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

Tribe Spondioideae TAKHT.

Genus cf. Pentoperculum (E.REID et M.CHANDLER) MANCHESTER

Text-fig. 5a–f

M a t e r i a l. Three specimens USNM PAL. 772349,

772359, 772360.

D e s c r i p t i o n. Endocarp broadly ovate in lateral view, the lower half shallowly dish-shaped ( Text-fig. 5a ), the upper portion an inverted bowl containing six locules. Round to polygonal in cross section, the polygon reflecting the number of locules ( Text-fig. 5b, c ). USNM 772359 height 11.8 mm, width 13.9mm × 14.2 mm; USNM 772360 height 12mm, width 14 mm × 14.5mm, USNM PAL 772349 height 8.8 mm, width 11.0 × 11.8mm. The base slightly rounded to flat, bearing a circular pit of attachment ca. 1 mm in diameter ( Text-fig. 5c ). In each specimen the ridges radiate from the basal scar to the equator of the endocarp, terminating opposite the base of the locules, the ridges thus as many in number as locules. In USNM 772359 there are twice as many ridges, the ridges both opposite and alternating with the locules. The apex rounded, often eroded, with six axially-elongate valves that average 6.4mm long (range 5.8–6.9 mm) and 3.7mm wide (range 3.4–3.9 mm). These valves are bipartite, the center marked by a longitudinal groove ( Text-fig. 5a, d ). No internal anatomy is discernible, and there are no apparent depressions on the surface.

D i s c u s s i o n. The structure of these multi-carpellate, operculate endocarps clearly allies them with the subfamily Spondioideae of the Anacardiaceae ( Wannan and Quinn 1990, Mitchell et al. 2006, Herrera et al. 2018). Among living genera, the possession of 6 carpels is more like extant Pleiogynium ENGL. which exhibits 5–12 carpels, than the remaining genera of Spondioideae , which possess from one to, at most, 5, mature carpels. However, Pleiogynium lacks bipartite opercula. Two living genera ( Haematostaphis HOOK.F. , Pseudospondias ENGL. ) and the extinct Pentoperculum MANCHESTER exhibit bipartite opercula ( Hill 1933, 1937, Herrera et al. 2018), whereas unitary opercula are noted in other genera, e.g., Antrocaryon PIERRE , Dracontomelon BLUME and Sclerocarya HOCHST. The fruit morphology of all extant genera of Spondioideae was reviewed by Herrera et al (2018).

Reid and Chandler (1933) noted the presence of basal or sub-equatorial pores that link with lacunae in the endocarp wall of several living species of Dracontomelon , features observed by other authors (e.g., Hill 1933, Chesters 1957, Tardieu-Blot 1962, Wilkinson 1968). These characters, seen also in the Clarno specimens of Pentoperculum , are not present in the Wagon Bed fossils – possibly because of the limited detail preserved in these casts.

On the basis of the available characters, these Wagon Bed fossils cannot be clearly allied with any extant genus. These fossils are similar in many respects to Pentoperculum minimum (E.REID et M.CHANDLER) MANCHESTER ( Manchester 1994) from the early Eocene London Clay and middle Eocene Clarno Formation in general appearance, and the possession of bipartite opercula.Although that genus usually has five locules, occasional 4- and 6-locular specimens were also observed ( Manchester 1994). However, the Wagon Bed specimens lack internal detail and are about twice the size of those from Clarno. A second Pentoperculum species from London Clay, “ Dracontomelon ” subglobosum E.REID et M.CHANDLER (Manchester and Collinson, in progress), has larger endocarps similar in size to the Wagon Bed fossils, but possesses 5 locules.

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.