Langtonia bisulcata E.REID et M.CHANDLER, 1933

Manchester, Steven R. & Collinson, Margaret E., 2022, Mastixioid Fruits (Cornales) From The Early Eocene London Clay Flora: Morphology, Anatomy And Nomenclatural Revision, Fossil Imprint 78 (1), pp. 310-328 : 321-325

Langtonia bisulcata E.REID et M.CHANDLER, 1933

Text-fig. 10a–j

H o l o t y p e. V.22984 (Natural History Museum,

London).

R e m a r k s. Langtonia was established and identified as an extinct mastixioid genus by Reid and Chandler (1933). Langtonia bisulcata fruits are elongate-ellipsoidal with smooth to shallowly ridged surface. The fruits have endocarps composed of tortuous fibres ( Text-fig. 10g –j ) surrounded by a thin mesocarp and epicarp covering (Textfig. 10j). Endocarps vary greatly in size from 9 to 20 mm long in the London Clay ( Reid and Chandler 1933) and from 16 to 35 mm long in the Clarno Nut Beds ( Manchester 1994). The fruits are bilocular, sometimes with both locules well developed ( Text-fig. 10d ), but commonly with one of the locules abortive ( Text-fig. 10c, g, h ). Unlike the other extant and fossil genera of Mastixiaceae , each germination valve of Langtonia has two dorsal infolds resulting in a locule that has the shape of a ε in cross section ( Text-fig. 10c–h ). Contrary to the situation in Mastixia and Eomastixia , where ovular bundles follow the germination valve boundaries, the vascular bundles of Langtonia are scattered, situated mainly in the septal area in the endocarp on the ventral side of each locule. The germination valves lack prominent vascular bundles. The locule is lined by a uniseriate layer of relatively large rectangular cells ( Text-fig. 10i ).

Kirchheimer (1957) questioned the affinity of Langtonia to Mastixiaceae because of the double infolds which are not seen in any other mastixioids. However, the woody endocarps with elongate germination valves, and pendulous anatropous seeds with ventral raphe ( Reid and Chandler 1933: pl. 25, fig. 21, Manchester 1994: pl. 11, fig. 5) support Reid and Chandler’s assignment. The endocarps have elongate germination valves that extend the full length of the locule as in extant Mastixiaceae , contrasting with the apically confined valves of Nyssaceae ( Amersinia MANCHESTER, P.R.CRANE et GOLOVN., Camptotheca DECNE. , and Nyssa L.; fig. 12 in Manchester and Hickey 2007).

In western North America the same genus and species is known from permineralized fruits in the Eocene Clarno Formation ( Manchester 1994) and by the distinctive endocarp molds and locule casts from Paleocene Fort Union Formation ( Tiffney and Haggard 1996). Although well represented in the London Clay, Langtonia has not been observed in the carpofloras of continental Europe. Most specimens are preserved with only the endocarp remaining, but one of the Clarno specimens with intact soft tissue (Textfig. 10h–j) shows the presence of longitudinal canals (Textfig. 10j) similar to those seen in extant Mastixia ( Manchester and Collinson 2019: pl. 1, fig. 11).

Figures

Text-fig. 10. Langtonia bisulcata REID etCHANDLER. a, b, e–g: Holotype, V. 22984, from micro-CT data. a: Dorsiventral view surface rendering. b: Dorsiventral view translucent volume rendering showing outline of locule cast. c: Equatorial transverse fracture showing paired dorsal infolds and locules with shape of a ε in cross section, reflected light, V. 22993. d: Digital transverse section from micro-CT data, of fruit with two well developed ε-shaped locules, V. 22985. e–g: Successive digital transverse sections with one well developed ε-shaped locule and infolds of the abortive locule visible in (g) (arrows). h–j: Physical transverse thin sections of specimen from middle Eocene Clarno Formation, Oregon, USA with well-preserved mesocarp including longitudinal canals in (j) (arrows), USNM 424875; Scale bars 0.5cm in (a, b), 2.5mm in (c–g), 5mm in (h), 2mm in (i), 1mm in (j); (a, b) share same scale bar; (c, d) share same scale bar; (e, f, g) share same scale bar.