Diplopanax cacaoides (ZENKER) Manchester & Collinson, 2022

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 : 312

Diplopanax cacaoides (ZENKER) MANCHESTER et M.E.COLLINSON comb. nov.

Text-fig. 1a–f, h–j

1832 Baccites cacaoides ZENKER , p. 10, pl. 1, figs (E) and 4–8, 11–16.

1933 Mastixia cantiensis E.REID et M.CHANDLER , p. 448, pl. 25, figs 1–3 only.

1978 Mastixicarpum cacaoides (ZENKER) MAI in Mai and Walther, p. 120, pl. 44, figs 13–22.

1993 Mastixicarpum cacaoides (ZENKER) MAI ; Mai, p. 59.

B a s i o n y m. Baccites cacaoides Z ENKER (Zenker 1832: Beiträge zur Naturgeschichte der Urwelt, p. 10, pl. 1, figs (E) and 4–8, 11–16; Altenburg, Weisselster Basin, Germany).

P l a n t F o s s i l R e g i s t r y N u m b e r. PFN002904

(for new combination).

N o m e n c l a t u r e. Rather than making a new combination which would preserve the epithet cantiensis , we are required to use an epithet that was established earlier by Zenker (1832) because the specimens from Weisselster Basin, Germany ( Mai and Walther 1978) and the London Clay are conspecific.

D e s c r i p t i o n a n d r e m a r k s. The holotype of Mastixia cantiensis ( Text-fig. 1a–d, h–j ) conforms to the extant genus Diplopanax in having clearly defined planes of weakness demarcating the germination valve ( Text-fig. 1h, i ), and by the dispersed rather than paired ovular bundles as illustrated and described earlier for the extant species (pp. 54– 57 and pl. 2 in Manchester and Collinson 2019). The fruits of this fossil species are unilocular, ovoid to cylindrical, rounded basally and rounded or truncate apically, 17 to 32 mm long and 12 to 22 mm wide. The locule is horseshoe-shaped in cross section. The germination valve is elongate. The endocarp wall is up to 9 mm thick, composed of radial fibres, with scattered vascular bundles and secretory canals ( Text-fig. 1h–j ), but usually without larger cavities.

Synonyms of Diplopanax cacaoides cited by Mai 1993 include Platymastixia cocaoides (ZENKER) KIRCHH. ( Kirchheimer 1934: 790, fig. 21) and Mastixicarpum compactum KIRCHH. ( Kirchheimer 1935) from the Weisselster Basin, Germany ( Mai and Walther 1978). For comparison with the London Clay specimens ( Text-fig. 1a–f, h–j ), we illustrate a specimen from the Miocene of Wiesa, Germany ( Text-fig. 1g ). With the exception of the type material of Mastixicarpum M.CHANDLER from Hordle, most other species formerly attributed to that genus are now considered to represent Diplopanax ( Eyde and Xiang 1990, Czaja 2003, Manchester and Collinson 2019). Czaja (2003) recognized a common Miocene species, D. limnophilus (UNGER) CZAJA (see also Ševčík et al. 2007). Similar Diplopanax fruits were also present in the Eocene of western North America (e.g., late Eocene Diplopanax sp. from late Eocene Quimper Sandstone, Oak Bay, Jefferson Co., Washington; fig. 33 in Manchester et al. 2009). Diplopanax eydei STOCKEY, LEPAGE et PIGG described from the middle Eocene of Princeton, British Columbia, Canada ( Stockey et al. 1998), conforms in general morphology, but has smaller fruits and preserves a thick epicarp of isodiametric cells not observed in other modern and fossil species of the genus. In our current understanding, the London Clay occurrence is significant as the oldest representative of the genus Diplopanax .

Figures

Text-fig. 1. Diplopanax cacaoides (ZENKER) comb. nov. a–d: [Holotype of Mastixia cantia E.REID et M.CHANDLER, V.22953]. a: Lateral view of longitudinally broken specimen, reflected light. b–d: Surface renderings from micro-CT data. b: Lateral view of longitudinal fracture surface. c: Same specimen rotated to show external surface. d: Enlargement of lower half from (a, b), reflected light. e, f: Specimen figured originally as a paratype of M. cantia, V.22954 (Reid and Chandler 1933: pl. 25, fig. 3), reflected light. e: Ventral view with much of the endocarp wall fallen away exposing smooth convex ventral surface of locule cast. f: Transversely fractured surface, showing thick wall of the endocarp, and dehiscence plane leading to the left limb of the locule. g: Transversely sectioned, laterally compressed specimen from Miocene of Wiesa, Germany for comparison, Senckenberg Museum, SM.B. 21034/I. h–j: Digital transverse sections from micro-CT data of the Holotype V.22953. h: Transverse fracture surface from (b), showing curved locule and zone of weakness defining the germination valve (arrow), reflected light. i: Same orientation with clear demarcation of the separation plane of the germination valve (arrow), digital section from micro-CT scan. j: Enlargement from (h). Scale bars 5mm.