Progymnospermes

The progymnospermes consituent a group of known fossil plants to the Dévonien and the Carbonifère. They are currently regarded as the group-brother of the plants with seeds (Gymnospermes, Angiospermes). The Clade which includes/understands the progymnospermes + all the plants with seeds is sometimes called “Lignophytes”. The Synapomorphie of Lignophytes would be the possession of a vascular Cambium bifacial.

The progymnospermes had an anatomy which points out the Gymnospermes but reproduced with Spores like the ferns and not with Graine S. Among the progymnospermes one distinguishes:

  • the aneurophytales , of the small plants of average Dévonien and superior which were homosporées (only one type of spores).
  • the archaeopteridales which could reach big sizes and which were hétérosporées (Mégaspore S and Microspore S). Archaeopteris is rebuilt as a tree which could reach 30 to 40 m in height.
  • the protopityales , a badly known group of the beginning of Carboniferous represented by trunks and small hétérosporés fertile axes.

Certain authors also arrange in the progymnospermes the néoggerathiales , a known problematic group of the Carbonifère higher than the Trias.

Described kinds

In an article of synthesis of 1988, C. Beck and D. Wight recognize tax them following, known by permineralized compressions and/or axes.

Aneurophytales

  • Aneurophyton (Dévonien means-superior, the USA and Europe)
  • Triloboxylon (Dévonien means-superior, the USA)
  • Tetraxylopteris (Dévonien means-superior, the USA and Venezuela)
  • Rellimia (Dévonien means-superior, Europe and the ex-USSR)
  • Proteokalon (average Dévonien, the USA)
  • Cairoa (average Dévonien, the USA)
  • Reimannia (average Dévonien, the USA)

Archaeopteridales

  • Archaeopteris (means-Carboniferous Dévonien)
  • Eddya (average Dévonien, the USA)
  • Siderella (Carboniferous inferior, the USA)
  • Svalbardia (average Dévonien)
  • Actinoxylon (average Dévonien)
  • Actinopodium (average Dévonien)

  • ? Cecropsis (Carboniferous)

Protopityales
  • Protopitys (Carboniferous inferior, Europe)

Progymnospermes and the origin of the plants with seeds

Since the creation of the group of the progymnospermes by Charles Beck in 1960, the progymnospermes were regarded as groups it from which the Plantes with seeds evolved/moved. As the plants with seeds have only one functional Mégaspore by mégasporange, the majority of the paleobotanists consider that the hétérosporie (distinction between microspores small and many and mégaspores large and very few) consitue an intermediate stage. The ancestor of the plants with seeds would be thus a progymnosperme hétérosporée like Archaeopteris . However, certain paleobotanists consider that a hétérosporé intermediary is not obligatory. In this case the plants with seeds could have evolved/moved directly starting from progymnospermes homosporées like the aneurophytales.

External bonds

Progymnosperms

Origin of seed (in English)

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