Structural differences in the secondary phloem suggest higher support and storage potential in stems than roots of Cytharexylum myrianthum Cham. (Verbenaceae)

Stems and roots are interconnected by their secondary phloem, a complex tissue that exhibits functional differences related to the anatomical structure of each organ. Here, we compared the structure of secondary phloem in mature stems and roots of Citharexylum myrianthum Cham. (Verbenaceae). We sampled the main stems at a height of 1.3 m and the roots at a depth of 0.5 m. We described both the qualitative and quantitative features of all secondary phloem cell types, and compared the quantitative features using a paired Student's t test. The same percentage of sieve tubes in the conducting phloem between the organs indicates a similar conducting efficiency between stem and roots, even though sieve tubes have wider diameters in the stems. Overall, stems had a higher portion of nonconducting secondary phloem than the roots, with a higher number of both parenchyma and sclerenchyma bands, likely indicating a higher storage and support potential of the phloem in stems.