An interpretation of the phylogeny of the stem-Spermatophyta, based on two publications, is shown in the time tree below:
Figure 1. Time tree of the stem-Spermatophyta
The oldest known member of the seed plant stem group is Aneurophyton germanicum, described from Middle Devonian (Late Eifelian) sediments in the Massif de la Vesdre at Goé, Belgium (Momont et al, 2012; Toledo et al, 2021). This species is illustrated below, together with other stem group fossils for which images are available in the public domain (click on image for a larger view):
Figure 2. Images of stem-Spermatophyta
The above images are ordered from most basal to most crownward, and it seems possible to suggest tentatively that there is a trend from primitive-looking trees such as Aneurophyton through Tetraxylopteris to trees that look somewhat more like those of the present day (Archaeopteris).
References
Hilton, J., & Bateman, R. M. (2006). Pteridosperms are the backbone of seed-plant phylogeny. The Journal of the Torrey Botanical Society, 133(1), 119-168.
Momont, N., Gerrienne, P., & Prestianni, C. (2012). Aneurophyton germanicum (Aneurophytales-Progymnosperms) from the Middle Devonian of Belgium and Germany. Japanese Journal of Palynology, 58 (Special), 156-157.
Toledo, S., Bippus, A. C., Atkinson, B. A., Bronson, A. W., & Tomescu, A. M. (2021). Taxon sampling and alternative hypotheses of relationships in the euphyllophyte plexus that gave rise to seed plants: insights from an Early Devonian radiatopsid. New Phytologist, 232(2), 914-927.
Momont, N., Gerrienne, P., & Prestianni, C. (2012). Aneurophyton germanicum (Aneurophytales-Progymnosperms) from the Middle Devonian of Belgium and Germany. Japanese Journal of Palynology, 58 (Special), 156-157.
Toledo, S., Bippus, A. C., Atkinson, B. A., Bronson, A. W., & Tomescu, A. M. (2021). Taxon sampling and alternative hypotheses of relationships in the euphyllophyte plexus that gave rise to seed plants: insights from an Early Devonian radiatopsid. New Phytologist, 232(2), 914-927.
Image credits – stem-Spermatophyta
- Figure 2 (Rellimia sp.): From Open Access article Harrison, C. J., & Morris, J. L. (2018). The origin and early evolution of vascular plant shoots and leaves. Philosophical Transactions of the Royal Society B: Biological Sciences, 373(1739), 20160496.
- Figure 2 (Aneurophyton germanicum, fossil): Ghedoghedo, CC BY-SA 4.0 <https://creativecommons.org/licenses/by-sa/4.0>, via Wikimedia Commons
- Figure 2 (Aneurophyton germanicum, life restoration): Ghedoghedo, CC BY-SA 3.0 <https://creativecommons.org/licenses/by-sa/3.0>, via Wikimedia Commons
- Figure 2 (Tetraxylopteris sp., fossil): Skye McDavid, CC BY 4.0 <https://creativecommons.org/licenses/by/4.0>, via Wikimedia Commons
- Figure 2 (Tetraxylopteris sp., life restoration): Falconaumanni, CC BY-SA 3.0 <https://creativecommons.org/licenses/by-sa/3.0>, via Wikimedia Commons
- Figure 2 (Archaeopteris macilenta, fossil): Photographed by Bob James (owner of website) at Denver Museum of Nature & Science, August 2023.
- Figure 2 (Archaeopteris macilenta, life restoration): Retallack, CC BY-SA 4.0 <https://creativecommons.org/licenses/by-sa/4.0>, via Wikimedia Commons
- Figure 2 (Elkinsia sp.): Zeiram1990 aka Georgi Ivanov on Fandom under CC BY-SA license
- Figure 2 (Heterangium americanum): Photo by John Hall, Botanical Society of America, licensed under a Creative Commons Attribution-NonCommercial-ShareAlike 3.0 Unported License.
- Figure 2 (Lyginopteris baeumleri): Daderot, CC0, via Wikimedia Commons
- Figure 2 (Medullosa stellata): Ghedoghedo, CC BY-SA 4.0 <https://creativecommons.org/licenses/by-sa/4.0>, via Wikimedia Commons