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Stem anatomy diversity in Iresine (Amaranthaceae s.l.): an ecological interpretation

Zumaya-Mendoza, Silvia, Aguilar-Rodríguez, Silvia, Yáñez-Espinosa, Laura, Terrazas, Teresa
Revista brasileira de botânica 2019 v.42 no.2 pp. 329-344
Iresine, comparative study, growth rings, habitats, longitude, meristems, multivariate analysis, periderm, photosynthates, pith, rain, shrubs, surveys, temperature, trees, wood
Iresine is an American genus that belongs to Amaranthaceae s.l. To understand its stem anatomy and correlation with the habit and habitat, a comparative study was carried out. We present the most extensive stem anatomical survey of Iresine to date. Our observations agree with wood descriptions for other Amaranthaceae having simple perforation plates, intervessel pits alternate and nucleated fibers. Few species showed distinctive growth rings. Rays are heterocellular, multiseriate with meristematic centers. The occurrence of rays with meristematic centers is not related to habit or habitat, but suggests that water and photosynthates movement is complex through the axial–radial system. Species studied have successive cambia in concentric bands or patches. Seven species have distinctive characters as for I. latifolia (M.Martens & Galeotti) Hook.f. with two or three pairs pith bundles, I. rzedowskii Zumaya, Flores Olv. & Borsch with a thick periderm and I. cassiniiformis S.Schauer with lignified pith. Not all quantitative wood features follow the trends expected with habit but significant differences exist (P > 0.05) for some as fiber length. The tree species has the widest vessel diameter (81 µm) and the longest fiber length (570 µm), and shrubs show the highest variation. Canonical correlation analysis allowed to identifying that mean annual temperature, longitude and annual rainfall have an impact in the wood of Iresine species, especially in vessel and fiber wall thickness, intervessel pit diameter and fiber length. Iresine wood appears to be more susceptible to changes of mean annual temperature and precipitation showing its plasticity.