This page covers the stem group of the euphyllophyte clade, which comprises the ferns (Subphylum Polypodiophytina, synonymous with Monilophyta) and the seed plants (Spermatophyta).
According to Gerrienne et al (2016), the synapomorphies of the Euphyllophyta are as follows:
The phylogeny of the euphyllophyte stem group has not changed much in articles published over since 2000. A typical example is shown below:
According to Gerrienne et al (2016), the synapomorphies of the Euphyllophyta are as follows:
- Branching pattern either monopodial (stem elongates via new growth produced by a single terminal bud) or pseudomonopodial (results in a plant that looks like it has a dominant ("main") stem and lateral (side) branches, even though branching is really taking place at the apex);
- Helical arrangement of lateral branching systems bearing small, pinnule-like vegetative ultimate appendages;
- Tracheids (long and tapered lignified cells in the xylem of vascular plants) with scalariform (having thickened bands arranged like the rungs of a ladder) bordered pits;
- Sporangia borne in pairs grouped into terminal trusses on lateral branching systems;
- Sporangium dehiscence (splitting or bursting open) through a single slit along one side.
The phylogeny of the euphyllophyte stem group has not changed much in articles published over since 2000. A typical example is shown below:
Figure 2. Time tree of the stem-Euphyllophyta
The oldest known members of the stem euphyllophytes are Eophyllophyton bellum and Psilophyton primitivum, both described from the Early Devonian (Pragian) Posongchong Formation in Wenshan district, Yunnan, China (Hao and Xue, 2013). These are illustrated below, together with the other species shown in the above tree (click on image for a larger view):
Figure 3. Images of stem-Euphyllophyta
The above images are ordered from most basal to most crownward, but there are too few of them to allow evolutionary trends to be suggested.
The euphyllophyte stem line includes a ghost lineage (shown as a blue bar in Figure 1), because the oldest known stem-group lycophyte (of mid-Silurian age; see page on the Lycophyta) is older than the stem-group euphyllophytes, which are of Early Devonian (Pragian) and younger age. Given that the two stem groups must have appeared at the same time, the euphyllophyte stem-group transition must also have begun in the mid-Silurian (Ludlow). Comparing this age with that of the oldest member of the crown euphyllophytes indicates that the stem-to-crown transition lasted around 20 million years, from the mid-Silurian to the Early Devonian (Figure 1).
The euphyllophyte stem line includes a ghost lineage (shown as a blue bar in Figure 1), because the oldest known stem-group lycophyte (of mid-Silurian age; see page on the Lycophyta) is older than the stem-group euphyllophytes, which are of Early Devonian (Pragian) and younger age. Given that the two stem groups must have appeared at the same time, the euphyllophyte stem-group transition must also have begun in the mid-Silurian (Ludlow). Comparing this age with that of the oldest member of the crown euphyllophytes indicates that the stem-to-crown transition lasted around 20 million years, from the mid-Silurian to the Early Devonian (Figure 1).
References
Gerrienne, P., Servais, T., & Vecoli, M. (2016). Plant evolution and terrestrialization during Palaeozoic times—the phylogenetic context. Review of Palaeobotany and Palynology, 227, 4-18.
Hao, S., & Xue, J. (2013). The Early Devonian Posongchong Flora of Yunnan —A Contribution to an Understanding of the Evolution and Early Diversification of Vascular Plants. Science Press, Beijing, 366 pp.
Meyer-Berthaud, B., & Gerrienne, P. (2001). Aarabia, a new Early Devonian vascular plant from Africa (Morocco). Review of Palaeobotany and Palynology, 116(1-2), 39-53.
Hao, S., & Xue, J. (2013). The Early Devonian Posongchong Flora of Yunnan —A Contribution to an Understanding of the Evolution and Early Diversification of Vascular Plants. Science Press, Beijing, 366 pp.
Meyer-Berthaud, B., & Gerrienne, P. (2001). Aarabia, a new Early Devonian vascular plant from Africa (Morocco). Review of Palaeobotany and Palynology, 116(1-2), 39-53.
Image credits – stem-Euphyllophyta
- Figure 2 (Aarabia brevicaulis): Falconaumanni, CC BY-SA 3.0 <https://creativecommons.org/licenses/by-sa/3.0>, via Wikimedia Commons
- Figure 2 (Eophyllophyton bellum, fossil images): Open Access article Hao, S., & Xue, J. (2013). Earliest record of megaphylls and leafy structures, and their initial diversification. Chinese Science Bulletin, 58, 2784-2793.
- Figure 2 (Eophyllophyton bellum, life restoration): Open Access article Hao, S., & Xue, J. (2013). Earliest record of megaphylls and leafy structures, and their initial diversification. Chinese Science Bulletin, 58, 2784-2793.
- Figure 2 (Psilophyton primitivum): Open Access article Capel, E., Cleal, C. J., Xue, J., Monnet, C., Servais, T., & Cascales-Miñana, B. (2022). The Silurian–Devonian terrestrial revolution: diversity patterns and sampling bias of the vascular plant macrofossil record. Earth-Science Reviews, 231, 104085.
- Figure 2 (Psilophyton dawsonii, fossil): Ghedoghedo, CC BY-SA 3.0 <https://creativecommons.org/licenses/by-sa/3.0>, via Wikimedia Commons
- Figure 2 (Psilophyton dawsonii, life restoration): Open Access article Hao, S., & Xue, J. (2013). Earliest record of megaphylls and leafy structures, and their initial diversification. Chinese Science Bulletin, 58, 2784-2793.