Friday, May 29, 2015

[PaleoBotany • 2015] Euanthus panii • A Perfect Flower from the Jurassic of China



Flower, enclosed ovule and tetrasporangiate anther are three major characters distinguishing angiosperms from other seed plants. Morphologically, typical flowers are characterised by an organisation with gynoecium and androecium surrounded by corolla and calyx. Theoretically, flowers are derived from their counterparts in ancient ancestral gymnosperms. However, as for when, how and from which groups, there is no consensus among botanists yet. Although angiosperm-like pollen and angiosperms have been claimed in the Triassic and Jurassic, typical flowers with the aforesaid three key characters are still missing in the pre-Cretaceous age, making many interpretations of flower evolution tentative. Thus searching for flower in the pre-Cretaceous has been a tantalising task for palaeobotanists for a long time. Here, we report a typical flower, Euanthus panii gen. et sp. nov., from the Middle –Late Jurassic of Liaoning, China. Euanthus has sepals, petals, androecium with tetrasporangiate dithecate anthers and gynoecium with enclosed ovules, organised just like in perfect flowers of extant angiosperms. The discovery of Euanthus implies that typical angiosperm flowers have already been in place in the Jurassic, and provides a new insight unavailable otherwise for the evolution of flowers. 

Keywords: flower; angiosperm; Jurassic; China; Liaoning



Figure 8. Sketch, details of micropyle and reconstruction of Euanthus panii gen. et sp. nov.
(a) Sketch of the specimen shown in Figure 4(a). (b) Sketch of the micropyle, nucellus (N), and integument (blue) shown in Figure 7(j). (c) Reconstruction of Euanthus panii gen. et sp. nov.

Figure 4. Euanthus panii gen. et sp. nov. and its details. Stereomicroscopy.
 (a, b) The flower in two facing parts, with sepals (S) and petals (P) radiating from the receptacle. The black arrows mark the distal of the style, and the blue arrow in (b) marks the stamen shown in Figure 6 (d),(e),(h). Holotype: PB21685, PB21684. Bar ¼ 5 mm. (c) A sepal (S) is almost structureless between the two arrows, implying that it is attached to the receptacle (O) with its whole base. Enlarged from (a). Bar ¼ 1 mm. (d) Pentamerous receptacle with ovarian cavity (O) in its centre. Note the corners (arrows) of about 1108. Bar ¼ 0.5 mm. (e) Basal portion of the flower after degagement. Note spatial relationship among the ovary (O), style base, a possible filament stub (arrow), sepals (S) and petal (P). Refer to Figure 7(f). Bar ¼ 1 mm.

Type species: Euanthus panii gen. et sp. nov. 

Etymology: Euanthus, for real flower in Latin. 

Horizon: the Jiulongshan Formation. 
Locality: Sanjiaocheng Village, Huloudao City, Liaoning, China

Figure 8. Sketch, details of micropyle and reconstruction of Euanthus panii gen. et sp. nov. (a) Sketch of the specimen shown in Figure 4(a). (b) Sketch of the micropyle, nucellus (N), and integument (blue) shown in Figure 7(j). (c) Reconstruction of Euanthus panii gen. et sp. nov.


Conclusion 
Euanthus from the Middle–Late Jurassic of Liaoning, China is a perfect flower typical of angiosperms, prompting a rethinking on the origin and history of flowers and angiosperms. If Euanthus were really related to eudicots, it would be intriguing to search for typical eudicot leaves in the Jurassic strata. The presence of a full-fledged flower such as Euanthus in the Jurassic is apparently out of the expectations of any currently accepted evolutionary theories, implying either that these theories are flawed, and/or the history of angiosperms is much longer than previously assumed.


 Zhong-Jian Liu and Xin Wang. 2015. A Perfect Flower from the Jurassic of China.
Historical Biology: An International Journal of Paleobiology.

DOI: 10.1080/08912963.2015.1020423

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