Spondioideae TAKHT.

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 : 61-63

Tribe Spondioideae TAKHT.

Genus cf. Pleiogynium ENGL.

Text-fig. 5j–m

M a t e r i a l. One fruit replaced by chalcedony, USNM

PAL 772357.

D e s c r i p t i o n. Endocarp subglobose, but wider below the equator than above ( Text-fig. 5j, k ), roundedelliptical in transverse view, height 16 mm, diameter 15.5 × 18.4 mm. The base slightly rounded to flat, bearing a circular pit of attachment ca. 1 mm in diameter ( Text-fig. 5m ). The apical surface smoothly rounded. Nine locules, each with an elliptical germination aperture; germination apertures in a cycle extending from the equator toward the fruit apex ( Text-fig. 5j, k ). One locule ( Text-fig. 5j , left side) covered by a bulging surface 5.2 mm high by 3.9 mm wide, with no sign of being bipartite. Locules possessing a bipartite inner lining ( Text-fig. 5k ). Ridges radiate from the basal scar to the equator of the endocarp, aligned with the locules.

D i s c u s s i o n. This is the largest of the Spondioid fruits from the Wagon Bed flora and possesses 9 locules ( Text-fig. 5l ). In the high number of locules, the fruit resembles extant Pleiogynium , which is distinguished from other genera of the Spondioideae that are typically 1- to 5-locular. Eight of the exposed locules on this specimen have open apertures, but one is covered with a bulging surface.Although rounded opercula are characteristic of some extant Spondioid genera, such Poupartia COMM. ex JUSS. , Antrocaryon , etc., Pleiogynium locules lack opercula ( Rozefelds et al. 2015, Herrera et scans. s: Equatorial transverse section. t: Longitudinal section perpendicular to primary septum, note thick primary septum (arrow). u: Longitudinal section parallel to primary septum transecting one of the cotyledons; note narrow secondary septum at base (arrow). v: Longitudinal section in plane of the primary septum; note apical aperture (A) connecting the two main lobes of the locule and divergent pair of placental bundles arising from base (arrows). w: Transverse section in apical 1/3 of nut showing the connection between the two main lobes of the locule via the aperture seen in (v). x: Transverse section of the base of the nut showing the four lobes of the locule separated by the primary and secondary septa. Note placental bundles in primary septum (arrows).

al. 2018). Rather, the locule is lined by a bipartite locular envelope that opens “like a pair of lips or clam-like valves” ( Herrera et al. 2018). These valves are not obvious and in un-germinated fruits may be covered by the exocarp, perhaps explaining the “bulge” illustrated over one of the locules in Text-fig. 5j . The other locules of the same specimen are open to the surface. Due to the lack of anatomical preservation, our assignment of this fossil remains tentative. However, the number of locules, and the bipartite inner locule lining are strongly suggestive of Pleiogynium .

Figures

Text-fig. 5. Anacardiaceae (a–m), Burseraceae (n–q). Scale bars = 1cm. a–f: Pentoperculum sp. a–c: USNM PAL 772360. a: Lateral view of endocarp, apex up; three germination valves visible, the central clearly displaying the bipartite nature of the valve, reflected light, palladium coated. b: Apical view displaying six locules, with two preserved germination valves at the lower left, reflected light, palladium coated. c: Basal view of the endocarp, the locules suggested by swellings; note point of attachment, micro-CT scan surface rendering. d–f: Pentoperculum sp. USNM PAL 772359, reflected light, palladium coated. d: Lateral view of a probable 6-loculed endocarp, apex up; a single intact germination valve in the center, displaying the central lineation that divides it in two. e: Apical view; two bi-partite germination valves are visible, indicated by arrows to the middle cleavage line of two of the valves. f: Basal view, the locules suggested by the undulations in the margin. g–i: Indet. Spondioideae. USNM PAL 772358, reflected light, palladium coated. g: Lateral view of multi-locular endocarp, apex up. h: Apical view showing finely punctuate surface and peripheral locule cavities. i: Basal view. j–m: Cf. Pleiogynium USNM PAL 772357. j: Lateral view of the multi-locular endocarp, apex up; note intact germination valve on left and exposed locule facing the viewer, micro-CT scan surface rendering. k: Lateral view, rotated about 30° from (j), showing three exposed locules, reflected light, palladium coated; note bipartite locule lining at center. l: Apical view of the multilocular endocarp; the locule with intact germination valve at the upper right, reflected light, palladium coated. Arrows to each locule. m: Basal view showing central point of attachment and prominent radiating ridges aligned with the locules, micro-CT scan surface rendering. n–q: Canarium, USNM PAL 772361. Scale bar = 1cm. n: Lateral view of endocarp directly facing one germination valve flanked by two strong ridges; apex up; specimen coated in sodium nitrate and photographed by R. A. Scott. o: Lateral view facing one of the three pronounced ridges, flanked to the left and right by two germination valves; apex up. p: Apical view displaying the three strong ridges, arching over the apex and flanking three deep embayments, covered with germination valves. q: Basal view, the three ridges being less pronounced. o–q: Reflected light, palladium coated.