SEM Studies on Vessels in Ferns. 20. Hawaiian Hymenophyllaceae

Abstract

Tracheary elements of three species (Mecodium recurvum, Vandenboschia devallioides, and Callistopteris baldwinii) (two epiphytic, one terrestrial) representing three genera of Hymenophyllaceae were studied with scanning electron microscopy (SEM). Both roots and rhizomes of all three species possess vessel elements. Wide perforations, an expression of pit (perforation) dimorphism within perforation plates, are prominent, more so than in most other fern families. Monomorphic perforations are also common, as are perforations in which weblike or porose pit membranes are present. Habitats of Hymenophyllaceae are characterized by high humidity with little fluctuation. However, fluctuation in moisture availability within the substrates of Hymenophyllaceae may be related to the abundance of vessels and the distinctiveness of the perforation plates. A peculiarity of hymenophyllaceous tracheary elements not hitherto reported in ferns to our knowledge is reported: gaps in the secondary wall pattern at outer surface of cell angles. These gaps take the form of rhomboidal depressions or a continuous depressed strip.