2.1 Collection data

The wood of M. glomerata was collected by F. B. Guimarães on June 14, 2011, at the bank of the river known as “Rio do Peixe”, in an area cleared for the construction of the Small Hydroelectric Power Plant – PCH “Salto Góes”, in the municipality of Tangará, Santa Catarina, Brazil (Figure 1). The specimen measured 1.5 meters in height, and three wood discs were collected from the trunk at breast height. The voucher specimen (dried specimen and wood) was deposited in the FLOR Herbarium of the Federal University of Santa Catarina – UFSC, under the code FLOR0039662, and a wood slide was prepared. A duplicate was incorporated into the JOIw xylotheque collection. This histological slide was used to describe the wood presented in this study.

The Tangará region has a humid temperate climate with mild summers (Cfb), according to the Köppen-Geiger classification, characterized by moderate temperatures and well-distributed precipitation throughout the year, with no dry season (Epagri, 2003). The predominant phytophysiognomy is Mixed Ombrophilous Forest, belonging to the Atlantic Forest biome (SOS Mata Atlântica, 2018). 

Figure 1 – Collection site location map 

Source: Authors (2026). UTM coordinate system, SIRGAS 2000 datum, Zone 22S. Consulted source: Google Earth Pro, IBGE

2.2 Preparation and anatomical description

Anatomical preparations followed standard wood anatomy techniques (Johansen, 1940; Sass, 1951; IAWA, 1989). The specimens were softened by boiled water and glycerin (Ferreirinha, 1958). Sections were cut in the usual planes: transverse, radial longitudinal, and tangential longitudinal in a sliding microtome. They were clarified with sodium hypochlorite (NaClO), rinsed with distilled water, stained with safranin and astra blue, and dehydrated in an increasing ethanol series (Kraus & Arduin, 1997). Permanent slides were mounted using synthetic resin as described by Paiva et al. (2006). The anatomical description followed the terminology recommended by the IAWA Committee (1989).

Microscopic structures were observed using an Olympus CX31 transmitted light microscope. Mineral inclusions were examined using polarized light with the same equipment. Photomicrographs were taken using an OPTICAM O600RT photomicroscope. Quantitative data are presented as (min – mean ± standard deviation – max).

The wood anatomy of Myrcia glomerata is described and illustrated below (Figure 2).

Growth rings: boundaries distinct, marked by the thickening of radial walls of fibers.

Vessels: diffuse porosity; diffuse arrangement; exclusively solitary; simple perforation plates; intervessel pits alternate, predominantly small, occasionally minute (3.91–5.95 ± 1.03–7.39 µm); vessel-ray pits with distinct borders, similar to intervessel pits in size and shape throughout the ray cell; mean tangential diameter of vessel lumen between 50 and 100 µm (50.47–77.52 ± 19.28–133.38 µm); frequency of 5 to 20 vessels/mm² (5–9.3 ± 2.59–14);

Tracheids and fibers: presence of vasicentric tracheids with areolate pits; fibers with simple to minutely bordered pits; fiber wall thickness ranges from thin to thick in earlywood and becomes thicker in latewood.

Axial parenchyma: apotracheal diffuse; diffuse-in-aggregates; in tangential lines one cell wide and occasionally more than three cells wide.

Rays: one to three cells wide (7.90–18.54 ± 4.45–28.67 µm), most frequently 2 cells; height below 1 mm (112.06 – 175.37 ± 41.66 – 276.96 µm); heterocellular, with body composed of procumbent cells with over 4 rows of upright and/or square marginal cells; more than 12 rays per millimeter.

Mineral inclusions and other deposits: prismatic crystals occurring in non-chambered axial parenchyma cells, druses occurring within fibers; presence of crystals of other shapes (mostly small); and resins or gums present in radial parenchyma;

Suggestions of numbers and codes, according to the InsideWood format: 1p 5p 9p 13p 22p 24p 25p 30p 41p 47p 60p 69p 76p 77p 85p 86p 97p 102a 108p 116p 136p 137p 138p142p 144p 147p 152p. 

Figure 2 – Wood anatomy of Myrcia glomerata (Myrtaceae)

Source: Authors (2026). A) Diffuse porosity and distinct growth rings (arrow) in transversal section. B) 1-3 seriate rays in tangential longitudinal section. C) Heterocellular rays in radial longitudinal section. D) Axial parenchyma in lines (yellow narrow) and lines up to three cells wide (black arrow). E) Vasicentric tracheids (arrow). F) Vessel-ray pits (arrow). G) Druses (arrow). H) Crystals of other shapes (arrow). I) Prismatic crystals (arrow)

The results of this study confirm anatomical characteristics widely reported for the Myrtaceae family, such as simple perforation plates, vestured pits, vasicentric tracheids, thick-walled fibers, and heterocellular rays (Record & Hess, 1949; Dias-Leme et al., 1995), as well as the occurrence of solitary pores and apotracheal axial parenchyma (Metcalfe & Chalk, 1972; Santos & Marchiori, 2011). Record & Hess (1949) also mention the absence of spiral thickenings in vessels, except in two species of Myrceugenia. However, some divergences and particularities were observed, highlighting anatomical variations within the genus Myrcia, as discussed below.

The absence of spiral thickenings is common in tropical plants, as reported by Alves & Angyalossy (2000), whose study showed that only 2% of the 491 evaluated species presented such a feature. Within the Myrtaceae family, spiral thickenings were observed in only 33 of the 144 species studied by Schmid & Baas (1984) and in 1 of the 31 species analyzed by Dias-Leme et al. (1995).  

Diffuse porosity was reported in all 24 species of the Myrtaceae family (genera Myrciaria, Neomitranthes, Plinia, and Siphoneugena) evaluated by Santos et al. (2013), which aligns with our findings, as well as in nine species of the genus Eugenia analyzed by Santos, Marchiori, and Siegloch (2014), all belonging to Myrtaceae.

Vasicentric tracheids are structures adjacent to vessels that act as a subsidiary conduction system in the event of vessel embolism, increasing hydraulic safety. Therefore, their presence is more common in water-limited areas (Carlquist, 1985). The presence of such structures in the species studied here suggests that even in riparian forests with well-distributed rainfall throughout the year, water availability may show microvariations due to alluvial soil compaction or subtle seasonal fluctuations in the water table, for example.

Heterocellular rays, composed of different cell types, reflect a primitive phylogenetic condition among woody angiosperms (Kribs, 1935; Baas, Wheeler & Chase, 2000). This feature was reported in Campomanesia xanthocarpha Berg., Eugenia pyriformis Cambess, Myrcia retorta Cambess, and Plinia peruviana (Poir.) Govaerts, all from the Myrtaceae family (Stange et al., 2018), as well as in 31 species representing four genera of the subtribe Myrciinae (Calyptranthes, Gomidesia, Marlierea, and Myrcia) (Dias-Leme et al., 1995), indicating that heterocellular rays represent a common trait across the family.

The presence of distinct growth rings is commonly found in species from temperate climates but is not typical in most tropical woody species (Alves & Angyalossy, 2000; Wheeler et al., 2007) nor in most Myrtaceae species (Dias-Leme et al., 1995). However, it has been reported in Myrcia bombycina (O.Berg) Niedenzu (Marchiori & Santos, 2009) and Myrcia myscrophilla Kiaersk (Silva et al., 2024). Growth ring formation is related to cambial activity in response to environmental factors such as rainfall and temperature (Tomazello-Filho, Botosso & Lisi, 2001). Diffuse porosity, in turn, is commonly found in most tropical species (IAWA, 1989).  

The predominance of solitary vessels was described for several species in the Myrtaceae family by Stange et al. (2018) and Dias-Leme et al. (1995), which agrees with the findings of this study. 

Our findings of prismatic crystals in subdivided chambers of the axial parenchyma, as well as resins or gums in the radial parenchyma, differ from the description by Marchiori & Brum (1997), who reported the absence of crystals or other materials in the wood parenchyma. Dias-Leme et al. (1995) pointed out that the presence of crystals in the parenchyma is a common characteristic in the genus Myrcia, recorded in 10 of the 14 species evaluated. The presence of these crystals is associated with functions such as physical protection, calcium salt storage, oxalate removal from the metabolic system, and light organization during photosynthesis (Franceschi & Nakata, 2005).

Plasticity in the formation — or absence — of crystals may be linked to calcium regulation in plants. Under excess calcium conditions, the crystals appear to play a role in calcium sequestration in adjacent cells. However, when calcium becomes scarce in the environment, the crystals dissolve, enabling growth and metabolic maintenance of the plant (Nakata, 2012).

Crystal formation is also influenced by urbanization, acting as a response to exposure to gaseous pollutants. Plants act as biological filters, helping to remove pollutants and maintain ionic balance, as well as incorporating heavy metals into oxalate crystals, as demonstrated by Alves et al. (2008) in Eugenia uniflora L. (Myrtaceae) exposed to urban pollution in São Paulo, Brazil.

Thus, the observed divergence may be explained by possible ontogenetic, environmental, or methodological differences. Although the size and quantity of crystals may vary among different taxa, their shape and location within a taxon are usually specific and may be considered taxonomic features (Franceschi & Nakata, 2005).

The presence of alternate intervessel pits was reported in nine species of the genus Eugenia studied by Santos, Marchiori, and Siegloch (2014), all belonging to the Myrtaceae family. Intervessel pits were also described in 26 species of the Myrtaceae family investigated by Santos (2012), including two species from the genus Myrcia: M. bombycina (O.Berg) Niedenzu and M. selloi (Spreng.) N.Silveira. However, the study by Marchiori and Brum (1997) reports the absence of these structures in Myrcia glomerata, which differs from our findings and represents an unusual observation within the Myrtaceae family. However, the absence or limited visibility of intervessel pits is expected in species with exclusively solitary vessels, as vessel contacts are infrequent or only occasional (Esteban et al., 2024).

A higher number of intervessel pits increases the likelihood of leaky pit membranes, facilitating embolism propagation; which acts as an adaptive response to drought (Wheeler et al., 2005; Christman et al., 2009; Levionnois et al., 2021). Although structural variations in intervessel pits—such as differences in size and wall thickness—are well documented and appear to reflect responses to environmental conditions or the ontogenetic stage of the plant (Wheeler et al., 2005; Christman et al., 2009; Levionnois et al., 2021), no study was found that reported plasticity regarding the complete presence or absence of these pits within individuals of the same species. This makes the discrepancy observed in Myrcia glomerata particularly notable and inspires further investigation.

This study contributes to the anatomical understanding of the wood of Myrcia glomerata, expanding knowledge about its structural characteristics and comparisons with other species of the Myrtaceae. The observations made indicate that the anatomy of this species follows many of the typical patterns of the family, such as the presence of solitary vessels, vasicentric tracheids, and heterocellular rays, in addition to characteristics less common in tropical species, such as distinct growth layers. The analysis also revealed the unprecedented presence of prismatic crystals in the axial parenchyma and resins or gums in the radial parenchyma, which differs from previous studies and may suggest specific adaptations to the environment in which the plant occurs.

The study also inspires future research on anatomical variations within the genus Myrcia, mainly due to the differences found in comparison with previous studies. These findings may contribute both to the understanding of the plant and to the use of its natural resources. 

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