This page covers the stem groups of the three orders (Ephedrales, Welwitschiales and Gnetales) of which the subclass Gnetidae is composed. Examples of these orders are shown in the above header photographs, which illustrate the major morphological differences between them.
The phylogeny of the crown group, based on work by Yang et al (2023), is illustrated in the time tree below:
The phylogeny of the crown group, based on work by Yang et al (2023), is illustrated in the time tree below:
Figure 1. Summarized phylogenetic tree of the crown-Gnetidae
The above tree indicates that the stem-group fossils of the three orders all appeared during the Early Cretaceous. However, no younger stem-group fossils are known, and the crown groups comprise only extant species. There is thus a long period of time for which the stem-crown transitions are undocumented in the fossil record (see discussions in Yang et al, 2015 and Coiro et al, 2022).
As implied by Figure 1, no fossils have yet been assigned to the stem group of the clade comprising the Gnetales and the Welwitschiales.
The oldest known members of the stem-Ephedrales are all of Early Cretaceous (Late Barremian - Early Aptian) age. The species with the best images available in the public domain is the stem-Ephedrales member Chengia laxispicata, described from the lower part of the Yixian Formation at Dawangzhangzi Village, Songzhangzi Town, Lingyuan City, Chaoyang District, Liaoning Province, China (Yang et al, 2013; 2023). This species is illustrated below, together with other fossils for which images are available in the public domain (click on image for larger view):
As implied by Figure 1, no fossils have yet been assigned to the stem group of the clade comprising the Gnetales and the Welwitschiales.
The oldest known members of the stem-Ephedrales are all of Early Cretaceous (Late Barremian - Early Aptian) age. The species with the best images available in the public domain is the stem-Ephedrales member Chengia laxispicata, described from the lower part of the Yixian Formation at Dawangzhangzi Village, Songzhangzi Town, Lingyuan City, Chaoyang District, Liaoning Province, China (Yang et al, 2013; 2023). This species is illustrated below, together with other fossils for which images are available in the public domain (click on image for larger view):
Figure 2. Images of stem-Ephedrales
Clearly there are not enough images to discern any trends in the stem group.
Turning to the Welwitschiales, only two species were recognized as members of the stem group by Yang et al (2023), as shown in Figure 1 above. The only one with an image available in the public domain is the oldest of the two, Welwitschiostrobus murili, described from the Early Cretaceous (Late Aptian) Crato Formation at Chapada do Araripe in northeastern Brazil (Dilcher et al, 2005). An image of stems and cones of this species is shown below:
Turning to the Welwitschiales, only two species were recognized as members of the stem group by Yang et al (2023), as shown in Figure 1 above. The only one with an image available in the public domain is the oldest of the two, Welwitschiostrobus murili, described from the Early Cretaceous (Late Aptian) Crato Formation at Chapada do Araripe in northeastern Brazil (Dilcher et al, 2005). An image of stems and cones of this species is shown below:
Figure 3. Image of a member of the stem-Welwitschiales
With respect to the Gnetales, only one species, Khitania columnispicata, was assigned by Yang et al (2023) to the stem group (see Figure 1). This fossil was found in the Early Cretaceous (Late Barremian - Early Aptian) Yixian Formation near the villages of Huangbanjigou and Jianshangou in Beipiao, Liaoning, northeastern China (Guo et al, 2009). Again, no image is available in the public domain.
The time scale on Figure 1 implies that the stem-to-crown transition was very long for all three orders (at least 107 million years), from the Early Cretaceous to the present day. However, given that molecular clock studies have indicated that the crown group of the Gnetales might have appeared from the Late Cretaceous to the Eocene and that of the Ephedrales from the Oligocene to the Miocene (Table 4 of Yang et al, 2017), it is highly probable that currently unknown crown-group fossils will be found in the future. Such fossils could substantially shorten the stem-crown transition period.
The time scale on Figure 1 implies that the stem-to-crown transition was very long for all three orders (at least 107 million years), from the Early Cretaceous to the present day. However, given that molecular clock studies have indicated that the crown group of the Gnetales might have appeared from the Late Cretaceous to the Eocene and that of the Ephedrales from the Oligocene to the Miocene (Table 4 of Yang et al, 2017), it is highly probable that currently unknown crown-group fossils will be found in the future. Such fossils could substantially shorten the stem-crown transition period.
References
Coiro, M., Roberts, E. A., Hofmann, C. C., & Seyfullah, L. J. (2022). Cutting the long branches: Consilience as a path to unearth the evolutionary history of Gnetales. Frontiers in Ecology and Evolution, 10, 1082639.
Dilcher, D. L., Bernardes‐De‐Oliveira, M. E., Pons, D., & Lott, T. A. (2005). Welwitschiaceae from the Lower Cretaceous of northeastern Brazil. American Journal of Botany, 92(8), 1294-1310.
Doyle, J. A. (2006). Seed ferns and the origin of angiosperms. The Journal of the Torrey Botanical Society, 133(1), 169-209.
Guo, S. X., Sha, J. G., Bian, L. Z., & Qiu, Y. L. (2009). Male spike strobiles with Gnetum affinity from the Early Cretaceous in western Liaoning, Northeast China. Journal of Systematics and Evolution, 47(2), 93-102.
Yang, Y., Lin, L., & Wang, Q. (2013). 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. BMC Evolutionary Biology, 13, 1-13.
Yang, Y., Lin, L., & Ferguson, D. K. (2015). Parallel evolution of leaf morphology in gnetophytes. Organisms Diversity & Evolution, 15, 651-662.
Yang, Y., Xie, L., & Ferguson, D. K. (2017). Protognetaceae: A new gnetoid macrofossil family from the Jurassic of northeastern China. Perspectives in Plant Ecology, Evolution and Systematics, 28, 67-77.
Yang, Y., Yang, Z., Lin, L., Wang, Y., & Ferguson, D. K. (2023). A New Gnetalean Macrofossil from the Mid-Jurassic Daohugou Formation. Plants, 12(9), 1749.
Dilcher, D. L., Bernardes‐De‐Oliveira, M. E., Pons, D., & Lott, T. A. (2005). Welwitschiaceae from the Lower Cretaceous of northeastern Brazil. American Journal of Botany, 92(8), 1294-1310.
Doyle, J. A. (2006). Seed ferns and the origin of angiosperms. The Journal of the Torrey Botanical Society, 133(1), 169-209.
Guo, S. X., Sha, J. G., Bian, L. Z., & Qiu, Y. L. (2009). Male spike strobiles with Gnetum affinity from the Early Cretaceous in western Liaoning, Northeast China. Journal of Systematics and Evolution, 47(2), 93-102.
Yang, Y., Lin, L., & Wang, Q. (2013). 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. BMC Evolutionary Biology, 13, 1-13.
Yang, Y., Lin, L., & Ferguson, D. K. (2015). Parallel evolution of leaf morphology in gnetophytes. Organisms Diversity & Evolution, 15, 651-662.
Yang, Y., Xie, L., & Ferguson, D. K. (2017). Protognetaceae: A new gnetoid macrofossil family from the Jurassic of northeastern China. Perspectives in Plant Ecology, Evolution and Systematics, 28, 67-77.
Yang, Y., Yang, Z., Lin, L., Wang, Y., & Ferguson, D. K. (2023). A New Gnetalean Macrofossil from the Mid-Jurassic Daohugou Formation. Plants, 12(9), 1749.
Image credits – crown-Gnetidae
- Header (Ephedrales: Ephedra viridis in Red Rock Canyon, Nevada): Stan Shebs, under Creative Commons Attribution-Share Alike 3.0 Unported license
- Header (Welwitschiales: Welwitchia mirabilis, male plant, Namibia): Luxil, CC BY-SA 3.0 <https://creativecommons.org/licenses/by-sa/3.0>, via Wikimedia Commons
- Header (Gnetales: Gnetum gnemon): Ko Ko Maung, licensed under a Creative Commons Attribution-Noncommercial 3.0 License
- Figure 2 (Chengia laxispicata, fossil): From Open Access article Yang, Y., Lin, L., & Wang, Q. (2013). 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. BMC Evolutionary Biology, 13, 1-13.
- Figure 2 (Chengia laxispicata, life restoration): From Open Access article Yang, Y., Lin, L., & Wang, Q. (2013). 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. BMC Evolutionary Biology, 13, 1-13.
- Figure 2 (Beipiaoa spinosa): Open Access article Yang, Y., Wang, Y., & Ferguson, D. K. (2020). A new macrofossil ephedroid plant with unusual bract morphology from the Lower Cretaceous Jiufotang Formation of northeastern China. BMC Evolutionary Biology, 20(1), 1-12.
- Figure 2 (Gurvanella dictyopteran): Open Access article Yang, Y., Wang, Y., & Ferguson, D. K. (2020). A new macrofossil ephedroid plant with unusual bract morphology from the Lower Cretaceous Jiufotang Formation of northeastern China. BMC Evolutionary Biology, 20(1), 1-12.
- Figure 3: (Welwitschiostrobus murili): UNIVERSIDADE DE SÃO PAULO, Foto: Marcos Santos/USP Imagens