Rocks constitute the foundational material substrate for soil formation and development, playing a pivotal role in shaping soil types and determining their physicochemical properties (Hu and Gu, 2022). This divergence in soil properties is reflected in the distribution of CDPs: Dionysia involucrata thrives on granite rock cliffs (Nowak et al., 2014), while Clematis acerifolia is predominantly found on limestone cliffs (Zhao et al., 2023a). Although the distribution of CDPs is shaped by a multitude of factors, including temperature, climate, altitude, microenvironments, and microbial communities, soil type emerges as a critical and overarching determinant. For example, plants growing in limestone soils must contend with neutral to alkaline conditions, high concentrations of calcium, magnesium, and carbonates, limited availability of phosphorus, iron, and zinc, and frequent drought stress (Flores-Galván et al., 2024). In contrast, granite soils are typically acidic, rich in potassium and silicon, but deficient in organic matter and phosphorus, creating drier and less fertile conditions for plant growth (Hu and Gu, 2022).

Although extreme environments have traditionally been considered inhospitable to fungal survival (Gostinčar et al., 2022), growing evidence demonstrates that fungi not only persist but thrive in such conditions, including extremely cold habitats (Gunde-Cimerman et al., 2003) and arid deserts (Santiago et al., 2018). This raises an intriguing question: do cliffs, as another type of extreme environment, also harbor diverse and functionally significant fungal communities? In 2022, environmental DNA metabarcoding (eDNA) was used to examine the fungal diversity on three cliffs in Spain, revealing the presence of a remarkably diverse fungal community in these habitats. Notably, most of the fungi identified were saprotrophs, which play a crucial role in decomposing dead plant material and recycling nutrients back into the cliff crevices, thereby facilitating plant growth and sustaining the cliff ecosystem (Franz-Sebastian and March-Salas, 2022). In turn, host plants provide C sources that may enhance the survival of fungi. A study that compared two types of cliff soils- those with and without CDPs- found no significant differences in fungal amplicon sequence variant richness or composition between the two types of soil. The similarity in fungal communities may be owing to several factors. First, saprotrophic fungi in cliff habitats may prefer organic matrix components over plant material (Algora Gallardo et al., 2021). Secondly, the harsh selection pressures of the cliff environment may have a stronger influence on the fungal communities than the presence of host plants.

A series of studies have explored Festuca rubra subsp. pruinosa, a perennial plant that grows on sea cliffs, and its fungal endophytic microbiome. The microbial composition of the rhizosphere was analyzed, and it revealed a total of 135 fungal species, with Diaporthe and Fusarium identified as core components of the microbiome (Pereira et al., 2019). It has been reported that these two fungal species promote plant growth and development. The mechanisms by which Diaporthe atlantica supports plant growth could include the breakdown of dead roots and other organic matter into N sources and simple carbohydrates, which help the host plants to access nutrients, as well as the production of indole-3-acetic acid (IAA), which stimulates root growth (Toghueo et al., 2023) ( Figure 1b ), while Fusarium oxysporum can promote the growth of Festuca rubra subsp. pruinosa leaves and roots, as well as significantly reducing the content of Na⁺ in its leaves, which may be related to the mechanisms of salt tolerance in the plants (Pereira et al., 2021).

The availability of cliff water is primarily determined by rainfall patterns and the porosity and permeability characteristics of rock formations (Aronne et al., 2018). Furthermore, the direction of cliff crevices significantly influences surface water distribution, which subsequently affects seed germination and seedling establishment during the initial developmental stages of CDPs. An 18-year study on Thuja occidentalis clearly illustrated these differences. In horizontal crevices, more seeds and water accumulate on the surface of the soil, which results in a higher rate of seed retention and germination ( Figure 1c ). However, the survival rate of these seedlings is low owing to the limited retention of water in these sites. In contrast, vertical crevices enable hydraulic pressure to channel rainwater down the cliff surface, which results in a greater amount of stable and available water. As a result, the seedlings in vertical crevices survive at higher rates, but the rates of seed retention and germination are lower. Additionally, the seedlings in horizontal crevices are more susceptible to disease and struggle to recover, while in vertical crevices, rockfalls are another cause of seedling mortality (Matthes and Larson, 2006).

CDPs have evolved sophisticated adaptive strategies at multiple biological levels to survive in harsh cliff environments. At the organismal level, CDPs typically exhibit dwarf morphology or adopt prostrate growth forms (Itoh et al., 2024). Leaf morphological adaptations include reduced size, increased thickness, and waxy cuticles (Radić et al., 2005; Spanò et al., 2013; Pérez-Diz et al., 2023), accompanied by anatomical modifications such as enhanced palisade parenchyma development (Radić et al., 2005), enlarged epidermal cells, specialized water-storing parenchyma, and increased stomatal density (Spanò et al., 2013). Specific adaptations of roots include the development of rhizome structures (Liu et al., 2007) and suberin deposition in root exdermis (Yang et al., 2020). Furthermore, CDPs exhibit stage-specific developmental adaptations, as exemplified by Primula palinuri Petagna, which develops specialized hypocotyl hairs during seedling establishment to enhance water absorption capacity (De Micco and Aronne, 2012). These multifaceted adaptations help CDPs adapt to the water- and nutrient-limited environment.

Recent studies have revealed that approximately 5%-10% of vascular plant species exhibit specific soil preferences (Zhao et al., 2024), a phenomenon particularly evident in certain CDPs with strict edaphic requirements. Among these, Primulina species demonstrate remarkable soil specificity, with most taxa being exclusively associated with limestone-derived soils. This adaptation to calcareous substrates is facilitated through specialized physiological mechanisms, particularly in calcium metabolism. These plants have evolved the capacity to store calcium primarily as calcium pectate within their cell walls, a strategy that serves dual protective functions: maintaining membrane stability and preventing cytoplasmic damage through extracellular calcium precipitation (Qi et al., 2013). These unique calcium assimilation and compartmentalization mechanisms likely represent fundamental evolutionary adaptations that enable their survival in specialized soil habitats.

CDPs have evolved diverse strategies to cope with drought stress in cliff environments. A notable example is Pleurostima purpurea, which exhibits sophisticated drought avoidance mechanisms. This species initiates stomatal closure at relatively high leaf water content (up to 90%) during moderate drought conditions. This adaptive mechanism establishes a critical temporal buffer that enables rapid restoration of leaf physiological functions upon sudden rehydration of the soil (Aidar et al., 2010). Furthermore, CDPs employ multiple physiological adaptations to mitigate drought stress. These include the upregulation of antioxidant enzyme activities and enhanced biosynthesis of osmoregulatory compounds, which collectively mitigate oxidative damage by scavenging reactive oxygen species (ROS) and maintaining cellular osmotic balance (Yang et al., 2020). Additionally, CDPs regulate their phytohormone profiles in response to drought conditions, particularly through significant accumulation of abscisic acid (ABA), which serves as a key signaling molecule in drought stress responses (Villadangos and Munné-Bosch, 2024).

Plants exhibit remarkable adaptability to cliff habitats through strategic growth adjustments. A prime example is Sempervivum tectorum, which demonstrates drought adaptation by minimizing growth and reducing asexual reproduction during dry seasons (Villadangos and Munné-Bosch, 2024), thereby effectively conserving energy. Similarly, P. palinuri has developed an adaptive mechanism where its leaves, despite lacking specialized drought-resistant structures, undergo desiccation during summer droughts in their natural habitat (De Micco and Aronne, 2012). Furthermore, CDPs have evolved slow growth strategies to cope with water- and nutrient-deficient soils, this slow growth strategy may also be related to the low N utilization of CDPs (Pérez-Diz et al., 2023). As demonstrated by Zhao et al. (2023a), these plants reduce their growth rate to alleviate environmental stress, showcasing an efficient adaptation to their challenging habitat conditions.

Seedling establishment represents a critical yet understudied phase in the life cycle of CDPs (Aronne et al., 2023). Despite their rarity in natural populations, seedlings play a crucial role in maintaining genetic diversity (Zhao et al., 2023a). The cliff environment poses multiple challenges to seedling survival, including water scarcity, temperature extremes, intense solar radiation, pathogen threats, and spatial limitations. Even when moisture conditions permit seed germination, they often prove inadequate to support extensive seedling growth. While climatic factors significantly influence early seedling development, their impact diminishes with plant maturation (Matthes and Larson, 2006), likely due to the development of stress-tolerant structures. This developmental adaptation is particularly evident in P. palinuri, where mature plants develop a suberized root exodermis that prevents water loss. Their rhizomes demonstrate remarkable resilience, capable of continued growth after mechanical damage from environmental forces like strong winds. Additionally, the accumulation of starch in root cells enhances their drought tolerance and other environmental resistances. In contrast, seedlings lack these protective mechanisms, making them particularly vulnerable to environmental stresses compared to mature plants (De Micco and Aronne, 2012).

CDPs have evolved remarkable reproductive strategies to ensure species survival in challenging habitats. Sexual reproduction, particularly through pollination, represents a critical yet vulnerable stage in their life cycle (Li et al., 2018), with successful seed production being its ultimate objective. Despite the ecological significance of studying these reproductive adaptations, research is often hindered by the inaccessible nature of cliff habitats. CDPs employ two primary strategies to optimize seed production. First, many species utilize a mixed mating system combining cross- and self-fertilization ( Figure 2a ). This dual approach, observed in species such as Lonicera oblata (Wu et al., 2022) and Opisthopappus species (Wang et al., 2023), provides both genetic diversity through cross-fertilization and reproductive assurance through self-fertilization (Wang et al., 2023). Furthermore, self-fertilization offers another advantage of increasing homozygosity and facilitating the fixation of adaptive traits such as salt tolerance and late flowering (Itoh et al., 2024). Secondly, CDPs have developed adaptive mechanisms for reproductive organ development. Taihangia rupestris exemplifies this adaptation through temperature-dependent differentiation of floral structures. This species produces both hermaphroditic and unisexual flowers, with stamen development at lower temperatures (1-6°C) before April, optimizing pollen production, while pistil development occurs at higher temperatures (6-26°C), ensuring seed maturation by June (Lu et al., 1995, 1996). However, sexual reproduction in CDPs faces significant environmental challenges. Habitat fragmentation, resulting from both natural processes (creating ecological islands) and human activities, disrupts pollen and seed dispersal (Colas et al., 2001; García et al., 2012). Additionally, extreme weather conditions, including temperature fluctuations, intense solar radiation, and strong winds, can adversely affect flowering phenology, pollen viability, and pollinator activity, ultimately impacting pollination success and seed production (Wu et al., 2022).

In addition to sexual reproduction, asexual reproduction is crucial for the survival of CDPs. Many CDPs, such as T. rupestris and Oxyria sinensis, reproduce asexually through rhizomes, which are particularly important in crevices ( Figure 2b ). These crevices are often interconnected and form a network that promotes the growth and spread of the plants (Lu et al., 1995; Tang et al., 2004; Liu et al., 2007). Rhizome-based reproduction offers several advantages that enhance the plants’ ability to adapt to harsh environments. First, rhizomes enable the formation of extensive clonal colonies, which enables the plants to expand their populations through physiological integration. Secondly, rhizomes help the plants to access more fertile microsites and select the most favorable cliff crevices as they grow. Finally, the interconnectedness of rhizomes can protect the plants from rock fall and erosion, which improves their rates of long-term survival (Liu et al., 2007). In summary, rhizomes are essential for the CDPs to acquire resources, explore suitable microhabitats, expand clonal colonies on cliff surfaces, and contribute to the overall stability of cliff ecosystems.

Drought represents a defining characteristic of cliff habitats, and the drought resistance mechanisms in CDPs involve complex physiological processes regulated by multiple genes. Recent studies have identified several key genetic components contributing to drought adaptation. In Dendrobium catenatum, the FAR (Fatty Acyl-CoA Reductase) genes encode essential enzymes for plant wax biosynthesis, enhancing drought resistance (Ren et al., 2023). Furthermore, transcriptomic analysis of Opisthopappus taihangensis roots under drought stress has revealed the upregulation of multiple gene families associated with various protective mechanisms. These findings can be attributed to ABA accumulation, proline and trehalose synthesis, SOD and POD activity, suberin deposition (Yang et al., 2020).

Salt stress constitutes another significant environmental challenge in cliff ecosystems. Opisthopappus species have developed sophisticated molecular adaptations, particularly through alternative splicing mechanisms such as skipped exons (SE) and mutually exclusive exons (MXE), to cope with saline conditions. Current research indicates that salt tolerance in these plants is mediated by genes primarily involved in protein phosphorylation, starch and sucrose metabolism, and plant hormone signal transduction (Zhang et al., 2023; Thalmann and Santelia, 2017; Han et al., 2024).

Genetic diversity is crucial for species survival and environmental adaptation (Ding et al., 2015; George et al., 2009). High genetic diversity enhances evolutionary potential, while low diversity limits adaptability to environmental changes (Binks et al., 2015). For example, some CDP species, like C. acerifolia (López-Pujol et al., 2005; Zhao et al., 2023a), Asperula naufraga (Valli et al., 2021), and Antirrhinum subaeticum (Jiménez et al., 2002), exhibit low genetic diversity, while others, such as O. taihangensis (Guo et al., 2013) and T. rupestris (Tang et al., 2010; Duan, 2013; Wang et al., 2011; Li et al., 2018), show higher diversity. Moreover, genetic diversity is influenced by factors such as cliff crevice variability (such as differences in size, depth, and microclimatic conditions), environmental pressures, seedling growth, pollen and seed dispersal, and reproductive biology (George et al., 2009; Neri et al., 2021; Zhao et al., 2023b). In China’s Taihang Mountains, C. acerifolia, T. rupestris, and O. taihangensis coexist but display varying genetic diversity levels. C. acerifolia’s low diversity may result from limited seed dispersal and few wild seedlings (Zhao et al., 2023), whereas T. rupestris’s high diversity is likely due to its ancient origins and mixed reproductive strategies (Wang et al., 2011). Similarly, O. taihangensis benefits from wind and gravity-aided seed dispersal, enhancing its genetic diversity (Guo et al., 2013). Evaluating genetic diversity is essential for CDP conservation and management. However, current methods, such as isozymes (López-Pujol et al., 2005), ISSR (Guo et al., 2013), and simplified genome-derived SSRs (Zhao et al., 2023a), may not fully capture genetic diversity due to insufficient genomic data ( Figure 2c ). To overcome this limitation, future research should focus on generating comprehensive genomic data for CDPs, which will allow for a more accurate assessment of their genetic diversity.

Genomic data have significantly advanced our understanding of the population and evolutionary genetics of plants. The genomes of CDPs provide critical insights into their adaptive mechanisms and serve as essential resources for genetic diversity research. Plant genomes include the nuclear, chloroplast, and mitochondrial genomes, and to date, eight CDP species have been sequenced ( Table 1 ). Chromosome-level genome sequencing is particularly valuable for accurately assessing genetic diversity, elucidating adaptation mechanisms, and guiding conservation strategies (Li W. G. et al., 2024). For instance, the genome sizes of Taihangia rupestris var. ciliata from the Taihang Mountains and Scaevola tacada from seaside cliffs are 769.5 Mb and 1.1 Gb, respectively (Li W. G. et al., 2024; Li et al., 2023). Both species exhibit a high abundance of long terminal repeat retrotransposons (LTR-RTs), suggesting these elements play a key role in their adaptation to extreme environments. T. rupestris var. ciliata, adapted to mountain cliffs, faces drought and cold stress. Its resilience is likely mediated by transposable elements (TEs), LTR-RTs, and oxidative phosphorylation genes (Li W. G. et al., 2024). In contrast, S. tacada, inhabiting seaside cliffs, endures intense light and salt stress, with the FAR1 gene (FAR-RED-IMPAIRED RESPONSE1) playing a crucial role in its coastal adaptation (Li et al., 2023). These findings highlight the importance of genomic studies in understanding CDP adaptation and informing conservation efforts.

The survival of CDPs is increasingly threatened by their highly specialized habitats, which are often fragmented and unstable (Clark-Tapia et al., 2021). Genetic diversity is critical for their long-term survival, serving as a key indicator of adaptability and evolutionary potential (Ding et al., 2015). Current methods for assessing genetic diversity, such as isozymes (López-Pujol et al., 2005) and molecular markers like SSRs (Zhao et al., 2023a) and SNPs (Ye et al., 2021), often rely on limited markers, potentially underestimating genetic variation. Furthermore, reference genomes for most CDPs remain unavailable ( Table 1 ), hindering comprehensive genetic analyses. The development of high-quality, de novo assembled genomes would provide robust genomic data, improving the accuracy of genetic diversity assessments and population structure analyses ( Figure 3a ). Such resources are expected to become more accessible with the decrease of sequencing cost, enabling deeper insights into CDP genetics. Sampling representativeness is another critical factor in genetic diversity studies. However, accessing CDPs for sampling is often risky and impractical (Zhou et al., 2021), and care must be taken to avoid collecting clones from the same crevice (Tang, 2004; Tang et al., 2004; Zhao et al., 2023a). Recent advancements in unmanned technologies have facilitated safer and more efficient observation and sampling of CDPs (Gao et al., 2024). Moving forward, user-friendly sampling methods and interdisciplinary collaboration will be essential for large-scale, comprehensive genetic diversity and taxonomic studies ( Figure 3a ). These efforts will enhance our understanding of CDP adaptation and inform effective conservation strategies.

In practical conservation efforts, it is essential to comprehensively consider the factors influencing the survival of CDPs ( Figure 3b ). Conservation strategies should not only focus on rare species but also encompass common CDPs, as they play critical roles in maintaining ecosystem stability and supporting biodiversity. These common species reduce rock erosion, support species colonization, and contribute to nutrient cycling through biomass decomposition, enriching the cliff ecosystem. Additionally, their abundance attracts pollinators, enhancing the reproductive success of both rare and common plants (March-Salas et al., 2023). Therefore, conservation strategies should adopt a holistic approach, prioritizing the preservation of the entire cliff ecosystem, including both rare and common species. It is noteworthy that rock climbing, a globally popular recreational activity, has the potential to disrupt cliff ecosystems, although studies investigating its impact on CDPs have produced inconsistent findings. Some studies indicate that climbing reduces vegetation cover, species richness, and alters ecosystem composition (Lorite et al., 2017; de Castro-Arrazola et al., 2021), while others find no significant effects (Boggess et al., 2017, 2021). These discrepancies may stem from varying climbing intensities (Boggess et al., 2017) or natural differences in cliff vegetation (Boggess et al., 2021). As a result, balancing recreational rock climbing with the preservation of cliff ecosystem integrity is very important in CDP conservation.

Ex situ conservation can be effectively achieved through the reintroduction of artificially propagated materials, such as seeds or seedlings, into native habitats or by establishing protected areas like botanical gardens. Usually, mature plants are often unsuitable for reintroduction due to their deep roots in unstable cliff crevices. Seeds, in particular, are ideal for propagation and protection, as they suffer less damage and are easier to handle (Liu D. Y. et al., 2023; Zhao et al., 2023b). The survival rate of reintroduced materials depends significantly on the specific location of cliff crevices chosen (Gao et al., 2024). A successful example is the reintroduction of Hubbardia heptaneuron in 2009, where seeds were used, and damp, dark areas near waterfalls with dense vegetation were identified as optimal conditions (Duvall et al., 2017). Furthermore, water management is crucial during artificial propagation, as CDPs typically thrive in arid environments (Li W. G. et al., 2024). Additionally, nutrient acquisition in CDPs may rely on fungi, which have substrate preferences, suggesting that nutrient availability influences their growth (Toghueo et al., 2023; Algora Gallardo et al., 2021). In summary, effective management of propagation materials and tailored substrate conditions are essential for the successful conservation of CDPs.

The drastic impacts of global climate change, including increased droughts, storms, and extreme temperatures (Lindenmayer and Laurance, 2016; Shinozaki and Yamaguchi-Shinozaki, 2024), are reshaping ecosystems worldwide. In response to these significant environmental changes, plants typically migrate to more suitable areas or undergo self-evolution to adapt to new conditions (You et al., 2024). On the one hand, CDPs have evolved into various ecological forms to survive harsh environments (Itoh et al., 2024) or variants (Yan et al., 2016). As climate change progresses, it is anticipated that CDPs will continue to evolve into even more diverse forms or potentially new species adapt to increasingly extreme conditions. Alternatively, habitat fragmentation owing to climate change, coupled with the specific habitat requirements, may hinder the ability of CDPs to naturally migrate through seed dispersal or asexual reproduction (Clark-Tapia et al., 2021). In such cases, artificial propagation techniques can assist in relocating the CDPs to more suitable environments. For instance, to address extreme drought conditions, artificial water supply systems could be utilized. The effects of rising temperatures could be mitigated by relocating the CDPs from low-latitude areas to cooler, higher-latitude regions. Ultimately, given the severity of global climate change, protecting the genetic resources of CDPs is of the utmost importance. Establishing specialized germplasm banks for these plants is a crucial strategy for safeguarding this unique and habitat-specific plant group.

Research on CDPs primarily focuses on their adaptation mechanisms to cliff environments and conservation efforts. However, due to the inaccessibility of cliff habitats and the slow growth rates of CDPs, observation and sampling remain challenging, leaving several areas understudied. First, Conducting long-term monitoring is an essential approach for studying cliff ecosystems, understanding plant-environment interactions, and conserving plant species. (1) Ecosystem networks: mapping plant-animal-microbe-habitat interactions; (2) Survival mechanisms: high-resolution phenotyping of stress responses to chronic/acute environmental stresses. (3) Conservation efforts: tracking habitat dynamics, soil-water parameters, and population viability under different conditions. Furthermore, effective implementation requires renewable-powered equipment and automated data workflows; Second, physiological mechanisms including nutrient utilization in depleted environments, water absorption and efficiency, overwintering strategies, root-microbe interactions in cliff crevices, photosynthetic characteristics, and shade tolerance are scarce. Third, molecular mechanisms, especially resistance-related genes, as well as lifecycle bottlenecks, are significantly lacking in most CDPs (Aronne et al., 2023).

The development of innovative technologies and tools presents promising solutions to current research limitations in CDP studies, serving as a pivotal direction for future investigations. These advancements should address cliff habitat challenges, such as energy-efficient real-time image acquisition systems for monitoring microhabitat dynamics during sustainable ecological observation; standardized laboratory cultivation protocols to obtain experimental materials for physiological studies; and molecular genetic transformation platforms enabling cellular-level exploration of stress adaptation mechanisms. Each technological pathway specifically counteracts the inaccessibility of cliff ecosystems and the slow growth constraints inherent to CDPs.

Interdisciplinary integration is also essential for studying CDPs and their unique habitats. Long-term monitoring demands technologies spanning microecology, engineering mechanics, drone systems, and AI-driven data analytics to automate environmental sensing in inaccessible terrains. Meanwhile, physiological investigations require convergence of ecology, soil science, and phenomics to decode nutrient dynamics and stress adaptation traits. At the molecular level, single-cell omics, epigenetics, and bioinformatics jointly map vertical-microclimate-induced gene regulation and stress signaling networks.