Progymnosperm
Extinct woody plants ancestral to seed plants and first trees.
Progymnosperms were woody, spore-producing plants that no longer exist. They are thought to have come from the trimerophytes and later developed into the spermatophytes, which are the ancestors of both gymnosperms and flowering plants (angiosperms). In formal classification, they have been placed either as the division Progymnospermophyta or the class Progymnospermopsida. These plants form a paraphyletic grade.
The oldest known progymnosperms come from the Middle Devonian, in the order Aneurophytales. Early forms like *Protopteridium* had loose clusters of axes for vegetative organs, while *Tetraxylopteris* lacked leaves entirely. Later aneurophytaleans, such as *Aneurophyton*, developed vegetative organs that looked more like fronds. By the Late Devonian, the Aneurophytales are thought to have given rise to the pteridosperm order Lyginopteridales. Also in the Late Devonian, another group of progymnosperms produced the first truly large trees, known as *Archaeopteris*. The last surviving progymnosperms were the Noeggerathiales, which lived until the end of the Permian.
Other features include a vascular cambium with unlimited growth potential, along with xylem and phloem. These plants were ancestors of the earliest seed plants and the first true trees. They showed strong monopodial growth. The Aneurophytales were homosporous, while the other groups were heterosporous. Both the Archaeopteridales and Noeggerathiales had pycnoxylic wood.
- classification
- Extinct group of woody, spore-bearing plants
- stratigraphic_range
- Middle Devonian to end of Permian
- earliest_known_order
- Aneurophytales (Middle Devonian)
- latest_surviving_group
- Noeggerathiales (until end of Permian)
- key_characteristics
- Vascular cambium with unlimited growth potential; xylem and phloem; strong monopodial growth; pycnoxylic wood in Archaeopteridales and Noeggerathiales
- spore_type
- Aneurophytales homosporous; remaining groups heterosporous
Lore & Background
Progymnosperms were an extinct group of woody, spore-bearing plants that are considered ancestral to both gymnosperms and angiosperms. Their appearance varied across subgroups. The earliest known forms, from the Middle Devonian order Aneurophytales, lacked true leaves and consisted of loose clusters of axes; for example, *Protopteridium* had such a structure, while *Tetraxylopteris* was also leafless. In more advanced aneurophytaleans like *Aneurophyton*, the vegetative organs began to resemble fronds. Later, during the Late Devonian, another lineage gave rise to *Archaeopteris*, which represents the first truly large trees. The latest surviving group, the Noeggerathiales, persisted until the end of the Permian. Defining characteristics include the presence of a vascular cambium with unlimited growth potential, producing both xylem and phloem, and strong monopodial growth. The Aneurophytales were homosporous, while later groups were heterosporous. Pycnoxylic wood, a dense type of wood, was present in both the Archaeopteridales and Noeggerathiales. Progymnosperms are considered a paraphyletic grade, having evolved from trimerophytes and eventually giving rise to the earliest seed plants.
Reader's Guide
Progymnosperms hold a pivotal position in plant evolutionary history as the paraphyletic grade that bridges trimerophytes and seed plants. They are significant as the ancestors of the earliest seed plants (spermatophytes) and as the first true trees, with Archaeopteris representing the first really large trees. Their vascular cambium with unlimited growth potential and production of xylem and phloem allowed for substantial woody growth. The transition from homospory in Aneurophytales to heterospory in later groups marks a key step toward seed plant reproduction. The presence of pycnoxylic wood in both Archaeopteridales and Noeggerathiales indicates advanced wood anatomy. Their eventual decline and extinction by the end of the Permian closed a chapter that laid the foundation for the dominance of seed plants in terrestrial ecosystems.
Did You Know?
- Progymnosperms are a paraphyletic grade, not a monophyletic group.
- The earliest known progymnosperms are from the Middle Devonian order Aneurophytales.
- Archaeopteris, a Late Devonian progymnosperm, represents the first really large trees.
- The latest surviving progymnosperms, the Noeggerathiales, persisted until the end of the Permian.
More in Conifers And Gymnosperms 1-24
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