Synchrotron X-ray imaging of a dichasium cupule of Castanopsis from Eocene Baltic amber

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作   者：

Sadowski, Eva-Maria;  Hammel, Joerg U.;  Denk, Thomas; 

作者机构：

Germany;  Dept Palaeobiol;  D-37077 Gottingen;  Swedish Museum Nat Hist;  Dept Geobiol;  Sweden;  Univ Gottingen;  Inst Mat Res;  Max Planck Str 1;  Goldschmidtstr 3;  S-10405 Stockholm;  Helmholtz Zentrum Geesthacht;  Box 50007;  D-21502 Geesthacht; 

关键词：

paleobotany;  paleoecology;  3D reconstruction;  Castanopsis kaulii;  DESY;  evolution;  dichasium cupule;  Fagaceae;  Baltic amber forest; 

期刊名称：

American journal of botany

i s s n：

0002-9122

年卷期：

2018 年 105 卷 12 期

页   码：

2025-2036

页   码：

摘   要：

Premise of the Study The Eocene Baltic amber deposit represents the largest accumulation of fossil resin worldwide, and hundreds of thousands of entrapped arthropods have been recovered. Although Baltic amber preserves delicate plant structures in high fidelity, angiosperms of the "Baltic amber forest" remain poorly studied. We describe a pistillate partial inflorescence of Castanopsis (Fagaceae), expanding the knowledge of Fagaceae diversity from Baltic amber. Methods The amber specimen was investigated using light microscopy and synchrotron-radiation-based X-ray micro-computed tomography (SR mu CT). Key Results The partial inflorescence is a cymule, consisting of an involucre of scales that surround all four pistillate flowers, indicating a dichasium cupule. Subtending bracts are basally covered with peltate trichomes. Flowers possess an urecolate perianth of six nearly free lobes, 12 staminodia hidden by the perianth, and a tri-locular ovary that is convex-triangular in cross section. The exceptional three-dimensional preservation suggests that the fossil belongs to the extant East Asian genus Castanopsis. The amber inclusion represents the first record of Castanopsis from Baltic amber and the first pistillate inflorescence of Fagaceae from Eurasia. Conclusions The partial female inflorescence reported here provides an important addition to acorns of Castanopsis described from middle Eocene strata of Europe. Furthermore, the intercontinental distribution of Castanopsis in the Eocene is confirmed. The amber fossil also broadens the picture of the Baltic amber source area, indicating oligotrophic, sandy, bog-like habitats. Finally, this study underscores the great benefit of SR mu CT as a powerful tool to investigate plant inclusions from amber in a nondestructive way.