TRACHEARY ELEMENTS IN PTERIDOPHYTES | BIONATURE

The origin of tracheary components is linked to plant migration from an aquatic to a terrestrial state. The conducting elements of early vascular land plants that persisted during the Silurian and Devonian periods were endowed with rudimentary types of lignification, such as annular and spiral thickenings. Different classes of Early Pteridophytes, such as Trimerophytopsida, Lycopsida, and Sphenopsida, developed scalariform and pitted tracheids independently. The structure of tracheids in various pteridophytic plants is described, starting with the earliest known extinct pteridophyte Cooksonia and progressing to the highly advanced heterosporous species Azolla. Some taxonomically distinct genera, including as Selaginella, Equisetum, Pteridium, Adiantum, Actiniopteris, Marsilea, and Regnellidium, have vessel elements. Multiporate terminal holes are present in all of the vessel elements. It is thought that the vessels of pteridophytes are polyphyletic in origin and are related to the function, i.e. xeric habit, rather than phylogeny. On the basis of the structure of tracheary elements, the relationship between distinct Pteridophyte groups is examined.

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