Vestured pits: a diagnostic character in the secondary xylem of Myrtales

Vestures are small projections from the secondary cell wall associated with tracheary elements of the secondary xylem. They are usually associated with bordered pits and characterize various angiosperm families, including important timber species such as Dipterocarpaceae and Eucalyptus trees. The micromorphology and distribution of vestures were studied in 22 species representing all families within the order Myrtales based on light and scanning electron microscopy. Vestures are consistently present near the outer pit aperture of bordered vessel pits, suggesting the synapomorphic character of this feature for the entire order. It is unclear in which geological period this feature originated in the evolution of the pre-Myrtalean lineages. In some species vestures are associated with inner pit apertures, inner vessel walls, simple perforation plates, depressions of the cell wall and bordered pits of tracheids or fibre-tracheids. A compact network of branched vestures almost completely filling the entire pit chamber is the most common vestured pit type in Myrtales, although considerable variation may occur within a wood sample. The micromorphology of vestures seems to some extent correlated with quantitative pit characters. Understanding the exact function of vestured pits with respect to hydraulic efficiency and safety remains a challenge.