Wood and bark of Buddleja: uniseriate phellem, and systematic and ecological patterns

Abstract

Wood anatomy of Buddleja is well-explored but not in many southern African members, which form a grade of species and small clades that form successive sister groups to the rest of the genus, and its bark structure has not been studied at all. We provide new descriptions of wood anatomy for twelve species, including nearly all Buddleja from southern Africa and two species of Freylinia in the sister group of Buddleja. We also describe bark structure from fifteen species. To assess if wood anatomy provides phylogenetic and/or ecological signal, we compiled data on wood traits and climatic variables from the distributions of 53 species. Wood traits counteracting cavitation correlated with higher temperature and precipitation seasonality; simultaneously they were better expressed in species with smaller maximal plant height. It is likely that hotter and drier areas harbour smaller plants which have traits conveying higher conductance safety. Bark structure varies considerably. In bark of Buddleja section Gomphostigma, periderm is initiated in the outer cortex and develops thin-walled phellem, and sclerification of their phloem does not occur. This resembles bark in Freylinia, supporting the position of section Gomphostigma as sister to the rest of Buddleja. In the remaining Buddleja species, bark is characterised by formation of periderm with phelloid cells in the secondary phloem. The phellem is often uniseriate, a condition not reported elsewhere. Its formation occurs close in time to solid sclerification of the cut-off phloem, suggesting a possible novel ontogenetic mechanism.

Wood and bark structure inBuddleja: anatomical background of stem morphology

“… Infrageneric relationships in Buddleja and a summary of its bark anatomy. Phylogenetic tree inferred by Chau et al (2017) that was supported by subsequent bark anatomical analyses by Frankiewicz et al (2020) , with sect. Gomphostigma marked in blue dashed line (representing uncertain position), and African taxa in bold.…”

“…Only formally recognized clades are named, and clade triangle size approximates species richness, while monospecific clades are solitary lines. The most important anatomical differences between the two types of barks found in Buddleja and closely related Freylinia reported by Frankiewicz et al (2020) are given at far right. The upper photo is from B. glomerata (sect.…”

Derived woodiness and annual habit evolved in African umbellifers as alternative solutions for coping with drought

“…Since quantitative wood traits are likely influenced primarily by plant height, we focus here on qualitative characteristics [ 61 , 62 ]. Although restricted number of available specimens prohibits far-fetched comparisons, our results show that the Lefebvrea clade representatives have wood similar to other southern African lineages, despite of being only distantly related.…”

Wood and bark anatomy of South African Picrodendraceae with systematic and ecological implications

“…The conti nuous bands of sclereids and fibers can also perform an additional protection for the conducting secondary phloem that can be suffered otherwise by fissuring of bark due to its dila ta tion. The protective role of sclerified secon da ry phloem has been shown, for instance, in the bark of Buddleja, a genus of Scrophulariaceae (Frankiewicz et al 2021).…”