Wood and bark structure inBuddleja: anatomical background of stem morphology

Abstract

Background Bark (all tissues outside of the vascular cambium) has been extensively studied in recent years, especially its anatomy and physiology. Macromorphological bark characters can be important taxonomically for many plant groups, including the genus Buddleja (Scrophulariaceae). However, the relationship between macroscopic bark appearance and its microscopic structure remains obscure, hampering the use and interpretation of bark traits in plant taxonomy and phylogenetics as well as in other fields of botany. We studied micro- and macrostructure of bark in the species of Buddleja representing wide taxonomic and geographic diversity to identify general relationships between bark anatomy and morphology. We also examined Buddleja xylem and discussed the importance of anatomical traits for understanding the relationships between clades in this genus. Results The smooth bark surface in sect. Gomphostigma and the outgroup (Freylinia spp.) relates to the small number of periderms of superficial origin and limited sclerification. This allows for the retention of visible lenticels. In the rest of Buddleja, bark sloughs off and division of labour is present: collapsed phloem undergoes sclerification and acts as a protective layer, while thin-walled phellem forms the separation layers. A similar pattern is found in some groups (e.g., Lonicera), but in others (e.g., Vitis and the species of Eucalyptus with stringy bark), the pattern is inversed. Wood and bark anatomy supports a sister relationship between the southern African section Gomphostigma and the rest of Buddleja but is taxonomically uninformative among remaining clades. Conclusions Limited development of periderms and sclerification allow for the retention of a smooth bark surface and conspicuous lenticels. Sloughing off of bark requires division of labour into a lignified protective layer and a thin-walled separation layer. These two functions are never served by a single tissue but are rather divided between phloem and periderm. How more subtle features (e.g., size and shape of fissures) are determined requires further study. Simultaneously, bark anatomy could be a useful source of data to complement molecular phylogenetic studies in a total evidence approach for systematics.

Bark anatomy of Polylepis (Rosaceae): a loose stratified phellem instead of the lenticels?

“…The lack of phelloderm would imply a shift of cork cambium acti vity from bifacial to unifacial mode, but such cases are unknown. Recently, Frankiewicz et al (2021) did not re cognize phelloderm in the periderm of peeling bark in some spe cies of Buddleja L. (Scrophulariaceae), but this layer has been found in its periderm after careful examination (Frankiewicz et al 2023).…”

“…This pattern is the most common among the taxa with peeling barks: it has been found, for ins tance, in species of Eucalyptus L'Hér. with stringy barks (Chattaway 1955), in Melaleuca L. (Chiang & Wang 1984, Crivellaro & Schweingruber 2013, Lonicera L. (Eremin & Kopanina 2012, Schweingruber et al, 2019 and Buddleja (Frankiewicz et al 2021(Frankiewicz et al , 2023. Unlike C. strobilifera, C. ruscifolia (Fig.…”

“…It is important to stress, however, that the definition of periderm as "secondary protec tive tissue" recommended by Angyalossy et al (2016: p. 576) is not necessarily relevant for the plants with peeling bark (sensu Shtein et al 2023), including Polylepis and related genera. In the barks of such architectural type, the periderm commonly serves only as a separation layer while the protective function is confined to sclerified secondary phloem (Frankiewicz et al 2021(Frankiewicz et al , 2023.…”

Properties of Bark Particleboard Bonded with Demethylated Lignin Adhesives Derived from <i>Leucaena leucocephala</i> Bark

“…Bark frequently has higher concentrations of extractives than wood grain, such as tannins and resins [26]. Furthermore, differences in the arrangement of phenolic chemicals and links within the chemical structure of lignin in bark may have an impact on the reactivity and characteristics of this material [27]. Bark powder and wood flour can also have different physical properties.…”