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Historical review of terminology applied to cambial variants in Nyctaginaceae

Citation

L. Cunha Neto, Israel (2021), Historical review of terminology applied to cambial variants in Nyctaginaceae, Dryad, Dataset, https://doi.org/10.5061/dryad.w9ghx3fn1

Abstract

Premise of research. The alternative patterns of secondary growth (vascular cambial variants) in stems of Nyctaginaceae are outstanding and has been widely investigated since late 19th century. However, there are controversial interpretations in the literature regarding the existence of one or two types of cambial variants (successive cambia vs. interxylary phloem). Thus, this study aims to explore the morphological diversity of stems in Nyctaginaceae, to unravel the real nature of the cambial variant present in most species of the family.

Methodology. Altogether we analyzed 60 species, focusing on 18 from 12 genera, which were used for the developmental studies. Anatomical and ontogenetic features were characterized from images produced by standardized plant techniques for macro and microscope analyses.

Pivotal results. Our analyses reveal that most species of Nyctaginaceae present stems with polycyclic eustele, which later develop a single cambium that produces secondary xylem and secondary phloem at unequal rates along the stem circumference. This unusual activity results in the absence of a regular cylinder and in the formation of secondary phloem strands (surrounded by conjunctive tissue) which are embedded within the secondary xylem. In cross-section, adult stems can be characterized by having different arrangements (i.e., phloem islands, patches, concentric bands), which results from difference in rates of phloem and conjunctive tissue forming the strands. The cambial variant in these stems are described as interxylary phloem, as similarly observed in other eudicot lineages.

Conclusions. Our examination of the stem development of Nyctaginaceae confirms the presence of interxylary phloem, which has been overlooked in the family since most studies reiterates the descriptions of successive cambia as the common pattern of cambial variant within the family. These findings emphasize the importance of developmental studies to further our understand of stem macromorphologies and highlight the complexity and diversity of stem architectures in Nyctaginaceae.

Funding

FAPESP - Fundação de Amparo à Pesquisa do Estado de São Paulo, Award: 2017/17107-3