Pteridospermatophyta
Encyclopedia
The term Pteridospermatophyta (or "seed ferns") refers to several distinct groups of extinct seed-bearing plants (spermatophytes). The oldest fossil evidence of plants of this type is of late Devonian
age, and they flourished particularly during the Carboniferous
and Permian
periods. Pteridosperms declined during the Mesozoic
Era and had mostly disappeared by the end of the Cretaceous
Period, though some fossil
pteridosperm-like plants seem to have survived into Eocene
times in Tasmania
.
The concept of the pteridosperms goes back to the late 19th century when palaeobotanists came to realise that many Carboniferous
fossils resembling fern fronds had anatomical features more reminiscent of the modern-day seed plants the cycads. In 1899 the German palaeobotanist Henry Potonié coined the term "Cycadofilices" ("cycad-ferns") for such fossils, suggesting that they were a group of non-seed plants intermediate between the fern
s and cycad
s. Shortly afterwards, the British palaeobotanists Frank Oliver
and Dukinfield Henry Scott
(with the assistance of Oliver's student at the time Marie Stopes
) made the critical discovery that some of these fronds (genus Lyginopteris) were associated with seeds (genus Lagenostoma) that had identical and very distinctive glandular hairs, and concluded that both fronds and seeds belonged to the same plant. Soon, additional evidence came to light suggesting that seeds were also attached to the Carboniferous fern-like fronds Dicksonites, Neuropteris and Aneimites. Initially it was still thought that they were intermediate between the ferns and cycads, and especially in the English-speaking world they were referred to as "seed ferns" or "pteridosperms". Today, though most palaeobotanists regard them as being only distantly related to ferns and these names as misleading, but the names have nevertheless stuck. Nowadays, four orders of Palaeozoic seed plants tend to be referred to as pteridosperms: Lyginopteridales
, Medullosales
, Callistophytales
and Peltaspermales.
Their discovery attracted considerable attention at the time, as the pteridosperms were the first extinct group of vascular plants to be identified solely from the fossil record. In the 19th century the Carboniferous Period was often referred to as the "Age of Ferns" but these discoveries during the first decade of the 20th century made it clear that the "Age of Pteridosperms" was perhaps a better description.
During the 20th century the concept of pteridosperms was expanded to include various Mesozoic groups of seed plants with fern-like fronds, such as the Corystospermales and Leptostrobales. Some palaeobotanists also included seed plant groups with entire leaves such as the glossopterids
(Arberiales) and Gigantopteridales, which was clearly stretching the concept. In the context of modern phylogenetic models, the groups often referred to as pteridosperms appear to be liberally spread across a range of clades, and many palaeobotanists today would regard pteridosperms as little more than a paraphyletic 'grade-group' with no common lineage. One of the few characters that may unify the group is that the ovules were borne in a cupule, but this has not been confirmed for all "pteridosperm" groups.
So, does the concept of pteridosperms have any value today? Many palaeobotanists still use the term in an informal sense for the seed plants that are not angiosperms, coniferoids (conifers or cordaites), ginkgophytes or cycadophytes (cycads or bennettite
s). This is particularly useful for extinct seed plant groups, whose systematic relationships remain speculative; we can call them pteridosperms with no implications being made as to their systematic affinities. Also, from a purely curatorial or collecting perspective the term pteridosperms is a useful shorthand for describing the fern-like fronds that were probably produced by seed plants, which are commonly found in many Palaeozoic and Mesozoic fossil floras
The following Order
s of seed plants are often referred to as pteridosperms:
Devonian
The Devonian is a geologic period and system of the Paleozoic Era spanning from the end of the Silurian Period, about 416.0 ± 2.8 Mya , to the beginning of the Carboniferous Period, about 359.2 ± 2.5 Mya...
age, and they flourished particularly during the Carboniferous
Carboniferous
The Carboniferous is a geologic period and system that extends from the end of the Devonian Period, about 359.2 ± 2.5 Mya , to the beginning of the Permian Period, about 299.0 ± 0.8 Mya . The name is derived from the Latin word for coal, carbo. Carboniferous means "coal-bearing"...
and Permian
Permian
The PermianThe term "Permian" was introduced into geology in 1841 by Sir Sir R. I. Murchison, president of the Geological Society of London, who identified typical strata in extensive Russian explorations undertaken with Edouard de Verneuil; Murchison asserted in 1841 that he named his "Permian...
periods. Pteridosperms declined during the Mesozoic
Mesozoic
The Mesozoic era is an interval of geological time from about 250 million years ago to about 65 million years ago. It is often referred to as the age of reptiles because reptiles, namely dinosaurs, were the dominant terrestrial and marine vertebrates of the time...
Era and had mostly disappeared by the end of the Cretaceous
Cretaceous
The Cretaceous , derived from the Latin "creta" , usually abbreviated K for its German translation Kreide , is a geologic period and system from circa to million years ago. In the geologic timescale, the Cretaceous follows the Jurassic period and is followed by the Paleogene period of the...
Period, though some fossil
Fossil
Fossils are the preserved remains or traces of animals , plants, and other organisms from the remote past...
pteridosperm-like plants seem to have survived into Eocene
Eocene
The Eocene Epoch, lasting from about 56 to 34 million years ago , is a major division of the geologic timescale and the second epoch of the Paleogene Period in the Cenozoic Era. The Eocene spans the time from the end of the Palaeocene Epoch to the beginning of the Oligocene Epoch. The start of the...
times in Tasmania
Tasmania
Tasmania is an Australian island and state. It is south of the continent, separated by Bass Strait. The state includes the island of Tasmania—the 26th largest island in the world—and the surrounding islands. The state has a population of 507,626 , of whom almost half reside in the greater Hobart...
.
The concept of the pteridosperms goes back to the late 19th century when palaeobotanists came to realise that many Carboniferous
Carboniferous
The Carboniferous is a geologic period and system that extends from the end of the Devonian Period, about 359.2 ± 2.5 Mya , to the beginning of the Permian Period, about 299.0 ± 0.8 Mya . The name is derived from the Latin word for coal, carbo. Carboniferous means "coal-bearing"...
fossils resembling fern fronds had anatomical features more reminiscent of the modern-day seed plants the cycads. In 1899 the German palaeobotanist Henry Potonié coined the term "Cycadofilices" ("cycad-ferns") for such fossils, suggesting that they were a group of non-seed plants intermediate between the fern
Fern
A fern is any one of a group of about 12,000 species of plants belonging to the botanical group known as Pteridophyta. Unlike mosses, they have xylem and phloem . They have stems, leaves, and roots like other vascular plants...
s and cycad
Cycad
Cycads are seed plants typically characterized by a stout and woody trunk with a crown of large, hard and stiff, evergreen leaves. They usually have pinnate leaves. The individual plants are either all male or all female . Cycads vary in size from having a trunk that is only a few centimeters...
s. Shortly afterwards, the British palaeobotanists Frank Oliver
Francis Wall Oliver
Francis Wall Oliver FRS was a British botanist. He was Quain Professor of Botany at University College London 1890-1925 and then Professor of Botany at the University of Cairo 1929–1935. He was elected a Fellow of the Royal Society in 1905. He was awarded the Linnean Medal in 1925.- References :...
and Dukinfield Henry Scott
Dukinfield Henry Scott
Dukinfield Henry Scott FRS was a British botanist.The architect Sir George Gilbert Scott was his father...
(with the assistance of Oliver's student at the time Marie Stopes
Marie Stopes
Marie Carmichael Stopes was a British author, palaeobotanist, campaigner for women's rights and pioneer in the field of birth control...
) made the critical discovery that some of these fronds (genus Lyginopteris) were associated with seeds (genus Lagenostoma) that had identical and very distinctive glandular hairs, and concluded that both fronds and seeds belonged to the same plant. Soon, additional evidence came to light suggesting that seeds were also attached to the Carboniferous fern-like fronds Dicksonites, Neuropteris and Aneimites. Initially it was still thought that they were intermediate between the ferns and cycads, and especially in the English-speaking world they were referred to as "seed ferns" or "pteridosperms". Today, though most palaeobotanists regard them as being only distantly related to ferns and these names as misleading, but the names have nevertheless stuck. Nowadays, four orders of Palaeozoic seed plants tend to be referred to as pteridosperms: Lyginopteridales
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; they are the stratigraphically oldest-known pteridosperms, occurring first in late Devonian...
, Medullosales
Medullosales
The Medullosales is an order of pteridospermous seed plants characterised by large radiospermic ovules with a vascularised nucellus, complex pollen-organs, stems and rachises with a dissected stele, and frond-like leaves. Their nearest still-living relatives are probably the cycads.Most...
, Callistophytales
Callistophytales
The Callistophytales was an order of mainly scrambling and lianescent plants found in the wetland "coal swamps" of Euramerica and Cathaysia. They were characterised by having bilaterally-symmetrical, non-cupulate ovules attached to the underside of pinnules that were morphologically similar to the...
and Peltaspermales.
Their discovery attracted considerable attention at the time, as the pteridosperms were the first extinct group of vascular plants to be identified solely from the fossil record. In the 19th century the Carboniferous Period was often referred to as the "Age of Ferns" but these discoveries during the first decade of the 20th century made it clear that the "Age of Pteridosperms" was perhaps a better description.
During the 20th century the concept of pteridosperms was expanded to include various Mesozoic groups of seed plants with fern-like fronds, such as the Corystospermales and Leptostrobales. Some palaeobotanists also included seed plant groups with entire leaves such as the glossopterids
Glossopteridales
Glossopteridales is an extinct order of plants belonging to Pteridospermatophyta, or Seed Ferns. They arose at the beginning of the Permian on the southern continent of Gondwana, but dwindled to extinction by the end of the Permian period . The best known genus is Glossopteris.- External links :*...
(Arberiales) and Gigantopteridales, which was clearly stretching the concept. In the context of modern phylogenetic models, the groups often referred to as pteridosperms appear to be liberally spread across a range of clades, and many palaeobotanists today would regard pteridosperms as little more than a paraphyletic 'grade-group' with no common lineage. One of the few characters that may unify the group is that the ovules were borne in a cupule, but this has not been confirmed for all "pteridosperm" groups.
So, does the concept of pteridosperms have any value today? Many palaeobotanists still use the term in an informal sense for the seed plants that are not angiosperms, coniferoids (conifers or cordaites), ginkgophytes or cycadophytes (cycads or bennettite
Bennettitales
Bennettitales is an extinct order of seed plants that first appeared in the Triassic period and became extinct toward the end of the Cretaceous...
s). This is particularly useful for extinct seed plant groups, whose systematic relationships remain speculative; we can call them pteridosperms with no implications being made as to their systematic affinities. Also, from a purely curatorial or collecting perspective the term pteridosperms is a useful shorthand for describing the fern-like fronds that were probably produced by seed plants, which are commonly found in many Palaeozoic and Mesozoic fossil floras
The following Order
Order (biology)
In scientific classification used in biology, the order is# a taxonomic rank used in the classification of organisms. Other well-known ranks are life, domain, kingdom, phylum, class, family, genus, and species, with order fitting in between class and family...
s of seed plants are often referred to as pteridosperms:
- Arberiales (= "GlossopteridalesGlossopteridalesGlossopteridales is an extinct order of plants belonging to Pteridospermatophyta, or Seed Ferns. They arose at the beginning of the Permian on the southern continent of Gondwana, but dwindled to extinction by the end of the Permian period . The best known genus is Glossopteris.- External links :*...
") - Calamopityales
- CallistophytalesCallistophytalesThe Callistophytales was an order of mainly scrambling and lianescent plants found in the wetland "coal swamps" of Euramerica and Cathaysia. They were characterised by having bilaterally-symmetrical, non-cupulate ovules attached to the underside of pinnules that were morphologically similar to the...
- Corystospermales
- Gigantopteridales
- Leptostrobales
- LyginopteridalesLyginopteridalesThe 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; they are the stratigraphically oldest-known pteridosperms, occurring first in late Devonian...
- MedullosalesMedullosalesThe Medullosales is an order of pteridospermous seed plants characterised by large radiospermic ovules with a vascularised nucellus, complex pollen-organs, stems and rachises with a dissected stele, and frond-like leaves. Their nearest still-living relatives are probably the cycads.Most...
- Peltaspermales