Wood Anatomy of Lamiaceae. A Survey, with Comments on Vascular and Vasicentric Tracheids

Quantitative and qualitative data are presented for 44 collections representing 42 species in 27 genera. Lamiaceae basically have: vessels with simple perforation plates; vessel-to-vessel pitting alternate; imperforate tracheary elements alllibriform fibers, fibers commonly septate; axial parenchyma scanty vasicentric; rays Heterogeneous Type liB. These features ally Lamiaceae closely with Verbenaceae. In addition to the Mesomorphy ratio (based on vessel element dimensions), features that indicate wood xeromorphy in Lamiaceae, in probable increasing order of importance are: presence of indistinct to marked growth rings; presence of helical thickenings in vessels; presence of vasicentric or vascular tracheids; presence of vessel groups averaging three or more vessels per group. More mesomorphic woods in Lamiaceae occur in species that are arborescent to shrubby, and that occur in areas that have no prolonged drought. Helical sculpture in vessels is expressed not only as thickenings, but also as grooves interconnecting pit apertures (coalesced pit apertures), and inconspicuous thickenings in pairs along the grooves. Vascular tracheids (at ends of growth rings) occur in several genera. Where growth rings are very narrow (Salvia, Trichostema), vessels and tracheids are intermixed, thereby justifYing description as vasicentric tracheids of what may have originated phylogenetically as vascular tracheids. This may represent one pathway for origin of vasicentric tracheids. Wide bands of axial parenchyma in Cuminia and Leptosceptrum have originated as a result of fiber dimorphism. Abundance of upright cells in numerous Lamiaceae is indicative ofpaedomorphosis, and may point to secondary woodiness in some instances; the family as a whole appears ancestrally moderately woody. The ratio between libriform fiber length and vessel element length marks Lamiaceae as specialized. Crystal presence and cambial variants are newly reported for the family.