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
gymnosperms, 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 ...
(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
* ...
of division Progymnospermophyta or class Progymnospermopsida (as opposite). The stratigraphically oldest known examples belong to the Middle
Devonian 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
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 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 251.9 Mya. It is the last ...
.
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 xy ...
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 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 c ...
.
*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 is ...
but others were
homosporous.
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
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