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<p class="Normal1"><strong>Background.</strong> Distinguishing species and populations in Crassulaceae is challenging because of the morphological variability and inter-specific hybridization. Currently our understanding of the morphological and anatomical features in <em>Echeveria</em> is poor, and therefore it is difficult to delimit species, and morphotypes within the species. </p><p class="Normal1"><strong>Question.</strong> Our objective was to describe the foliar anatomy and the shape of accessions in <em>E. gigantea.</em> We used <em>E. gibbiflora</em>, another species in the series as a comparison group. Comparing the two species allowed us to evaluate the relationship between anatomy and morphology in <em>E. gigantea</em>.</p><p class="Normal1"><strong>Methods. </strong>We performed a survey of anatomical features in seven accessions of <em>E. gigantea</em>, and one accession of <em>E. gibbiflora</em>. We obtained epidermal prints, leaf sections, performed geometric and morphometric analyses.</p><p class="Normal1"><strong>Results. </strong>We found that 65  % of the anatomical traits are heterogeneous among the taxonomic units. Our analysis showed that <em>E. gibbiflora</em> and some <em>E. gigantea </em>accessions share extensive anatomical similarities. There was variation within the <em>E. gigantea</em>, suggesting that at least one of the accessions is an independent taxonomic group. The traits with the largest contribution to variation between the groups were related to the epidermis, the hypodermis, the type of vascular bundles and the collenchyma associated to the vascular bundles. In addition we quantified the variation in leaf shape. Interestingly, we found correlations between the organ shape and anatomical traits.</p><p class="normal"><strong>Conclusion. </strong>These analyses provide information about traits towards the morpho-anatomical definition of <em>E. gigantea</em> variation and suggest developmental correlation yet to be explained.</p>

Exploring the anatomical variability along the stem of cacti requires obtaining high-quality thin sections from hard and soft tissues. Several embedding, infiltration, and sectioning methods have been applied mainly to investigate the harder stem base of cacti, where thin cross-sections are relatively easy to obtain. However, analyzing the variation of anatomical features along cacti stems remains a challenge. Specifically, at the tip of cacti stems, the soft and water-rich dominant tissues are difficult to infiltrate. Here we show results obtained by adapting polyethylene glycol (PEG) infiltration techniques and present a step-by-step description of a fast and hazardous chemical-free method that allows successful cross-sectioning. This infiltration technique may provide a tool to further explore and quantify xylem anatomical trait variation along stems of a wide range of succulent-stemmed taxa.

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Análisis morfométrico del grupo Selenicereus vagans (Cactaceae: Hylocereeae) con base en la anatomía del tallo Morphometric analysis of the Selenicereus vagans group (Cactaceae: Hylocereeae), based on stem anatomy