The progymnosperms are an extinct group of woody, spore-bearing plants that is presumed to have evolved from the trimerophytes, and eventually gave rise to the spermatophytes, ancestral to both

gymnosperms The gymnosperms ( ; ) are a group of woody, perennial Seed plant, seed-producing plants, typically lacking the protective outer covering which surrounds the seeds in flowering plants, that include Pinophyta, conifers, cycads, Ginkgo, and gnetoph ...

and angiosperms (flowering plants). They have been treated formally at the rank of division Progymnospermophyta or class Progymnospermopsida (as opposite). The stratigraphically oldest known examples belong to the Middle

Devonian The Devonian ( ) is a period (geology), geologic period and system (stratigraphy), system of the Paleozoic era (geology), era during the Phanerozoic eon (geology), eon, spanning 60.3 million years from the end of the preceding Silurian per ...

order the Aneurophytales, with forms such as '' Protopteridium'', in which the vegetative organs consisted of relatively loose clusters of axes. '' Tetraxylopteris'' is another example of a genus lacking leaves. In more advanced aneurophytaleans such as '' Aneurophyton'' these vegetative organs started to look rather more like fronds, and eventually during Late Devonian times the aneurophytaleans are presumed to have given rise to the pteridosperm order, the Lyginopteridales. In Late Devonian times, another group of progymnosperms gave rise to the first really large trees known as '' Archaeopteris''. The latest surviving group of progymnosperms is the Noeggerathiales, which persisted until the end of the

Permian The Permian ( ) is a geologic period and System (stratigraphy), stratigraphic system which spans 47 million years, from the end of the Carboniferous Period million years ago (Mya), to the beginning of the Triassic Period 251.902 Mya. It is the s ...

. Other characteristics: *

Vascular cambium The vascular cambium is the main growth tissue in the stems and roots of many plants exhibiting secondary growth, specifically in dicots such as buttercups and oak trees, gymnosperms such as pine trees, as well as in certain other vascular ...

with unlimited growth potential is present as well as

xylem Xylem is one of the two types of transport tissue (biology), tissue in vascular plants, the other being phloem; both of these are part of the vascular bundle. The basic function of the xylem is to transport water upward from the roots to parts o ...

and

phloem Phloem (, ) is the living tissue in vascular plants that transports the soluble organic compounds made during photosynthesis and known as ''photosynthates'', in particular the sugar sucrose, to the rest of the plant. This transport process is ...

. *Ancestors of the earliest seed plants as well as the first true trees. *Strong

monopodial Vascular plants with monopodial growth habits grow upward from a single point. They add leaves to the apex each year and the stem grows longer accordingly. The word ''Monopodial'' is derived from Greek language, Greek '', ''one'' and '', "foot", in ...

growth is exhibited. *Aneurophytales was homosporous, while the remaining groups were heterosporous.

Phylogeny

Progymnosperms are a paraphyletic grade of plants.

References

External links

Progymnospermophyta

Botany: an introduction to plant biology
Middle Devonian first appearances Middle Devonian plants Mississippian plants Mississippian extinctions Late Devonian plants Paraphyletic groups Prehistoric plant taxa {{permian-plant-stub