenozoic ( Mai 1981). These represent one of the oldest occurrences of Carya nuts, the next oldest being those from the late Eocene of Oregon ( Manchester and McIntosh 2007) and Neogene of Europe ( Mai 1981). Carya is also represented by pollen in the Wagon Bed flora ( Leopold and MacGinitie 1972). In the current day, Carya comprises some 18–24 species of temperate trees, distributed in North and Central America, with a lesser diversity in eastern Asia ( Mabberley 2008).

Turning to those characters that are less indicative of Carya , the presence of inner ribs perpendicular to the median septum is characteristic of Carya ( Manchester 1987) . These are missing in the fossil, although fig. 3, 1 in Manchester (1987) suggests these may be very subdued in some cases. This is also true of some living species, e.g., in extant Carya poilanei (A.CHEV.) J.-F.LEROY of Vietnam and Southern China ( Mai 1981, Zhang et al. 2022). The nuts of Carya possess a four-angled amb ( Manchester 1987), a character only mildly expressed in two of the ten fossils presented here ( Text-figs 3c , 4b ), although many are casts with some

Coryloides locule cast, USNM PAL 772345, scale bar = 1 cm. o: Lateral view illustrating a disk-like structure at top surmounted by a central point, and the rumpled appearance of the surface, suggesting a possibly flexible texture. p: Lateral view rotated 90°, disk up, the separation between the pointed disk and the rest of the fossil distinct (arrows). q: Lateral view rotated 180° from (p). r: Apical view with circular disk and central point. p–q: Micro-CT scan surface rendering. r: Reflected light, palladium coated.

distortion of the exterior surface. Nuts of Juglans generally possess prominent multilobed lacunae in their walls; lacunae are lacking in many species of Carya except in sections Apocarya and Sinocarya ( Manchester 1987) which possess simple lacunae. Narrow lacunae are readily observed in the permineralized Wagon Bed specimens (e.g., Text figs 3e, j–m, 4i, j), and are present in specimens of Carya from the late Eocene of Oregon ( Manchester and McIntosh 2007).

Figures

Text-fig. 3. Juglandaceae. Carya (a–x). Scale bars = 1cm. a–e: USNM PAL 772346. Micro-CT scan surface rendering. a, b: Lateral, c: apical, d: basal views. e: Virtual equatorial transverse section. f–n: USNM PAL 772347. f: Lateral view, reflected light, showing path of saw cut for transverse section of (i). g: Basal view, reflected light. h: Apical view, micro-CT surface rendering. i: Physical transverse section displaying locule and cellular preservation of parts of wall. j–n: Virtual sections from micro-CT scan data. j: Transverse section at apical 1/3 of nut. Note narrow lacunae (arrows). k: Longitudinal section parallel to primary septum, traversing one of the cotyledon lobes and showing secondary septum at base. l: Longitudinal section in plane at right angles to (k) in plane of primary septum, showing divergent placental bundles arising from base of nut (arrows). m: Equatorial transverse section showing two lobes of locule separated by primary septum. n: Transverse section near base of nut showing primary and secondary septa, creating four basal lobes of locule; note diverging placental bundles (arrows). o–x: USNM PAL 772351. o: Lateral view of broken nut with exposed locule cast, reflected light. p: Same orientation of nut, micro-CT surface rendering. q: Same specimen lateral view, rotated 90° from (p), micro-CT surface rendering. r: Apical view, reflected light. s–x: Virtual sections from micro-CT

Text-fig. 4. Juglandaceae Carya (a–w). Scale bars = 1cm. a–d: USNM PAL 772352, reflected light, palladium coated. a: Obliquelateral view of nut, apex up. b: Basal view with damage to left and clear depiction of meridional grooves. c, d: Two lateral views oriented about 130° from each other and avoiding the area of damage; the meridional grooves clear in (c). e–l: USNM PAL 772350. e: Intact nut, lateral view, apex up, reflected light. f: One half of split nut revealing in situ chalcedony locule cast, reflected light. g–k: Virtual sections from micro-CT data. g: Longitudinal section parallel to the exposed face in (f). h: Longitudinal section at 90° from (g). i: Transverse section in apical 1/3 showing locule bracketed by C-shaped lacunae (arrows). j: Equatorial transverse section showing two lobes of the locule separated by primary septum, lacuna evident below as white line. k: Transverse section near base