Picoli, EdgardJacomini, FrancielyLadeira, JosimarAlmeida, Maria NarunaVidaurre, GrazielaMoulin, JordãoZauza, EdivalGuimarães, LúcioIsaias, Rosy MaryBalmant, Kellyda Costa, Weverton2026-01-152026-01-152025-07-08International Journal of Horticultural Science, Vol. 31 (2025) , 73-87.1585-0404https://hdl.handle.net/2437/402489Abiotic stresses trigger the Eucalyptus Physiological Disorder (EPD) which poses a threat to planted and native stands. This research seeks links between eucalyptus bark histological features and EPD, in which the descriptive bark anatomy and histochemistry are approached. Barks from 5-year eucalyptus trees, from commercial clones of E. grandis , E. urophylla and its hybrids, were collected at breast height (DBH), and 50% and 75% of the commercial height, and evaluated. The eucalyptus bark consisted of a periderm (or rhytidome) and a secondary phloem with conspicuous solitary sieve tube elements (STE). The outer bark revealed a secondary phloem with collapsed STE, whereas its inner counterpart displayed non-collapsed STEs. A region crowded with calcium oxalate (CaOx) crystals in axial parenchyma, covering the non-collapsed and partially overlapped collapsed secondary phloem, was observed. Eucalyptus barks exhibited similar anatomical organization at DBH, 50% and 75% of the commercial height, irrespective of expected EPD phenotype or scores. Notwithstanding, there are qualitative differences that are associated with the proportion of non-collapsed phloem and phloem with crystals, which were higher in the tolerant clones and in trees with score 0. The more resistant clones or samples with lower EPD scores exhibited a higher proportion of the regions of living phloem, phloem with CaOx crystals, and non-collapsed phloem. These results support the hypothesis that an increased proportion of STE collapse will occur concurrently with elevated EPD scores and are the basis for an ongoing histometric approach.  application/pdfbark anatomydiebackEPDEucalyptusphloem anatomyplanted forestfolyóiratcikkOpen AccessInternational Journal of Horticultural Sciencehttps://doi.org/10.31421/ijhs/31/2025/15419International Journal of Horticultural Science131Int. j. hortic. sci.2676-931X