An Urban Refuge for Threatened Cacti: Diversity and Conservation of the Cactaceae Collection at FES-Cuautitlan Botanical Garden, UNAM

1. Introduction

Mexico ranks among the most biologically megadiverse countries on Earth, a distinction that is particularly evident within the family Cactaceae. With approximately 669 species distributed across its territory, of which nearly 78% are considered endemic, Mexico represents the primary center of diversification and origin of this family at the global scale [1,2]. The Cactaceae family comprises roughly 1480 species grouped in 157 genera [3], and its members are predominantly distributed in arid and semiarid regions of the Americas, with Mexico harboring the greatest species richness on the continent [4,5]. The high level of endemism observed in Mexico is attributable to the complex geological and climatic history of the country, which has generated a remarkable diversity of microhabitats, particularly across the Chihuahuan Desert, the Tehuacán-Cuicatlán Valley, and the Mexican Plateau [6,7].

Beyond their ecological significance, as keystone species providing food and shelter, cacti hold profound cultural and historical importance in Mexico. Their use by indigenous and rural communities spans millennia and encompasses nutritional, medicinal, ceremonial, and economic (Lem. ex Salm-Dyck) J.M.Coult., dimensions. Species such as Opuntia spp., Stenocereus queretaroensis (F.A.C.Weber ex Mathes.) Buxb., and Lophophora williamsii exemplify the deep intertwining of cactus with Mexican cultural heritage a[1,2nd identity [8,9]. Furthermore, cacti are prominent elements of Mexico's national symbols, reflected in the central motif of the national flag, in which Opuntia figures as an emblem of territorial and civilizational identity.

Despite this ecological and cultural relevance, Cactaceae represent one of the most threatened plant families globally. According to the most comprehensive global assessment conducted to date, approximately 31% of cactus species are threatened with extinction, driven primarily by illegal collection, habitat loss due to agricultural expansion and urban development, and climate change [2]. In Mexico, both the national legislation, particularly the Official Mexican Law (NOM-059-SEMARNAT-2010) [10], and international frameworks, notably the International Union for Conservation of Nature (IUCN) [11], anD the Red List and the Convention on International Trade in Endangered Species of Wild Fauna and Flora (CITES, Appendix I and II) [12], establish legal and normative instruments for the protection and regulation of species in this family. These instruments categorize species according to extinction risk criteria, providing a critical baseline for conservation planning at both national and global levels.

In this context, botanical gardens have historically played a central role in the ex situ conservation of plant biodiversity, particularly for threatened and endemic species. The first botanical gardens in Mexico emerged during the colonial period, with the Royal Botanical Garden of New Spain established in 1788 by decree of Viceroy Juan Vicente de Güemes, constituting one of the earliest formal institutions for scientific botanical study in the Americas [13]. Since the twentieth century, botanical gardens in Mexico have evolved considerably in their conservation mandates, transitioning from ornamental and didactic spaces toward active repositories of living collections with strategic conservation value [14,15,16]. Institutions such as the Jardín Botánico del Instituto de Biología of the Universidad Nacional Autónoma de México (UNAM) and many other Mexican botanical gardens have become internationally recognized models of integration between plant conservation, scientific research, and public education [18,19].

The Botanical Garden of the Facultad de Estudios Superiores Cuautitlán, UNAM, hereafter FESC Botanical Garden, is in the municipality of Cuautitlán Izcalli, State of Mexico, within a predominantly urbanized and industrialized landscape in the northern metropolitan area of Mexico City [19]. As a living collection embedded in an environment characterized by heavy anthropogenic pressure, this garden performs critical functions that extend beyond academic and didactic goals, serving as a refuge for plant species that are increasingly displaced from their natural habitats due to land-use change. Despite its strategic position and institutional affiliation, the cactus collection at FES Cuautitlán has not been subjected to a systematic taxonomic inventory or a formal evaluation of the conservation status of its accessions under current national and international normative frameworks.

As part of the requirements for membership in the Mexican Association of Botanical Gardens, institutions are expected to maintain up-to-date inventories of their living collections, among other obligations. This also includes ensuring the proper preservation, documentation, and ongoing maintenance of these collections in accordance with recognized botanical garden standards [16], therefore, the present study aims to provide a complete taxonomic inventory of the cactarium held at the FESC Botanical Garden, UNAM, and to evaluate the conservation status of each registered species according to the criteria established by NOM-059-SEMARNAT-2019, the IUCN Red List, and CITES appendices.

2. Materials and Methods

The Cactarium of the FESC Botanic Garden houses a diverse collection of cacti along with other plant species. Specimens are maintained both inside a main greenhouse and in outdoor exhibition areas accessible to visitors (Figure 1). Plants displayed outdoors are established directly in the ground and arranged in landscaped groupings designed for educational, conservation, and outreach purposes. Research and conservation activities are primarily conducted using specimens cultivated in pots [16]. Between January 2024 and June 2025, a comprehensive inventory of the living collection was carried out, and all specimens were documented in a digital database. Cacti represented the most abundant plant group within the collection, and their taxonomic identification was verified by one of collection curators (Alejandro de la Rosa-Tilapa) and by a taxonomist specialized in this family (Gabriel Olalde). The conservation status was revised in NOM-059-SEMARNAT-2010 [10], the IUCN Red List [11], and CITES appendices [12], the origin status was registered according to specialized literature [20]. The full taxonomic names were obtained from International Plant Name Index [21].

3. Results

The cactarium of the FES-Cuautitlan Botanical garden encompassed 62 genera and 342 taxa, including 26 subspecies or varieties (Table 1, Figure 2, Figure 3 and Figure 4). Of the 342 taxa, 259 are native of which 215 are endemic to Mexico, and 83 exotic species.

The conservation assessment indicates that 180 taxa are classified as Least Concern (LC), representing the largest proportion of the collection. However, the collection also includes 45 Vulnerable (VU) taxa, 41 Endangered (EN) taxa, and 20 Critically Endangered (CR) taxa, demonstrating that a substantial number of species are considered at risk of extinction. Additionally, 4 taxa are classified as Near Threatened (NT), 6 as Data Deficient (DD), and 46 have not yet been evaluated (NE) under the IUCN Red List criteria.

According to the Mexican conservation standard (NOM-059-SEMARNAT), 65 taxa are listed as Extinction Risk (P) and 47 are classified as Subject to Special Protection (Pr). The remaining 230 taxa are not currently included (NE) in the national risk categories. These figures indicate that the collection contains an important representation of taxa recognized as conservation priorities at both national and international levels.

4. Discussion

The present study documents a comprehensive ex situ collection comprising 341 cactus species, including native, endemic, and exotic taxa whose conservation status was assessed using three complementary frameworks: the International Union for Conservation of Nature (IUCN) Red List, NOM-059-SEMARNAT, and the Convention on International Trade in Endangered Species of Wild Fauna and Flora (CITES). Collectively, these data reveal a collection with considerable conservation value, characterized by a high representation of Mexican endemic species and a large proportion of taxa protected under national and international legislation. This combination highlights the collection not only as a repository of taxonomic diversity but also as a valuable resource for biodiversity conservation, scientific research, and environmental education.

A prominent feature of the cactarium at FESC Botanical Garden is the predominance of endemic species, a pattern that reflects Mexico as the world principal center of cactus diversity and endemism [1,2]. Nearly half of all described cactus species occur within the country, and a substantial proportion of them are found nowhere else [22,23]. Previous studies have attributed this exceptional diversity to the interaction of complex geological history of Mexican territory, marked environmental heterogeneity, pronounced climatic gradients, and the extensive development of arid and semi-arid ecosystems [24]. Together, these factors have promoted repeated episodes of geographic isolation and ecological specialization, creating ideal conditions for diversification within the family Cactaceae.

The high proportion of endemic taxa considerably enhances the conservation significance of the collection. Unlike species with broad geographic distributions, many Mexican cacti are microendemic, occupying extremely restricted habitats that may be confined to a single limestone outcrop, gypsum deposit, volcanic hillside, or isolated valley [2,25]. As a consequence, even localized disturbances can threaten the persistence of entire global populations, the habitat degradation [2,25associated with land-use change, mining, infrastructure development, or illegal plant extraction may therefore have irreversible consequences for these narrowly distributed species [2,22,26,27]. In this context, ex situ collections become an essential complement to in situ conservation by preserving genetic resources that might otherwise be lost in the wild [28].

Evaluation of the conservation status of the recorded taxa further emphasizes the biological importance of this collection. A substantial proportion of the species are classified within one or more threatened categories of the IUCN Red List, including Critically Endangered (CR), Endangered (EN), and Vulnerable (VU), whereas comparatively fewer taxa are categorized as Least Concern (LC) or Near Threatened (NT). This distribution indicates that threatened species constitute a significant component of the collection rather than isolated exceptions, underscoring its relevance for conservation-oriented research and management. These findings closely agree with the global assessment in which were the Cactaceae is recognized as one of the most threatened families of vascular plants worldwide, with nearly one-third of all known species facing an elevated risk of extinction [2]. Accordingly, the large number of threatened taxa documented in the present inventory should not be interpreted as an isolated characteristic of this collection but rather as a reflection of the broader conservation crisis affecting cactus diversity in Mexico.

Many species recognized as threatened by the IUCN are also protected under NOM-059-SEMARNAT and regulated through CITES Appendices I or II, demonstrating a high degree of agreement among international and national conservation policies. This consistency reinforces confidence in the conservation status importance assigned to these taxa and highlights the value of integrating multiple assessment systems when establishing conservation priorities.

Nevertheless, some discrepancies among these frameworks are also evident. Several taxa remain classified as Not Evaluated (NE) by the IUCN despite receiving legal protection under Mexican legislation or being included within the CITES appendices. Conversely, certain species recognized internationally as threatened are not assigned equivalent protection categories under national regulations. For example, Astrophytum myriostigma and Astrophytum ornatum are classified as Least Concern (LC) by the IUCN but remain protected under NOM-059 (Pr), reflecting a more precautionary national approach. Similarly, Echinocactus horizonthalonius and Echinocactus platyacanthus are also listed as LC by the IUCN while receiving legal protection in Mexico (Pr). In contrast, Coryphantha clavata, Coryphantha cornifera, and Coryphantha pycnacantha are included in CITES Appendix II but lack protection under NOM-059 despite their international regulation. Conversely, species such as Disocactus flagelliformis, Disocactus phyllanthoides, and Coryphantha pulleineana remain Not Evaluated (NE) by the IUCN and are likewise absent from NOM-059, although they are regulated through CITES Appendix II. These discrepancies illustrate that the three conservation instruments differ in their evaluation criteria, update frequency, and conservation objectives, highlighting the importance of integrating international assessments with national legislation to provide a more comprehensive framework for cactus conservation in Mexico.

The inclusion of most species in Appendix I reflects one of the principal threats currently facing Mexican cacti: illegal collection for ornamental purposes. Unlike many other threatened plant groups that are primarily affected by logging or agricultural expansion, numerous cactus species are removed directly from natural populations to satisfy commercial demand among collectors. Rare species with unusual morphologies, limited geographic ranges, and slow growth rates command particularly high market values, resulting in continued harvesting pressure despite existing legal protections [27]. The conservation value of the collection extends well beyond its taxonomic richness. By safeguarding a substantial number of endemic and threatened species that are recognized under multiple conservation frameworks, the collection constitutes an important genetic reservoir capable of supporting future research, conservation programs, propagation initiatives, and long-term efforts aimed at preserving one of the most distinctive components of Mexican botanical heritage.

The taxonomic composition of the collection further highlights its scientific and conservation value by encompassing a broad representation of evolutionary lineages within the family Cactaceae, genera such as Mammillaria Haw., Turbinicarpus (Backeb.) Buxb. & Backeb., Echinocereus Engelm., Ferocactus Britton & Rose, Thelocactus (K.Schum.) Britton & Rose, Opuntia Mill., and Coryphantha (Engelm.) Lem. are particularly well represented, reflecting much of the morphological, ecological, and evolutionary diversity that characterizes Mexican cacti. The inclusion of species with contrasting growth forms, reproductive strategies, habitat preferences, and pollination syndromes makes this collection especially valuable for studies addressing taxonomy, ecology, evolutionary biology, and conservation.

Among the most remarkable groups represented is the genus Ariocarpus Scheidw., widely recognized as one of the most distinctive evolutionary lineages within the Cactaceae [4,5]. Species such as Ariocarpus bravoanus, Ariocarpus agavoides, and Ariocarpus scapharostrus are classified as Endangered or Critically Endangered and are simultaneously protected under CITES Appendix I and Mexican environmental legislation. Their distributions are exceptionally restricted, with most populations occurring on isolated limestone outcrops within the Chihuahuan Desert. Their characteristic morphology, consisting of flattened stems that remain partially buried in the substrate, is an adaptation to extremely arid environments but also complicates field detection and demographic monitoring [29]. Among these taxa, Ariocarpus bravoanus deserves particular attention because it is considered one of the rarest cactus species worldwide, for which natural populations are confined to a very small area in San Luis Potosí, where individuals occur at extremely low densities [22,30,31,32]. Habitat fragmentation, illegal collection, and limited natural recruitment have contributed to a continuous decline in population size [32]. Furthermore, the species is characterized by slow growth, delayed reproductive maturity, and narrow ecological requirements, factors that greatly reduce its capacity to recover after disturbance [30,31]. Under these circumstances, maintaining genetically representative ex situ populations becomes a fundamental component of long-term conservation strategies.

Another species of exceptional conservation interest is Geohintonia mexicana, a monotypic genus endemic to gypsum cliffs in Nuevo León [22,33]. Owing to its highly restricted distribution and unique evolutionary history, the species is classified as Endangered by the IUCN and receives the highest level of protection under both NOM-059-SEMARNAT and CITES Appendix I. Unlike species-rich genera, the extinction of Geohintonia Glass & W.A.Fitz Maur., would represent the loss of an entire evolutionary lineage, highlighting the importance of conserving phylogenetically unique taxa in addition to preserving species richness.

A comparable situation is observed for Obregonia denegrii, another monotypic genus endemic to northeastern Mexico [34]. The distinctive geometric arrangement of its tubercles has made this species particularly attractive to collectors, resulting in decades of harvesting pressure despite international trade regulations. Although natural populations remain highly vulnerable, the cultivation of Obregonia Fric in botanical collections offers opportunities for research, propagation, and environmental education while potentially reducing demand for wild-collected specimens [35].

The collection also contains an exceptional representation of the genus Turbinicarpus, one of the most diverse groups of narrowly distributed cacti in Mexico [22,36]. More than twenty species are included in the FESC cactarium, the majority of which are categorized as Vulnerable, Endangered, or Critically Endangered and protected under CITES Appendix I. This concentration of threatened taxa underscores both the conservation significance of the collection and the extraordinary diversity of this genus within the Chihuahuan Desert. Species such as Turbinicarpus alonsoi, Turbinicarpus dickisoniae, Turbinicarpus jauernigii, Turbinicarpus laui, and Turbinicarpus zaragozae exemplify the conservation challenges associated with extreme microendemism. Many are restricted to single hillsides, isolated valleys, or small geological formations covering only a few hectares [25], and also make these species exceptionally vulnerable because localized disturbances, including mining, road construction, livestock grazing, or illegal plant collection, can rapidly affect a substantial proportion of the populations.

The genus Mammillaria constitutes the largest taxonomic group represented in the collection and illustrates particularly well the contrasting conservation scenarios observed within Mexican cacti. Although several species remain relatively widespread and are currently classified as Least Concern, the inventory also includes a remarkable number of taxa facing a high risk of extinction. Species such as Mammillaria pectinifera, Mammillaria herrerae, Mammillaria luethyi, Mammillaria moelleriana, Mammillaria oteroi, Mammillaria perezdelarosae, Mammillaria sanchez-mejoradae, Mammillaria solisioides, and Mammillaria theresae are all recognized within the highest threat categories because of their restricted distributions, small population sizes, and highly specialized habitat requirements [25]. The conservation problems affecting these species are remarkably similar. Most occur in isolated populations associated with specific geological substrates and exhibit slow growth, limited recruitment, and low dispersal capacity. Their small size and ornamental value have further increased their susceptibility to illegal collection, making them among the most sought-after Mexican succulents in international horticultural markets. The species Mammillaria pectinifera illustrates many of these challenges. Endemic to limestone outcrops within the Tehuacán-Cuicatlán Valley, one of the most important centers of plant diversity in Mexico, this species has experienced substantial population declines despite occurring within protected areas. Habitat fragmentation and historical overcollection have reduced the abundance of mature individuals [37,38], and similar demographic trends have been documented for M. herrerae and M. luethyi, both of which remain confined to extremely small geographic ranges [39,40].

Another important species included in Cactarium at FESC botanical garden is Strombocactus disciformis. It is the sole representative of the genus Strombocactus Britton & Rose and is naturally restricted to limestone outcrops in the states of Hidalgo, Queretaro, and San Luis Potosi, where it inhabits steep rocky slopes under highly specialized ecological conditions [25]. The species exhibits extremely slow growth and low recruitment rates, making natural populations particularly vulnerable to disturbance [41]. Although its small size makes it inconspicuous in the field, S. disciformis has long been targeted by illegal collectors because of its unique morphology and high ornamental value in the international succulent trade [42].

Likewise, Ortegocactus macdougallii, a monotypic genus endemic to Oaxaca, represents another example of a species whose conservation importance extends beyond its rarity [43]. Because the extinction of monotypic genera would eliminate entire evolutionary lineages, preserving these taxa contributes disproportionately to maintaining the evolutionary history and genetic diversity [44].

Collectively, these examples demonstrate that the conservation significance of the collection is determined not only by the number of threatened species it contains but also by the exceptional evolutionary, ecological, and biogeographic uniqueness of many of its representatives. By safeguarding multiple microendemic taxa, several monotypic genera, and numerous species protected under international legislation, the collection represents an invaluable resource for future research and for the long-term conservation of one of the richest centers of cactus diversity on Earth.

In addition to the numerous threatened microendemic taxa, the collection includes several cactus species that are widely regarded as symbols of Mexican natural and cultural heritage. These species not only possess considerable ecological value but have also played an important role in the history of Mexico, traditional knowledge, and sustainable use of arid ecosystems. Their inclusion considerably broadens the significance of the collection by preserving taxa that represent both biological diversity and cultural identity.

One of the most recognizable species is Cephalocereus senilis, commonly known as the Old Man Cactus. Endemic to central Mexico, this species is distinguished by its dense covering of long white hairs, an adaptation that reflects sunlight, reduces stem temperature, and minimizes water loss under intense desert conditions [45]. Its striking appearance has made it one of the best-known ornamental cacti worldwide and an important ambassador for desert plant conservation. Despite its popularity in cultivation, wild populations remain fragmented and continue to experience habitat degradation, emphasizing the importance of maintaining genetically diverse ex situ collections. The collection includes Lophophora williamsii, a species of exceptional ethnobotanical importance. For centuries, this cactus has held profound ceremonial and spiritual significance for several Indigenous peoples of northern Mexico, where it continues to play a central role in traditional cultural practices and ceremonial significance for several Indigenous peoples of northern Mexico and the southern United States, particularly the Wixárika (Huichol), Rarámuri (Tarahumara) and Cora (Náayeri) [46]. For centuries, peyote has been regarded as a sacred plant that facilitates communication with the spiritual world, promotes healing, and reinforces cultural identity through ritual practices passed down across generations [47]. Nevertheless, increasing harvesting pressure, habitat transformation, and legal restrictions associated with its psychoactive properties have generated growing concern regarding the long-term viability of natural populations [48,49] (Terry et al., 2011; 2012). Its close relative, Lophophora diffusa, illustrates an even more critical conservation scenario. Unlike L. williamsii, this species is restricted to a relatively small region of Querétaro, where habitat loss associated with quarrying activities, agricultural expansion, and urban development has substantially reduced the availability of suitable habitat [50]. Its narrow distribution and limited population size make the species particularly vulnerable to additional environmental disturbances.

From an evolutionary perspective, the collection encompasses an extraordinary diversity of growth forms and adaptive strategies. Massive columnar species coexist with miniature globose cacti, epiphytic taxa, shrubby forms, and highly specialized rock-dwelling species, illustrating the remarkable adaptive radiation that has occurred within the family Cactaceae. This diversity reflects millions of years of evolution under contrasting environmental conditions and provides exceptional opportunities for comparative studies addressing adaptation, diversification, and ecological specialization. The value of the collection extends far beyond its impressive taxonomic richness. It preserves species that are ecologically indispensable, evolutionary unique, culturally significant, and economically valuable. Consequently, the collection should be viewed not only as an ex situ conservation resource but also as an important platform for ecological research, public education, sustainable propagation, and the long-term preservation of Mexico's exceptional cactus diversity.

Another important consideration is that conservation categories represent a snapshot of current knowledge rather than permanent classifications. Taxonomic revisions, newly discovered populations, updated demographic information, and changes in habitat conditions may substantially modify conservation assessments over time. Several species included in the collection remain categorized as Not Evaluated (NE) or Data Deficient (DD), indicating that available ecological or demographic information remains insufficient for a comprehensive extinction risk assessment. These categories therefore represent significant knowledge gaps rather than evidence of low conservation concern.

5. Conclusions

Overall, the present inventory demonstrates that the evaluated collection represents a highly valuable ex situ repository of Mexican cactus diversity. The presence of 341 species, including numerous endemic taxa, microendemics, monotypic genera, and species classified under national and international conservation frameworks, highlights its exceptional scientific and conservation significance. The collection preserves not only taxonomic richness but also a substantial proportion of the evolutionary history, ecological diversity, and genetic resources that characterize one of the world's most distinctive plant families.

The results further emphasize that the conservation of Mexican cacti extends beyond preventing individual species extinctions. Protecting these plants also safeguards complex ecological interactions, unique evolutionary lineages, cultural traditions, and ecosystem services that sustain biodiversity within arid environments. As anthropogenic pressures continue to intensify through habitat transformation, illegal collection, and climate change, well-managed ex situ collections will become increasingly important components of integrated conservation strategies. Ultimately, the long-term persistence of Mexican Cactaceae will depend upon combining scientifically managed ex situ conservation, effective protection of natural habitats, continuous ecological and genetic research, strong legal frameworks, and active participation of society. The collection documented in this study represents an important contribution toward these objectives and provides a valuable platform for future research, education, restoration, and biodiversity conservation at both national and international scales.