Skip to main page content
U.S. flag

An official website of the United States government

Dot gov

The .gov means it’s official.
Federal government websites often end in .gov or .mil. Before sharing sensitive information, make sure you’re on a federal government site.

Https

The site is secure.
The https:// ensures that you are connecting to the official website and that any information you provide is encrypted and transmitted securely.

Access keys NCBI Homepage MyNCBI Homepage Main Content Main Navigation
. 2013 Mar 27:13:72.
doi: 10.1186/1471-2148-13-72.

Chengia laxispicata gen. et sp. nov., a new ephedroid plant from the Early Cretaceous Yixian Formation of western Liaoning, Northeast China: evolutionary, taxonomic, and biogeographic implications

Yong Yang  1 , Longbiao Lin, Qi Wang
Affiliations

Chengia laxispicata gen. et sp. nov., a new ephedroid plant from the Early Cretaceous Yixian Formation of western Liaoning, Northeast China: evolutionary, taxonomic, and biogeographic implications

Yong Yang et al. BMC Evol Biol. .

Abstract

Background: The extant Gnetales include three monotypic families, namely, Ephedraceae (Ephedra), Gnetaceae (Gnetum), and Welwitschiaceae (Welwitschia), all of which possess compound female cones that comprise a main axis and 1 to multiple pairs/whorls of bracts subtending a female reproductive unit or having lower pairs/whorls of bracts sterile. However, the evolutionary origin of such a reproductive architecture in Gnetales is controversial in the light of the competing anthophyte versus gnetifer hypotheses of seed plant relationships. Hence, macrofossils demonstrating the structure of compound female cones of the Gnetales should be important to decipher the early evolution of the order.

Results: A new ephedroid plant Chengia laxispicata gen. et sp. nov. is described from the Early Cretaceous Yixian Formation of western Liaoning, Northeast China. The fossil represents a part of a leafy shooting system with reproductive organs attached. The main shoot bears internodes and swollen nodes, from which lateral branches arise oppositely. Reproductive organs consist of female spikes terminal to twigs or axillary to linear leaves. Spikes are loosely arranged, having prominent nodes and internodes. Bracts of the spikes are decussately opposite and comprise 4-8 pairs of bracts. Each bract subtends an ellipsoid seed. Seeds are sessile, with a thin outer envelope and a distal micropylar tube.

Conclusions: Chengia laxispicata gen. et sp. nov. provides a missing link between archetypal fertile organs in the crown lineage of the Gnetales and compound female cones of the extant Ephedraceae. Combined with a wealth of Ephedra and ephedroid macrofossils from the Early Cretaceous, we propose a reduction and sterilization hypothesis that the female cone of the extant Ephedraceae may have stemmed from archetypal fertile organs in the crown lineage of the Gnetales. These have undergone sequentially intermediate links similar to female cones of Cretaceous Siphonospermum, Chengia, and Liaoxia by reduction and sterilization of the lower fertile bracts, shortenings of internodes and peduncles as well as loss of reproductive units in all inferior bracts. The basal family Ephedraceae including Ephedra of the extant Gnetales was demonstrated to have considerable diversity by the Early Cretaceous, so an emended familial diagnosis is given here. The Jehol Biota in Northeast China and adjacent areas contains a plethora of well-preserved macrofossils of Ephedra and ephedroids that show different evolutionary stages including primitive and derived characters of Ephedraceae, so Northeast China and adjacent areas may represent either the centre of origination or one of the centres for early diversification of the family.

PubMed Disclaimer

Figures

Figure 1
Figure 1
Three extant genera and phylogenetic relationships of the Gnetales. (a) Ephedra minuta Florin photographed at Chayu, Xizang (Tibet), China. (b) Gnetum parvifolium (Warb.) C.Y. Cheng ex Chun photographed at Fairy Lake Botanic Garden, Shenzhen, Guangdong Province, China. (c) Welwitschia mirabilis Hook. f. photographed at Dahlem Botanic Garden, Berlin, Germany. (d) Simplified phylogenetic trees of the Gnetales within seed plants (after [14]). Left: Gnetales are placed at the base of an anthophyte clade in the morphology tree. Right: Gnetales are embedded within conifers forming a gnetifer clade in the molecular tree.
Figure 2
Figure 2
The general morphology of Chengia laxispicata gen. et sp. nov.. Holotype: PE 2012041619A, B. A gathering of part (a) and counterpart (b) specimens. Note that there is a piece of Lycoptera fish fossil exposed on the bedding plane below this plant-bearing bed.
Figure 3
Figure 3
Morphological detail of Chengia laxispicata gen. et sp. nov.. (a) A node showing the opposite branching pattern and subtending elongate-linear leaf (arrows). (b) An internode showing the fine longitudinal striations. (c) Terminal female spikes with the loosely arranged bracts and prominent internodes. (d–e) The morphology of female reproductive units. Green arrows refer to an enveloped seed axillary to a bract. White arrows refer to a thin, hollow micropylar tube. (f–g) The camera lucida drawing of partial spikes in (e) and (d), showing the decussate and opposite fertile bracts.
Figure 4
Figure 4
A reconstruction of Chengia laxispicata gen. et sp. nov.. (a) The general morphology of Chengia laxispicata. (b) The morphology of a partial female reproductive spike.
Figure 5
Figure 5
A reduction and sterilization hypothesis on the evolutionary pathways of female cones of Ephedraceae. (a) A hypothesized archetypal fertile organs of the crown lineage of the Gnetales. (b) Female reproductive units directly terminal to peduncles and bearing no supporting bracts like ephedroid macrofossil Siphonospermum simplex Rydin et Friis [77]. (c) A loosely arranged female cone having multiple pairs of fertile bracts like ephedroid macrofossil Chengia laxispicata gen. et sp. nov. presented herein (Figure 2a–b). (d) A compact female cone bearing multiple whorls of fertile bracts like ephedroid macrofossil Liaoxia robusta Rydin et al. [74]. (e) Reduced tri-ovulate, bi-ovulate, and uni-ovulate female cones bearing only one whorl/pair of fertile bracts like ephedroid macrofossils Ephedra carnosa Yang et Wang [61], E. archaeorhytidosperma Yang et al. [62], E. hongtaoi Wang et Zheng [63], and Gurvanella exquisita Sun et al. and G. dictyoptera Krassilov [67-69]. (f) Reduced and compact female cones of modern Ephedra species bearing only the terminal bract or the uppermost pair/whorl of bracts fertile and the inferior bracts sterile [4,6,7,9].
Figure 6
Figure 6
The geographic positions of ephedroid macrofossil localities in western Liaoning Province, Northeast China. Left: Dawangzhangzi Village, Lingyuan City—the type locality of Chengia laxispicata gen. et sp. nov.. Middle: Huangbanjigou Village, Beipiao City—a previously reported locality abundant in ephedroid macrofossils.
See this image and copyright information in PMC

References

    1. Arber EAN, Parkin J. Studies on the evolution of the angiosperms, the relationship of the angiosperms to the Gnetales. Ann Bot. 1908;22:489–515.
    1. Mehra PN. Occurrence of hermaphrodite flowers and the development of the female gametophyte in Ephedra intermedia Schrenk et Mey. Ann Bot. 1950;14:165–180.
    1. Endress PK. Structures and function of female and bisexual organ complexes in Gnetales. Int J Plant Sci. 1996;157(6 suppl.):S113–S125.
    1. Yang Y. Systematics and evolution of Ephedra L. (Ephedraceae) from China. Beijing: Institute of Botany, Chinese Academy of Sciences; 2002. (Ph.D. thesis).
    1. Muhammad AF, Sattler R. Vessel structure of Gnetum and the origin of angiosperms. Am J Bot. 1982;69:1004–1021. doi: 10.2307/2442898. - DOI

Publication types

LinkOut - more resources