Background and aims – This study investigates the phenotypic plasticity of Wittrockia cyathiformis (Bromeliaceae), an endemic species of the Atlantic Rainforest, with the aim of evaluating its morphological variation in relation to different life forms and forest types, specifically Dense Ombrophilous Forest and Mixed Ombrophilous Forest.

Material and methods – Field collections were conducted in State Conservation Units and Campos Gerais National Park in Paraná during 2022 and 2023. We measured vegetative morphometric parameters of six to eight bromeliads for each life form (epiphytic, saxicolous, and terrestrial) in each forest type, totalling 43 specimens, with 22 from Dense Ombrophilous Forest and 21 from Mixed Ombrophilous Forest. Additionally, we assessed the national conservation status of the species in Brazil.

Key results – The different forest types of the Atlantic Forest exert a greater influence on the phenotypic variation of W. cyathiformis than life forms, with only leaf sheath length being greater in epiphytes and smaller in terrestrials. On the other hand, significant variations in leaf morphometry, such as leaf width and spine size, were strongly associated with the bioclimatic conditions of each forest type. Specimens from Dense Ombrophilous Forest exhibit characteristics typical of species adapted to warm and humid environments, with broader leaves, whereas those from Mixed Ombrophilous Forest have narrower leaves and smaller spines.

Conclusion – The different life forms of this species do not result in significant morphometric changes. However, its phenotypic plasticity is strongly influenced by the different forest types, which may favour adaptation to variable environmental conditions. Despite this adaptive capacity, W. cyathiformis is classified as endangered (EN) in its area of occupancy in Brazil. The ongoing habitat loss highlights the need for conservation measures to ensure the long-term persistence of its populations.

adaptive plasticity, bromeliad adaptation, climate-driven traits, leaf morphometrics, morphological variation

Phenotypic plasticity (PP) refers to an organism’s capacity to undergo morphological, physiological, or behavioural adjustments in response to environmental stimuli. In bromeliads, as well as in many other angiosperms, PP is expressed through variations in the shape, size, and number of vegetative and reproductive structures, serving as a critical adaptive mechanism. This plasticity allows these plants to thrive in diverse and often challenging environments, meeting the physiological demands imposed by their habitats (Givnish 1979; Neves et al. 2019).

While extensive research has explored the effects of environmental factors such as temperature, precipitation, and geographical distance on PP across various plant species globally (e.g. Royer et al. 2009 (Aceraceae); Peppe et al. 2011 (multiple angiosperm families); Moles et al. 2014 (angiosperms, gymnosperms, ferns and fern allies, and bryophytes); Wright et al. 2017 (multiple families); Liu et al. 2021 (Pottiaceae)), studies focusing specifically on PP within the Bromeliaceae family, particularly in relation to bioclimatic and phytogeographical variations, remain limited (Chaves et al. 2018; Neves et al. 2019). This gap in literature underscores the need for further research, which our study aims to address by investigating the PP of Bromeliaceae, thereby contributing to a deeper understanding of adaptive strategies in this diverse plant family.

The Brazilian Atlantic Forest is renowned for its remarkable biodiversity and high levels of endemism, making it a global hotspot for conservation efforts (Myers et al. 2000). Unfortunately, more than 75% of its original extent has been lost due to human activities (Myers et al. 2000; Ribeiro et al. 2009). Among the unique endemic species found in this region is Wittrockia cyathiformis (Vell.) Leme, a tank bromeliad that occupies a variety of habitats, including rocky outcrops, terrestrial substrates, and epiphytic environments. This species is primarily distributed across the south-eastern and southern regions of Brazil, particularly within Dense Ombrophilous Forests (DOF) and Mixed Ombrophilous Forests (MOF) (Wanderley and Martins 2007; Tardivo 2023). The distinct forest typologies of the Atlantic Forest, such as MOF and DOF, provide an ideal context for studying the PP of W. cyathiformis, as each forest type presents unique phytogeoclimatic and climatic conditions (Struminski 2001; Maack 2012; Nitsche et al. 2019).

In the southern region of Brazil, MOF experiences a distinct seasonal pattern with a rainy season from October to March and a dry season for the remainder of the year, along with severe frosts and temperatures ranging from below 10°C in winter to over 20°C in summer (Maack 2012; Nitsche et al. 2019). Conversely, DOF in the same region is characterized by maritime influence and a warm coastal climate, featuring high humidity and precipitation levels averaging 3,700 mm annually (Struminski 2001; Maack 2012). This diverse array of environmental conditions offers a unique opportunity to investigate how W. cyathiformis adapts to its surroundings and exhibits PP in response to varying ecological factors.

As noted by Peppe et al. (2011), regions with higher annual mean temperatures tend to host angiosperms with elongated leaves relative to their width. Givnish (1984) further emphasizes that plants in warmer climates with limited water availability often develop leaves adapted to minimize water loss through evaporation, resulting in smaller leaf sizes compared to those in more humid environments. However, observations specific to Bromeliaceae, particularly in the genus Vriesea Lindl., highlight the prevalence of narrow-leaved species in regions characterized by hot climates and high rainfall (Neves et al. 2019). Consequently, the influence of climate on leaf size determination in bromeliads remains ambiguous, and whether this corresponds to patterns observed in other angiosperms requires further investigation (Givnish 1984; Peppe et al. 2011; Wright et al. 2017; Neves et al. 2019).

Considering the ecophysiology of Bromelioideae, the subfamily to which W. cyathiformis belongs, water and nutrient absorption is primarily facilitated by peltate trichomes (scales) covering the leaf sheath portion in contact with the phytotelm, present on both the adaxial and abaxial surfaces, while the roots mainly serve absorptive and anchoring functions (Benzing 2000). Epiphytic bromeliads rely on these scales, and tank species also use their leaves to accumulate water, ensuring their survival on phorophytes, as they lack direct access to nutrients and water in forest soil (Benzing 2000; Oliveira 2004). In tank bromeliad species, trichome density is generally higher in the leaf sheath area. Accordingly, water and nutrient absorption through the leaf is influenced by the presence, shape, and distribution of scales on the surface of the sheath in contact with the phytotelm (Benzing 2000; Stefano et al. 2008).

The primary objective of this study was to explore the PP of W. cyathiformis across the diverse environments of the Brazilian Atlantic Rainforest in the state of Paraná. We aimed to investigate how variations in environmental conditions, particularly differences in life forms (terrestrial, epiphytic, and saxicolous) and forest types (DOF and MOF), influence the morphometric patterns of this species. Specifically, we examined whether the same life form (e.g. epiphytes) displays different morphometric traits in DOF versus MOF, and how these patterns compare across three life forms.

Our hypotheses predict that terrestrial bromeliads may present smaller leaf sheaths and lower density of peltate trichomes due to their possible reliance on roots for nutrition and hydration, while epiphytic and saxicolous species may exhibit the opposite pattern. Furthermore, we anticipate that W. cyathiformis in MOF may exhibit morphological patterns adapted to water scarcity, developing more elongated leaves. In contrast, those in DOF are likely to display wider leaf blades, favoured by the high-water availability combined with elevated temperatures. Ultimately, this research aims to expand our understanding of how PP enables W. cyathiformis to adapt to the diverse environmental conditions of the Atlantic Rainforest, while also filling part of the gap in knowledge regarding phenotypic plasticity in Bromeliaceae, and contributing to broader discussions in ecology and evolutionary biology.

Our results demonstrate that the different forest types of the Atlantic Forest exert a greater influence on the phenotypic variation of W. cyathiformis than life forms (epiphytic, saxicolous, and terrestrial). Significant variations in leaf morphometry, such as leaf width, bromeliad height, and spine size, were strongly associated with the bioclimatic conditions of each forest type. In contrast, the analysis of W. cyathiformis specimens without considering forest type revealed that only leaf sheath length varied among different life forms. This suggests that life form alone has a limited influence on the PP of this species.

However, when analysing life forms between different forest types, we observed significant differences in several morphometric parameters, highlighting the importance of environmental conditions in shaping the morphology of W. cyathiformis. Although microenvironmental differences occur among epiphytic, saxicolous, and terrestrial forms, these conditions did not result in significant morphometric differences within the same forest type, reinforcing that broader environmental factors play a more decisive role in phenotypic variation.

Considering broadly the comparison between life forms, W. cyathiformis exhibits phenotypic variation only in leaf sheath length, which is greater in epiphytic specimens and smaller in terrestrial ones, while the number of trichomes showed no significant differences. These results differ from the literature (Stefano et al. 2008; Zorger et al. 2019) and do not fully support our initial hypothesis, which predicted that terrestrial bromeliads would have smaller leaf sheaths and a lower number of trichomes, possibly due to the use of roots for nutrient and water absorption from the soil. The absence of variation in trichome number may be associated with the ecophysiological and genetic characteristics of W. cyathiformis, which make its life forms less dependent on root absorption for survival (Smith and Downs 1979).

The absence of differences in the number of trichomes in W. cyathiformis highlights the plant’s ecophysiological plasticity, enabling its survival in different life forms without significant changes in trichome density, also suggesting a reduced reliance on nutrient and water absorption through roots in its terrestrial form. The discrepancy compared to other studies (Stefano et al. 2008; Zorger et al. 2019) that identified differences in trichome numbers between epiphytic and terrestrial forms suggests that adaptive responses may vary among species due to genetic and ecophysiological differences.

According to the Classification of Ecophysiological Types of Bromeliaceae (Benzing 2000), species in the subfamily Bromelioideae, such as W. cyathiformis, have terrestrial, saxicolous, or epiphytic life forms with well-developed leaf tanks. In these plants, the leaves function in absorption through the leaf sheath, while the roots primarily provide mechanical support and are conditionally absorptive. Based on morphometric parameters, terrestrial specimens do not appear to rely on distinct root-provided nutrition compared to other life forms. However, epiphytic specimens invest more in leaf sheath length, possibly to ensure greater accumulation and retention of water and debris in the leaf rosette, which are essential for their nutrition and hydration (Voltolini and Santos 2011).

However, Zorger et al. (2019), while studying epiphytic and terrestrial forms of Billbergia euphemiae É.Morren (Bromelioideae - Bromeliaceae), observed that epiphytic bromeliads exhibited a higher density of absorptive peltate trichomes on the abaxial surface. Given the scarcity of evidence and the contrast with other authors (Stefano et al. 2008; Zorger et al. 2019). Therefore, considering the scarcity of evidence and the contrast with other studies (Stefano et al. 2008, Zorger et al. 2019), we emphasize the need for research that integrates physiology, morpho-anatomy, and genetics of Bromelioideae, including multiple species and broad sampling, to elucidate the relationship between trichomes and ecophysiological adaptations in this group.

In the context of different forest types, our results support the initial hypothesis that specimens in the DOF have broader leaf blades, influenced by higher water availability and elevated temperatures. Distinct phenotypic patterns were observed between forest types: in DOF, bromeliads exhibit broad leaf blades and sheaths with large spines, whereas in MOF, the leaf blades are long but narrow, with smaller spines, a larger external diameter, and a higher number of leaves.

The sampled forest fragments exhibit distinct climatic characteristics typical of their respective forest types. According to climatic data from DOF in Paraná (Struminski 2001), temperatures range from approximately 18°C in the coldest months to 22°C in the warmest months. However, we observed notable seasonality and increased temperatures in the sampled areas of DOF, with this bioclimatic particularity being the main factor associated with the greater sheath width across the three life forms of the specimens in this forest type.

In the DOF areas of the Serra do Mar in Paraná, high temperatures and substantial rainfall predominate. According to Wright et al. (2017), it is common to find angiosperms with large leaves in environments where high temperatures and significant humidity coexist. The authors conducted a global analysis of 7,670 angiosperm species across various climatic zones and highlighted that species with broad leaves prevail in warm and humid environments due to their greater efficiency in thermal regulation through transpiration. These climatic conditions influence plant morphology, demonstrating species adaptation to the local climate (Wright et al. 2017).

All plants perform evaporative cooling to reduce leaf temperature, which results in water loss through transpiration (Givnish 1984). For this mechanism to be efficient without leading to dehydration, it is essential that the plant has access to an adequate amount of water (Givnish 1984; Wright et al. 2017). In the DOF, where temperatures are high and precipitation is abundant, bromeliads have broad and large leaves, possibly as an adaptation to the high-water availability that allows greater efficiency in thermal regulation through transpiration. In contrast, in water-restricted environments such as the MOF, plants tend to develop narrower leaves, an adaptation that minimizes water loss (Givnish 1984; Wright et al. 2017).

Our results differ from those found by Neves et al. (2019), who studied the morphometry of Vriesea (Tillandsioideae - Bromeliaceae) in the Serra do Mar (DOF). While Neves et al. (2019) observed a predominance of specimens with narrow leaf blades and sheaths in regions with warm climates and high rainfall, our study focused on a different species, whose morphology exhibits distinct patterns under similar conditions. In another type of habitat, Lenzi et al. (2006) observed that the leaves of Aechmea lindenii (É.Morren) Baker var. lindenii (Bromelioideae - Bromeliaceae) are shorter, broader, and more coriaceous in herbaceous restinga environments, where they are fully exposed to solar radiation. On the other hand, individuals of the same species exhibit longer, narrower, and more membranous leaves in arboreal restinga areas, which provide more shade. These contrasts suggest that different bromeliad species or genera respond differently to phytological and bioclimatic variables, reflecting specific adaptations to each habitat.

The distribution of trichomes on the leaf sheaths is another phenotypic variation in W. cyathiformis that may have been influenced by the climatic variables of each forest typology. Smaller and asymmetrical trichomes do not cover the entire leaf surface in drier locations, as trichomes structured in this way, as observed in bromeliads in MOF, help promote water condensation on the leaves, allowing better circulation of droplets (Pierce 2007). Another interesting point regarding trichomes was the presence of scales showing signs of dehydration in the saxicolous specimen in MOF, a characteristic that occurs when the epidermis is not sufficiently moist in its habitat (Benzing 1976; Strehl 1983), corroborating the bioclimatic conditions observed in MOF.

The spines of W. cyathiformis varied greatly in size according to forest typology, both at the base of the leaf blade and at its apex, with bromeliads in DOF presenting more robust spines. According to Benzing (2000), the presence of spines on the leaf margins is a predominant characteristic in most Bromelioideae and many Pitcairnioideae. Specifically, ground-level plants in these subfamilies invest more in mechanical defences, such as spines, due to the significant predation they are subjected to, reducing physical damage to the plant (Benzing 2000). These relationships highlight how various ecological pressures shape morphological traits in bromeliads, allowing their adaptation to different habitats.

The high PP observed in our results may indicate a diverse gene pool in this species, allowing its local adaptation to variable environmental conditions (Ward et al. 2008; Townsend et al. 2010). However, climate change and the conversion of natural habitats into anthropogenic landscapes pose significant threats to biodiversity (Lemes et al. 2013; Ferro et al. 2014). Habitat alterations caused by human activities occur at a pace incompatible with evolutionary adaptations. Thus, despite the considerable adaptation of W. cyathiformis across different forest types in the Atlantic Forest, it is likely that the species will be adversely affected by these anthropogenic factors and intensified climate changes (Sala et al. 2000; Thomas et al. 2004; Dirzo et al. 2014).

Although W. cyathiformis is classified as Least Concern (LC) based on the extent of its occurrence, the species is considered Endangered (EN) due to its restricted area of occupancy. The ongoing loss and fragmentation of the Atlantic Forest threaten the integrity of its populations. Between 2018 and 2019, Paraná was the third state in Brazil with the highest deforestation rates in this biome (Vieira and Mendonça 2021). Fire also represents a constant threat, with 11.6 million hectares burned in the Atlantic Forest between 1985 and 2023, 39% of which were native vegetation, especially forests, which are highly vulnerable to fire as they are not adapted to it, resulting in significant biodiversity loss (Pinto et al. 2025). It is possible that areas previously inhabited by W. cyathiformis populations have already disappeared, making this an important focus of investigation for future studies.

The preservation of protected areas and remaining forest fragments, along with ecological corridors and the strengthening of fire prevention and control programs, play a crucial role in species persistence and the maintenance of their genetic diversity (Araújo and Bastos 2019; Pinto et al. 2025). Therefore, understanding the plasticity and phenotypic variations in species such as W. cyathiformis is essential for elucidating its ecology and supporting conservation strategies, especially considering its vulnerability to extinction threats (Kunin and Gaston 1997).

Our results demonstrate that the different life forms of W. cyathiformis have a limited influence on morphometric variation, with a significant difference only in leaf sheath length, which is greater in epiphytic specimens. The absence of variation in trichome number suggests that terrestrial specimens do not rely on differentiated root-based nutrition, reinforcing the importance of leaf sheaths in resource absorption. Additionally, distinct morphometric patterns were observed between the Atlantic Forest types, associated with the specific bioclimatic conditions of each ecosystem. The broad leaves in Dense Ombrophilous Forest (DOF) follow the typical pattern of angiosperms in warm and humid habitats but contrast with other bromeliads in similar environments, highlighting the uniqueness of the adaptive responses of W. cyathiformis.

We emphasize the need to expand studies on the PP, physiology, and genetics of Bromeliaceae, including multiple species and representative sampling. This effort is essential for understanding the interactions between morphology, ecology, and environmental factors, as well as providing a basis for effective conservation practices. The ongoing loss and fragmentation of the Atlantic Forest pose a critical threat to endemic species such as W. cyathiformis, whose area of occupancy is already considered endangered. We recommend future studies to assess the impact of these threats on the species’ populations, using the observed morphological adaptations as a foundation for management and conservation strategies. The preservation of natural habitats and the implementation of ecological corridors are urgent measures to ensure the survival of this and other vulnerable species.

This work was made possible by the financial support of the Coordination for the Improvement of Higher Education Personnel (CAPES). Thanks to research permit no. 46.21 granted by the Water and Land Institute (IAT) of Paraná. Special thanks to the State University of Ponta Grossa (UEPG) and its Herbarium (HUPG) for transportation and support in conducting field collections. We also thank the Laboratory of Genetics and Evolution (LAGEV) and the Multiuser Laboratory Complex at UEPG (C-LABMU) for all the infrastructure and support for the development of this research.