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What are progymnosperms?

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).

Did gymnosperms evolve from progymnosperms?

Palaeobotanists, such as Bonamo (1975) and Beck (1976) opined that gymnosperms have evolved from progymnosperms. The primitive aspects of Aneurophytales of Progymnosperms well- established. These members extend farthest back in the geological column and include three- dimensional branching system, terminal sporangia and a protostele.

Is Progymnospermopsida a landmark event in the history of vascular plant evolution?

Stewart (1981) considers the discovery of Progymnospermopsida as “a landmark event which has enhanced our understanding of vascular plant evolution and more than any other finding” after the discovery of Rhyme flora and ptendosperms. Essay # 2. Classification of Progymnosperms:

Do progymnosperms have a vascular cambium?

Progymnosperms evolved a vascular cambium that was bifacial, capable of producing not only xylem on its inner face (as in the more primitive lycophytes and sphenophytes) but also phloem on its outer face.

Which phylum evolved from progymnosperms?

Palaeobotanists, such as Bonamo (1975) and Beck (1976) opined that gymnosperms have evolved from progymnosperms. The primitive aspects of Aneurophytales of Progymnosperms well- established. These members extend farthest back in the geological column and include three- dimensional branching system, terminal sporangia and a protostele.

What are the three orders of Progymnospermopsida?

Some of the characters shared commonly by all the three orders (Pityales, Aneurophytales and Protopityales) of Progymnospermopsida include their:

What is the relationship between Archaeopteridales and Aneurophytales?

Close relation between Aneurophytales and Archaeopteridales is also evidenced by the discovery of ray tracheids and grouped pittings in the secondary wood of Archaeopteris of Archaeopteridales and Triloboxylon of Aneurophytales.

What fossils were found between fern-like fronds of Archaeopteris and gymnosper?

fern-like fronds of Archaeopteris and gymnosperm-like trunks of Callixylon, these members were grouped as a class of gymnosperms, the Progymnospermopsida by Beck (1960). According to Bonamo (1975) Progymnosperms are the “plants exhibiting the features of ptendophytic reproduction and gymnospermic anatomy”.

What is the link between gymnosperms and psilophytopsida?

Progymnosperms are thought to form a link between the Psilophytopsida (of pteridophytes ) and the gymnosperms. Some palaeobotanists consider Progymnosperms to represent the origin of both Cycadales and Coniferales. Progymnosperms are actually not true gymnosperms and are still classified by some botanists as pteridophytes.

Which phylum gave rise to Upper Devonain and Carboniferous members of Pteridospermales?

Some palaeobotanists also believe that Aneurophytales of Progymnosperms gave rise to Upper Devonain and Carboniferous members of Pteridospermales via Calamopitaceae of Palaeozoic Pteridosperms. Beck (1976) advocated that conifers originated from Archaeopteridales of progymnosperms.

Who divided the class Progymnospermopsida into three orders?

Beck (1960) divided the class Progymnospermopsida into following three orders, and the same classification has been followed by Spome (1974) and Sandra Holmes (1986):

Progymnosperms Definition

The progymnosperms belong to the kingdom of Plantae. They show monopodial growth with the greater production of secondary xylem. They appeared woody and produced spores. The plants evolved from the group of trimerophytes that gives the production of gymnosperms.

Overview of Progymnosperms

They come from the division of Progymnospermophyta, and were able to form Protopteridium. Protopteridium is a vegetative organ with groups of axes and are similar to gymnosperms that have vascular tissue for secondary growth. The secondary growth produces the wood and is able to grow like tall trees.

Ecology and Habitat

The first true trees are called Archaeopteris that are able to produce woods called cambium. The stems appeared robust, and the secondary growth occurs in the xylem that formed in the form of bifacial cambium. The stem shows monopodial growth.

Groups of Progymnosperms

In 1960, it is one of the most significant discoveries of paleobotanical identified by Charles B. Beck. They were able to identify fossil wood called Callixylon. Then, the leaves of progymnosperms are called Archaeopteris. They are similar parts of the plants that are trivial. The fossil record hardly ever conserves the whole organism’s intact.

Who created the definition of progymnosperms?

Bonamo (1975) created the strictest definition of progymnosperms: woody habit, pycnoxylic wood with narrow rays, complex branching systems, little differentiation among successive orders of branches, terminal sporangia, a free-sporing habit, and fertile leaves that are dichotomous and pinnate.

What is the definition of progymnospermopsida?

Bonamo (1975) created the strictest definition of progymnosperms: woody habit, pycnoxylic wood with narrow rays, complex branching systems, little differentiation among successive orders of branches, terminal sporangia, a free-sporing habit, and fertile leaves that are dichotomous and pinnate. ...

Which group of plants have a more complex morphology and anatomy?

The trimerophytes demonstrate more complex morphology and anatomy than rhyniophytes, their presumed ancestors, although both groups are coeval. In the trimerophytes, plant architecture is monopodial or pseudomonopodial. Laterals are produced in a variety of patterns, including helical ( Psilophyton sterile branches), alternately and distichous ( Psilophyton fertile branches), tristichous ( Trimerophyton ), and tetrastichous ( Pertica ). In Pertica the ultimate branchlets consist of slender, three-dimensional dichotomizing structures. It has been suggested that the planation of these lateral branches would provide the morphologic equivalent of a megaphyllous leaf and that Pertica may be used as a transitional morphotype in the evolution of a frond or a leaf. In another group of Devonian plants, the Aneurophytales (progymnosperms), some taxa possess planated laterals, whereas in others the branching systems are more three dimensional (Chapter 12 ).

Which fossil taxa have terminal polytomy?

Finally, the consensus tree for the 36 fossil taxa and Equisetum contains a terminal polytomy containing Archaeopteris – Lyginopteris, Eospermatopteris + Wattieza – Pseudosporochnus + Pietzchia, and Calamophyton–Equisetum–Calamites – Archaeocalamites ( Fig. 5.4 ). This polytomy is subtended by a series of branches composed of Elkinsia – Yiduxylon and Rhacophyton that is in turn subtended by taxa traditionally assigned to the progymnosperms ( Fig. 5.4 ).

Do lyginopteridales have affinities?

The cupulate fructifications of the Austrocalyxaceae suggest affinities in the Lyginopteridales. Arguing against lyginopteridalean affinities, however, is the fact that the taxa have rhacopteroid or triphyllopteroid unforked foliage, whereas lyginopteridalean foliage typically is forked (see above).

Is Psilophyton a trimerophyte?

princeps, there is a simple conducting strand, but one that is more massive than any known for the rhyniophytes. Conducting elements in the rhyniophytes are of the S-type, while Psilophyton contains P-type elements in which secondary wall material is deposited between the scalariform bars.

What are the Progymnosperms?

Introduction to the Progymnosperms. Progymnosperms were important components of the vegetation from the Middle Devonian through the Lower Mississipian. As their name implies, they were like the gymnosperms, but not quite.

What is the most primitive progymnosperm?

The aneurophytes are commonly considered the most primitive of the progymnosperms and appear to form an evolutionary intermediate between the plants of the "trimerophyte" grade and the heterosporous progymnosperms like Archaeopteris .

What are the two groups of progymnosperms?

Two major groups of progymnosperms are recognized, the Archaeopteridales and Aneurophytales . A third group, the Protopityales is sometimes recognized, but it is poorly known, and so its relationship to other plants is unclear.

Is a progymnosperm homosporous or heterosporous?

Some progymnosperms were homosporous, producing many identical spores, while others were heterosporous, producing two different kinds of spores. This latter group are thought to be ancestors, or at least close relatives, of the seed plants .

Do progymnosperms have pits?

The xylem of progymnosperms, however, had circular-bordered pits, which are similar, but not identical, to those of conifers. Therefore, some paleobotanists have reconsidered the proposed close relationship between conifers and the progymnosperms.