Vessel elements of two thelypteroid ferns-part I.

Background: Hydraulically efficient xylem was evolved in the vascular plants as an apomorphy of the group. Main xylem components involved in water conduction are tracheid and vessel. Vessels, in which two ends are perforated, constituted major evolutionary innovation within vascular plants, presumably providing more efficient solute conduction. Not all vascular plants have vessels. In pteridophytes vessels are present only in seven genera. The contention lies regarding the presence and distribution of vessel in pteridophytes are the impulsive force of this investigation.

Methods: Tracheary elements are isolated following the standard maceration technique, then hand-razor cut longisections are passed through the aqueous alcohol grades and air-dried samples are placed on stub, sputter coated with gold and examined with SEM.

Results: Two thelypteroid ferns viz. Ampelopteris prolifera (Retz.) Copel. and Thelypteris interrupta (Willd.) K. Iwats. are having vessel elements in root, rhizome, stipe, rachis, primary vein/costa, root-rhizome and rhizome-petiole junction i.e. through entire vascular connection of the plant body though the vessel network is interrupted and joined with parenchyma at the end in some places. Presence of vessel elements in the costa of pteridophytic taxa is first time reported by this study. Vessel end-walls are obliquely placed (root, rhizome, and stipe) but oblique to horizontal orientation is noticed in the primary vein/costa. End-walls are with simple, intermediate and compound perforation plates observed through SEM imaging as well as with tissue specific stain. Studied taxa are grown either in terrestrial microclimate of two contrasting environments i.e. sun and shade (A. prolifera) or in open swampy land (T. interrupta) with moderate to highly disturbed places as rapid proliferating populations showing interpopulation variations of tracheary elements length-width(s) and vessel end-wall length-width(s).

Conclusion: Vessel elements are present throughout the entire vascular connections of the plant body of A. prolifera (Retz.) Copel. and T. interrupta (Willd.) K. Iwats. Interpopulation variation of tracheary elements length-width(s) and vessel end-wall length width(s) are noticed. Till date only seven genera of pteridophytes are reported for the presence of vessel and these two genera are the new addition with the previous.