The progymnosperms are an extinct group of woody, spore-bearing plants that is presumed to have evolved from the

trimerophyte Trimerophytopsida (or Trimeropsida) is a class of early vascular plants from the Devonian, informally called trimerophytes. It contains genera such as ''Psilophyton''. This group is probably paraphyletic, and is believed to be the ancestral group ...

s, and eventually gave rise to the

gymnosperms The gymnosperms ( lit. revealed seeds) are a group of seed-producing plants that includes conifers, cycads, ''Ginkgo'', and gnetophytes, forming the clade Gymnospermae. The term ''gymnosperm'' comes from the composite word in el, γυμνό� ...

, ancestral to acrogymnosperms and

angiosperms Flowering plants are plants that bear flowers and fruits, and form the clade Angiospermae (), commonly called angiosperms. The term "angiosperm" is derived from the Greek words ('container, vessel') and ('seed'), and refers to those plants th ...

(flowering plants). They have been treated formally at the

rank Rank is the relative position, value, worth, complexity, power, importance, authority, level, etc. of a person or object within a ranking, such as: Level or position in a hierarchical organization * Academic rank * Diplomatic rank * Hierarchy * H ...

of division Progymnospermophyta or class Progymnospermopsida (as opposite). The stratigraphically oldest known examples belong to the Middle

Devonian The Devonian ( ) is a geologic period and system of the Paleozoic era, spanning 60.3 million years from the end of the Silurian, million years ago (Mya), to the beginning of the Carboniferous, Mya. It is named after Devon, England, whe ...

order the Aneurophytales, with forms such as '' Protopteridium'', in which the vegetative organs consisted of relatively loose clusters of axes. ''

Tetraxylopteris '' Tetraxylopteris'' is a genus of extinct vascular plants of the Middle to Upper Devonian (around ). Fossils were first found in New York State, USA. A second species was later found in Venezuela. Description Fossils of ''Tetraxylopteris'' ha ...

'' is another example of a genus lacking leaves. In more advanced aneurophytaleans such as ''

Aneurophyton ''Aneurophyton'' is a genus of extinct vascular plants that belong to the Aneurophytales, a class of progymnosperms. The genus is primarily known from records of two well-known species found in mostly Middle Devonian and Upper Devonian (late Eif ...

'' 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 The term Pteridospermatophyta (or "seed ferns" or "Pteridospermatopsida") is a polyphyletic group of extinct seed-bearing plants (spermatophytes). The earliest fossil evidence for plants of this type is the genus ''Elkinsia'' of the late Devonian ...

order, the

Lyginopteridales The Lyginopteridales were the archetypal pteridosperms: They were the first plant fossils to be described as pteridosperms and, thus, the group on which the concept of pteridosperms was first developed;Oliver, F. W. & Scott, D. H. (1904). "On t ...

. In Late Devonian times, another group of progymnosperms gave rise to the first really large trees known as ''

Archaeopteris ''Archaeopteris'' is an extinct genus of progymnosperm tree with fern-like leaves. A useful index fossil, this tree is found in strata dating from the Upper Devonian to Lower Carboniferous (), the oldest fossils being 385 million years old, ...

''. The latest surviving group of progymnosperms is the

Noeggerathiales Noeggerathiales is a now-extinct order of vascular plants. The fossil range of the order extends from the Upper Carboniferous to the upper Permian (Lopingian). Due to gaps in the fossil record, the group is incompletely known and poorly defined, ...

, which persisted until the end of the

Permian The Permian ( ) is a geologic period and 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 251.9 Mya. It is the last period of the Paleoz ...

. Other characteristics: *

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

with unlimited growth potential is present as well as

xylem Xylem is one of the two types of transport tissue in vascular plants, the other being phloem. The basic function of xylem is to transport water from roots to stems and leaves, but it also transports nutrients. The word ''xylem'' is derived from ...

and

phloem Phloem (, ) is the living biological tissue, 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 tran ...

. *Ancestors of the earliest

seed plant A spermatophyte (; ), also known as phanerogam (taxon Phanerogamae) or phaenogam (taxon Phaenogamae), is any plant that produces seeds, hence the alternative name seed plant. Spermatophytes are a subset of the embryophytes or land plants. They inc ...

s 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 "mono-", ''one'' and "podial", "foot", in refe ...

growth is exhibited. *Some were

heterosporous Heterospory is the production of spores of two different sizes and sexes by the sporophytes of land plants. The smaller of these, the microspore, is male and the larger megaspore is female. Heterospory evolved during the Devonian period from isos ...

but others were

homosporous In biology, a spore is a unit of sexual or asexual reproduction that may be adapted for dispersal and for survival, often for extended periods of time, in unfavourable conditions. Spores form part of the life cycles of many plants, algae, ...

Phylogeny

Progymnosperms are a paraphyletic grade of plants.

References

External links

ProgymnospermophytaBotany: 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