The angiosperms represent the sister clade to the gymnosperms (Scutt, 2021). They differ from the gymnosperms in that the ovule (egg) is fertilized and develops into a seed in an enclosed hollow ovary (Encyclopaedia Britannica). In gymnosperms the ovule is exposed. Angiosperms, which comprise the largest and most diverse group within the plant kingdom, are now classified into 64 orders (Zuntini et al, 2024).
There is no consensus as to which fossils, if any, belong to the angiosperm stem line (Doyle, 2018; Bateman, 2020; Coiro et al, 2020; Benton et al, 2022). This problem is one manifestation of Darwin’s statement in 1879 that “The rapid development as far as we can judge of all the higher plants within recent geological times is an abominable mystery” (quoted in Friedman, 2009). Even though Darwin’s “abominable mystery” applied not to the origin of the angiosperms but to their rapid diversification during the Early Cretaceous (Friedman, 2009), the phrase has commonly been used to express the continuing difficulty of tracing the origin of the flowering plants in the fossil record (Bateman, 2020).
The phylogeny of the angiosperm crown group is still unstable (Li et al, 2021; Guo et al, 2021; Zuntini et al, 2024). Furthermore, studies with fossil calibrations of molecular clock of clade ages (e.g. Magallón et al, 2015; Barba‐Montoya et al, 2018; Li et al, 2019) mention very few stem-group fossils that have been unequivocally defined for the constituent orders and higher clades within the angiosperms.
In view of these issues, very little useful information is available at present (September, 2024) to document transitional fossils either on the stem line of the angiosperms or within the angiosperm crown group.
However, recent research, primarily by Chinese paleobotanists, has allowed the age of the angiosperm total group to be extended as far back as the Early or Middle Jurassic (Wang, 2023). These findings have been disputed by many western researchers (e.g. Bateman, 2020), but a recent article in Nature (Fu et al, 2023) has demonstrated clearly that the oldest known pre-Cretaceous species, Nanjinganthus dendrostyla, has ovules enclosed within its ovaries and is thus undeniably an angiosperm.
None of these pre-Cretaceous angiosperms have been analyzed phylogenetically to define their relationship to each other or to the crown group. This implies that we can only classify them as members of the angiosperm total group; as yet we do not know whether they belong to the crown group or the stem group.
A number of these total-group angiosperms are illustrated below, together with the oldest known member of the angiosperm crown group, Montsechia vidalii. This plant was described from the Pedrera de Rubiés Formation, of Early Cretaceous (Early Barremian) age, at the La Pedrera and La Cabroa localities in the Montsec chain, Lleida Province, Catalonia, Spain Gomez et al, 2020; Zuntini et al, 2024). (Click on image for a larger view):
There is no consensus as to which fossils, if any, belong to the angiosperm stem line (Doyle, 2018; Bateman, 2020; Coiro et al, 2020; Benton et al, 2022). This problem is one manifestation of Darwin’s statement in 1879 that “The rapid development as far as we can judge of all the higher plants within recent geological times is an abominable mystery” (quoted in Friedman, 2009). Even though Darwin’s “abominable mystery” applied not to the origin of the angiosperms but to their rapid diversification during the Early Cretaceous (Friedman, 2009), the phrase has commonly been used to express the continuing difficulty of tracing the origin of the flowering plants in the fossil record (Bateman, 2020).
The phylogeny of the angiosperm crown group is still unstable (Li et al, 2021; Guo et al, 2021; Zuntini et al, 2024). Furthermore, studies with fossil calibrations of molecular clock of clade ages (e.g. Magallón et al, 2015; Barba‐Montoya et al, 2018; Li et al, 2019) mention very few stem-group fossils that have been unequivocally defined for the constituent orders and higher clades within the angiosperms.
In view of these issues, very little useful information is available at present (September, 2024) to document transitional fossils either on the stem line of the angiosperms or within the angiosperm crown group.
However, recent research, primarily by Chinese paleobotanists, has allowed the age of the angiosperm total group to be extended as far back as the Early or Middle Jurassic (Wang, 2023). These findings have been disputed by many western researchers (e.g. Bateman, 2020), but a recent article in Nature (Fu et al, 2023) has demonstrated clearly that the oldest known pre-Cretaceous species, Nanjinganthus dendrostyla, has ovules enclosed within its ovaries and is thus undeniably an angiosperm.
None of these pre-Cretaceous angiosperms have been analyzed phylogenetically to define their relationship to each other or to the crown group. This implies that we can only classify them as members of the angiosperm total group; as yet we do not know whether they belong to the crown group or the stem group.
A number of these total-group angiosperms are illustrated below, together with the oldest known member of the angiosperm crown group, Montsechia vidalii. This plant was described from the Pedrera de Rubiés Formation, of Early Cretaceous (Early Barremian) age, at the La Pedrera and La Cabroa localities in the Montsec chain, Lleida Province, Catalonia, Spain Gomez et al, 2020; Zuntini et al, 2024). (Click on image for a larger view):
Figure 1: Images of early total-group angiosperms
References
Bateman, R. M. (2020). Hunting the Snark: the flawed search for mythical Jurassic angiosperms. Journal of Experimental Botany, 71(1), 22-35.
Fu, Q., Hou, Y., Yin, P., Diez, J. B., Pole, M., García-Ávila, M., & Wang, X. (2023). Micro-CT results exhibit ovules enclosed in the ovaries of Nanjinganthus. Scientific Reports, 13(1), 426.
Gomez, B., Daviero‐Gomez, V., Coiffard, C., Barral, A., Martín‐Closas, C., & Dilcher, D. L. (2020). Montsechia vidalii from the Barremian of Spain, the earliest known submerged aquatic angiosperm, and its systematic relationship to Ceratophyllum. Taxon, 69(6), 1273-1292.
Scutt, C. P. (2021). The origin of angiosperms. In Evolutionary developmental biology: a reference guide (pp. 663-682). Cham: Springer International Publishing.
Wang, X. (2023). Origin of Angiosperms: Problems, Challenges, and Solutions. Life, 13(10), 2029.
Zuntini, A. R., Carruthers, T., Maurin, O., Bailey, P. C., Leempoel, K., Brewer, G. E., ... & Knapp, S. (2024). Phylogenomics and the rise of the angiosperms. Nature 629, 843–850.
Fu, Q., Hou, Y., Yin, P., Diez, J. B., Pole, M., García-Ávila, M., & Wang, X. (2023). Micro-CT results exhibit ovules enclosed in the ovaries of Nanjinganthus. Scientific Reports, 13(1), 426.
Gomez, B., Daviero‐Gomez, V., Coiffard, C., Barral, A., Martín‐Closas, C., & Dilcher, D. L. (2020). Montsechia vidalii from the Barremian of Spain, the earliest known submerged aquatic angiosperm, and its systematic relationship to Ceratophyllum. Taxon, 69(6), 1273-1292.
Scutt, C. P. (2021). The origin of angiosperms. In Evolutionary developmental biology: a reference guide (pp. 663-682). Cham: Springer International Publishing.
Wang, X. (2023). Origin of Angiosperms: Problems, Challenges, and Solutions. Life, 13(10), 2029.
Zuntini, A. R., Carruthers, T., Maurin, O., Bailey, P. C., Leempoel, K., Brewer, G. E., ... & Knapp, S. (2024). Phylogenomics and the rise of the angiosperms. Nature 629, 843–850.
Image credits – Origin of Angiosperms
- Header (Texas Bluebonnets just south of Dallas, TX. March, 2012): Jeffrey Pang, CC BY 2.0 <https://creativecommons.org/licenses/by/2.0>, via Wikimedia Commons
- Figure 1 (Nanjinganthus dendrostyla, two fossil images): Open Access article Fu, Q., Hou, Y., Yin, P., Diez, J. B., Pole, M., García-Ávila, M., & Wang, X. (2023). Micro-CT results exhibit ovules enclosed in the ovaries of Nanjinganthus. Scientific Reports, 13(1), 426.
- Figure 1 (Nanjinganthus dendrostyla, life restoration): Open Access article Fu, Q., Hou, Y., Yin, P., Diez, J. B., Pole, M., García-Ávila, M., & Wang, X. (2023). Micro-CT results exhibit ovules enclosed in the ovaries of Nanjinganthus. Scientific Reports, 13(1), 426.
- Figure 1 (Qingganninginfructus formosa): Open Access article Han, L., Zhao, Y., Zhao, M., Sun, J., Sun, B., & Wang, X. (2023). New Fossil Evidence Suggests That Angiosperms Flourished in the Middle Jurassic. Life, 13(3), 819.
- Figure 1 (Xenofructus dabuensis): Open Access article Fu, Q., Sun, J., Zheng, S., & Wang, X. (2024). Unique Jurassic Ovaries Shed a New Light on the Nature of Carpels. Plants, 13(16), 2239.
- Figure 1 (Euanthus panii, fossil): Open Access article Liu, Z. J., & Wang, X. (2016). A perfect flower from the Jurassic of China. Historical Biology, 28(5), 707-719.
- Figure 1 (Euanthus panii, life restoration): Open Access article Liu, Z. J., & Wang, X. (2016). A perfect flower from the Jurassic of China. Historical Biology, 28(5), 707-719.
- Figure 1 (Florigerminis jurassica): Open Access article Cui, D. F., Hou, Y., Yin, P., & Wang, X. (2022). A Jurassic flower bud from China.From Chang, S.-C. and Zheng, D. (eds) 2022. Mesozoic Biological Events and Ecosystems in East Asia. Geological Society, London, Special Publications, 521, 81–93.
- Figure 1 (Daohugoufructus sinensis, fossil): Open Access article 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.
- Figure 1 (Daohugoufructus sinensis, life restoration): Open Access article 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.
- Figure 1 (Montsechia vidalii): Eduard Monera, CC BY-SA 4.0 <https://creativecommons.org/licenses/by-sa/4.0>, via Wikimedia Commons