Saxifragispermum E.REID et M. CHANDLER

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 : 56

Genus Saxifragispermum E.REID et M. CHANDLER

Text-fig. 2a–g

M a t e r i a l. One specimen, silicified exterior with original internal organic material. USNM PAL 772341.

D e s c r i p t i o n. A loculicidal capsule, narrowly ovate to ovate in side view ( Text-fig. 2a, b ), rounded/four angled in cross section ( Text-fig. 2c–d ), 10.2 mm long and 4.1 × 4.9 mm in width. The four angles each with a central linear groove suggestive of a plane of weakness ( Text-fig. 2a, b ). The grooves meet at the pointed apex and converge on an inflated and protruding point of attachment at the base. The grooves circumscribe four valves that are evenly pitted on their surface. An equatorial transverse cut revealed a geode lined by quartz crystals, lacking preservation of wall structure and placentae, but with central cavity filled with ovoid structures resembling seeds within a tangle of soft, whitish threads interpreted as trichomes or fibers ( Text-fig. 2e–g ).

D i s c u s s i o n. This specimen resembles, in its exterior form, the fruits of Saxifragispermum spinosissimum E.REID et M.CHANDLER , previously described from the London Clay flora ( Reid and Chandler 1933, Chandler 1961), and S. tetragonalis MANCHESTER from the Clarno flora ( Manchester 1994). While the specimens from those sites are permineralized and preserve the cellular structure of the fruit, the Wagon Bed specimen is a cast with a hollow center. Cutting the specimen transversely in half revealed a peripheral lining of quartz crystals and a central unmineralized cavity filled with apparent original material including a matrix of thin whitish threads that might be trichomes or fibers, surrounding brown ellipsoidal structures resembling seeds ( Text-fig. 2e, f ). Despite the implications of the generic name Saxifragispermum as assigned by Reid and Chandler (1933), it was subsequently allied with the Flacourtiaceae DC. ( Chandler 1961, Manchester 1994) which has been subsumed in the Salicaceae ( Boucher et al. 2003) . Assignment of the Wagon Bed specimen to this family cannot be absolutely confirmed because the distinctive parietal placentation seen in the London Clay and Clarno specimens is not preserved. However, the overall morphology of the fruit (four-valved, angled capsule, coupled with seeds embedded in a fibrous matrix) closely resembles that of the London Clay and Clarno taxa, although the Wagon Bed specimen is closer in size to the Clarno species.

The thread-like locule filling of this specimen, like that of the Clarno and London Clay specimens, is suggestive of the tightly packed plumed seeds of extant Salix L. and Populus L. fruits. The Wagon Bed occurrence extends the North American range of the genus to the Rocky Mountains. In the Green River Formation, Salicaceae are represented by compressed fruit capsules as well as leaves of Populus ( Manchester et al. 2006) and Pseudosalix L.BOUCHER , MANCHESTER et JUDD ( Boucher et al. 2003). Although it is difficult to make a detailed comparison because of the different modes of preservation, there is a noteworthy similarity between Saxifragispermum and the capsules of Populus tidwellii MANCHESTER et JUDD from Utah and P. cinnamomoides (LESQ.) MACGINITIE from Wyoming as illustrated in Manchester et al. (2006: e.g., figs 5e, f, 6g –k).

Figures

Text-fig. 2. Salicaceae (a–g), Cannabaceae (h–n), cf. Betulaceae (o–r). a–g: Saxifragispermum, USNM PAL 772341. Scale bar = 5mm except as indicated. a–b: Lateral, c: apical, and d: basal views of fruit, reflected light, palladium coated; apex at top of (a, b). e: Equatorial transverse section reflected light; arrows indicate presumed seeds, scale bar = 2mm. f: Detail of locule contents extracted from (e), transmitted light, scale bar = 200 Μm. g: Interwoven trichomes or fibers from locule, transmitted light, scale bar = 5 Μm. h–j: Celtis. h, i: USNM PAL 772342, reflected light, palladium coated, scale bar = 5mm. h: Lateral view parallel with plane of dehiscence. i: Lateral view perpendicular to plane of dehiscence. j: DMNH EPI.47809, Celtis in lateral view; showing reticulate sculpture and the vertically-oriented, plane of dehiscence (arrow), scale bar = 5mm. k–m: Aphananthe. USNM PAL 772344, reflected light, palladium coated, scale bar = 5mm. k: Apical view, note triangular cross section and apical plug (arrow). l: Lateral view, apex up. m: Lateral view at 90° to (l). n: Detail of cellular pattern at surface of endocarp, scale bar = 0.5 mm. o–r: