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Cycas

Cycas is the type genus and largest genus within the family Cycadaceae, comprising approximately 117 accepted species of ancient, dioecious gymnosperms that exhibit a palm-like growth habit despite their closer evolutionary relation to conifers than to true palms.^[1] These plants originated in the pre-mid-Permian period and represent one of the earliest lineages of seed plants, having survived major geological and climatic changes, including a significant decline associated with the rise of flowering plants in the Cretaceous, with extant lineages diversifying around 12 million years ago.^[2] Characterized by stout, unbranched trunks that can reach up to 40 feet (12 meters) in height and crowns of large, pinnate, fern-like fronds emerging in whorls, Cycas species are evergreen perennials adapted to a variety of habitats including rocky slopes, grasslands, forests, and swampy areas.^[3] Native primarily to tropical and subtropical regions of the Old World—from eastern Africa (Kenya to Mozambique) through southern Asia, India, Australia, and the western Pacific islands—the genus shows high diversity in areas like southwestern China, where 23 species occur across four taxonomic sections.^[1]^[2] Cycas plants are dioecious, with male individuals producing conspicuous pollen cones and females bearing clusters of seed-bearing megastrobili that develop into bright orange or red seeds; reproduction relies on insect or wind pollination, and they thrive in well-drained, fertile to saline soils under full sun to partial shade conditions.^[3] Many species demonstrate notable genetic diversity at the population level, with average expected heterozygosity around 0.44 and strong differentiation between populations (F_ST ≈ 0.20), reflecting adaptation to fragmented habitats.^[2] Widely cultivated as slow-growing ornamentals in warmer climates (USDA zones 9a–11b) and as houseplants, species like C. revoluta (sago palm) are prized for their glossy, arching fronds and drought tolerance, though they require careful management to prevent overwatering.^[3] However, all parts of Cycas plants are highly toxic due to the presence of cycasin, a compound causing severe gastrointestinal distress, seizures, and liver failure in humans, pets, and livestock, with seeds containing the highest concentrations.^[3] Conservation concerns are acute, as approximately 71% of cycad species, including most Cycas, are threatened globally per IUCN assessments as of 2025, driven by habitat loss, overcollection, and invasive species; in China alone, 65% qualify as Plant Species with Extremely Small Populations, prompting in situ protections in nature reserves and ex situ efforts in botanical gardens.^[4]^[2]

Description

Morphology

Cycas species exhibit a distinctive palm-like habit, characterized by an unbranched, cylindrical trunk that serves as the primary structural support. This trunk, often referred to as the caudex, can attain heights of up to 10-15 meters in certain species, such as Cycas pectinata, with a diameter typically ranging from 20 to 50 cm. The upper portion of the trunk bears a dense crown of 50-150 evergreen, pinnate leaves, which can extend up to 3 meters in length, creating a symmetrical rosette appearance. These plants are dioecious, with male and female reproductive structures occurring on separate individuals.^[5] The leaves of Cycas are large, compound structures with a central rachis bearing 100-300 linear to lanceolate leaflets arranged pinnately on either side. Each leaflet is typically 10-30 cm long, with a prominent midvein and revolute margins that often feature sharp spines, particularly evident in species like Cycas revoluta, which enhances protection against herbivores. Young leaves emerge in a circinate fashion, uncoiling gradually, and are covered in a fine layer of brown tomentum that persists on the petiole and rachis. The petiole itself is stout, up to 1 meter long, and armed with paired spines along its edges in many taxa.^[6]^[7] Reproductive morphology in Cycas is prominent and sexually dimorphic. Male plants produce robust, ovoid cones at the apex, displacing the leaf crown temporarily; these cones can measure up to 80 cm in length and 40 cm in diameter, consisting of numerous spirally arranged microsporophylls that release pollen. In contrast, female plants develop loose clusters of 20-50 megasporophylls, which are leaf-like, flattened structures 20-40 cm long, each bearing 2-6 ovules along the margins that develop into large, orange to red seeds upon maturation, up to 6 cm in diameter with a fleshy outer layer.^[8]^[9] Growth form in Cycas varies with age and species, with the caudex frequently remaining subterranean or partially buried in young plants, giving the appearance of a low rosette before gradually elevating above ground over decades. Leaves are initiated spirally at the stem apex but persist to form a dense, apparently whorled crown due to their longevity and upright orientation. This slow-growing architecture contributes to the plant's resilience in arid environments, though offsets occasionally form at the base for vegetative propagation in some taxa.^[10]

Anatomy

The root system of Cycas features specialized coralloid roots that are dichotomously branched, apogeotropic structures often clustered near the soil surface to facilitate nutrient uptake in nutrient-poor environments.^[11] These roots form symbiotic associations with nitrogen-fixing cyanobacteria, primarily Nostoc species, which colonize the cortical cells and enable biological nitrogen fixation, enhancing the plant's adaptation to low-nitrogen soils.^[12] Internally, coralloid roots exhibit a single-layered epidermis, a broad cortex with mucilage canals and algal zones, and a central stele containing vascular tissues, supporting both structural integrity and symbiotic exchange.^[13] Vascular tissues in Cycas undergo gymnospermous secondary growth, producing extensive secondary xylem and phloem through the activity of a vascular cambium, which allows for substantial stem thickening and long-term structural support. The xylem consists primarily of tracheids with bordered pits, providing water conduction, while the phloem includes sieve cells and albuminous cells for nutrient transport.^[14] Resin canals, lined by epithelial cells, are distributed throughout the cortex, pith, and occasionally the secondary wood, secreting resinous substances that serve as a chemical defense against pathogens and herbivores. Leaf anatomy in Cycas is adapted for water conservation and mechanical strength, featuring a thick cuticle on epidermal cells that minimizes transpiration in arid habitats.^[15] Stomata are sunken, haplocheilic types restricted to the abaxial surface, with overarching subsidiary cells that further reduce water loss. Sclerenchyma fibers surround the vascular bundles in leaflets, providing rigidity to the pinnate structure, while the midribs contain diploxylic vascular bundles with centripetal and centrifugal xylem, complemented by parallel veins for efficient transport.^[16] Reproductive anatomy in Cycas includes pollen grains that germinate to form pollen tubes lacking siphonogamy, meaning the tubes do not directly deliver sperm to the egg but release them into the nucellar fluid for swimming.^[17] The male gametes are multiflagellated sperm cells, each bearing approximately 40,000 flagella arranged in 5–10 sinistral spirals, representing the largest and most flagella-rich sperm in the plant kingdom and enabling motility toward the archegonium.^[17] These sperm develop within the pollen tube over several months, highlighting the prolonged gametophytic phase characteristic of cycads.^[18]

Taxonomy and phylogeny

Etymology and classification history

The genus name Cycas originates from the Greek term koikas, referring to a type of palm tree, which highlights the superficial resemblance of cycads to palms; Linnaeus adopted a manuscript variant or misspelling as kykas in his original publication.^[19]^[20]^[21] Cycas was established by Carl Linnaeus in Species Plantarum (1753), with C. circinalis designated as the type species based on descriptions and illustrations of specimens from the Malabar Coast of southern India.^[22]^[23] Early European botanists frequently misidentified cycads as palms or related gymnosperms due to their pinnate leaves and arborescent habit.^[22] The type species C. circinalis L. was later lectotypified by Rudolph Florin in 1956 to resolve ambiguities in its application, as historical descriptions encompassed multiple taxa now recognized as distinct species.^[24] In the 19th century, taxonomic progress accelerated with Augustin Pyramus de Candolle's comprehensive synthesis in Prodromus Systematis Naturalis Regni Vegetabilis (1868), which cataloged known Cycas species and emphasized morphological variation without formal sectional divisions.^[25]^[26] The first explicit infrageneric classification emerged in Julius Schuster's 1932 monograph, where he divided the genus into three sections primarily based on leaflet shape, venation, and reproductive structures, recognizing eight species with numerous subspecies and varieties.^[26]^[27] Subsequent revisions in the late 20th century refined these groupings, leading to the modern recognition of 117 species as of 2025.^[28]^[1]^[29]

Species diversity and sections

The genus Cycas comprises 117 accepted species, all placed within the family Cycadaceae, making it the sole genus in this family.^[1] Taxonomists recognize six major sections within Cycas, primarily delimited by reproductive morphology such as megasporophyll structure and leaflet characteristics. Section Cycas includes Old World species with simple, unbranched megasporophylls lacking apical spines. Section Indosinenses encompasses over 40 species from Indochina, often featuring pinnate leaves with softly serrulate leaflet margins. Section Stangerioides is characterized by Australian taxa with compound leaflets and more robust megasporophylls. The remaining sections—Asiorientales, Panzhihuaenses, and Wadeae—further differentiate based on regional distributions and subtle variations in cone structure and seed morphology.^[30]^[31] Species diversity is concentrated in several hotspots, with 34 species native to Australia, 27 in Vietnam, and 23 in China.^[1] Representative examples include Cycas revoluta, endemic to Japan and noted for its stiff, revolute leaflets, and Cycas thouarsii from Madagascar, distinguished by its large, globose seeds.^[32]^[33]^[34]^[1]^[35] Infrageneric delimitation relies on morphological traits, including leaflet shape (entire to deeply dissected), presence or absence of marginal spines, and megasporophyll form (from elongate and spinescent to flattened and spineless). These features, combined with habitat-specific adaptations, facilitate species identification amid the genus's overall uniformity in habit.^[35]^[31]

Phylogenetic relationships

Cycas represents the basal genus within the order Cycadales, positioned as sister to all other cycad families, including Zamiaceae and Stangeriaceae, based on analyses of chloroplast and nuclear DNA sequences.^[36] This divergence is estimated to have occurred approximately 300 million years ago during the mid-Permian, marking the early radiation of extant cycad lineages.^[30] Within the broader gymnosperm phylogeny, cycads form a monophyletic group that, together with Ginkgo, is sister to the remaining living gymnosperms (conifers and gnetophytes), as supported by nuclear and plastid phylogenomic data.^[37] Phylogenetic analyses of Cycas reveal three main infrageneric clades corresponding to geographic regions: Indochinese, Australasian, and African, corroborated by plastid markers such as matK and nuclear loci including ITS.^[31] These clades reflect the genus's pantropical distribution and evolutionary history of vicariance and dispersal. However, some morphologically defined sections exhibit polyphyly; for instance, section Punctata shows non-monophyletic groupings in molecular trees, indicating convergence in traits like leaflet punctations.^[31] The African clade, comprising species like C. thouarsii from Madagascar, diverges early and highlights long-distance dispersal events across the Indian Ocean. A landmark 2018 multi-locus study, utilizing four chloroplast intergenic spacers and seven low-copy nuclear genes across over 90% of the 117 recognized Cycas species, provided the most comprehensive resolution of genus-level relationships to date.^[31] This phylogeny identified 13 well-supported clades aligning broadly with six recognized sections (Asiorientales, Indosinenses, Wadeae, Cycas, Panzhihuaenses, and Stangerioides), though with evidence of non-monophyly in Stangerioides and Indosinenses. Taxonomic implications include recommendations to elevate certain subsections to full sectional status to better reflect genetic divergence, such as recognizing monophyletic groups within the polyphyletic Indosinenses. Cycas shares key reproductive traits with Ginkgo biloba, notably multiflagellated sperm that enable swimming in pollen tubes, a primitive feature distinguishing both from pollen-tube conifers; this similarity underscores their close phylogenetic affinity as the sister clade to other gymnosperms.^[37] Unlike conifers, which produce non-motile pollen, this shared trait in Cycas and Ginkgo reflects retention of ancestral gymnosperm characteristics from their common ancestor around 300 million years ago.^[37]

Distribution and ecology

Geographic range

The genus Cycas is distributed across the tropical and subtropical regions of the Old World, ranging from eastern Africa through southern Asia to Australia and the western Pacific islands, with no native species in the Americas. This distribution spans latitudes approximately from 27°S to 18°N, encompassing diverse archipelagos and continental margins. The African representative is C. thouarsii, which occurs in coastal forests from eastern Africa (Kenya to Mozambique) and on Indian Ocean islands including Madagascar.^[2]^[38]^[39] Centers of diversity for Cycas are concentrated in Indochina, Australia, and Indonesia. In Indochina, Vietnam hosts around 27 species and China approximately 23, many concentrated in southwestern mountainous areas and river drainages like the Red River. Australia supports about 34 species, predominantly in northern and eastern regions such as Queensland and the Northern Territory. Indonesia has 10 species across its islands, including endemics on Java, Sulawesi, and Flores. Other notable areas include India (14 species) and Pacific islands like New Caledonia.^[2]^[40]^[38] Disjunct distribution patterns characterize the genus, with the isolated Madagascan outlier representing a long-distance dispersal event, likely recent based on molecular evidence. In contrast, the Australian radiation reflects post-Gondwana breakup diversification, where Cycas lineages expanded across the continent following the Jurassic-Cretaceous fragmentation of the supercontinent.^[41]^[42] Endemism in Cycas is exceptionally high, with most species restricted to a single country, underscoring their narrow ranges and vulnerability. For instance, C. megacarpa is confined to central Queensland woodlands in Australia. This pattern of localized endemism is evident across regions, with nearly all species in Australia, China, Vietnam, and Indonesia being country-endemic.^[38]

Habitat preferences

Cycas species predominantly inhabit tropical and subtropical regions, thriving in seasonal dry forests, savannas, and monsoon forests where they often occupy understory positions.^[43] These environments feature hot, humid conditions with distinct wet and dry seasons, including mean diurnal temperature ranges of 11–12°C and low precipitation in the driest months (5–7 mm), as observed in suitable habitats along dry-hot river valleys.^[44] They favor well-drained, infertile sandy or rocky soils, including limestone, shale, and sandstone slopes with elevated exchangeable calcium levels (7–19 me/100 g), typically at low to mid-elevations (100–1673 m).^[44]^[2] Ecologically, Cycas plants engage in symbiotic relationships that enhance their persistence in nutrient-poor settings. Their coralloid roots host nitrogen-fixing cyanobacteria, such as Anabaena, enabling atmospheric nitrogen fixation and reducing reliance on soil nutrients.^[43]^[45] Additionally, arbuscular mycorrhizal fungi colonize their roots, facilitating phosphorus uptake in infertile substrates and contributing to ecosystem nutrient cycling.^[46] These interactions position Cycas as understory components in sparse woodlands, grasslands, and evergreen broadleaf forests, where they share resources like nitrogen and carbon through soil networks, fostering habitable conditions for associated organisms.^[47]^[2] Adaptations to environmental stresses underscore their resilience in variable habitats. Cycas exhibits drought tolerance, surviving arid conditions with annual precipitation as low as 300 mm through efficient water conservation and slow growth rates.^[48] Fire tolerance is notable, with adult plants resisting low-severity burns and resprouting new leaves and cones from protected buds post-fire, a trait stimulated by nutrient release from ash.^[49]^[48] Habitat specificity varies; for instance, species like Cycas hoabinhensis occur in limestone karst landscapes of northern Vietnam, while Cycas armstrongii persists in sandy savannas and coastal areas of northern Australia.^[50]^[51] In biodiversity contexts, Cycas serves a keystone role by supporting specialized insect communities, including beetles that feed on leaves and pollinate cones, thereby influencing trophic dynamics in their habitats.^[52] These plants produce defensive toxins like cycasin, which deter generalist herbivores while sustaining adapted insect populations, indirectly shaping community structure through chemical mediation.^[53]

Reproduction

Sexual reproduction

Cycas species are strictly dioecious, with reproductive structures developing on separate male and female plants.^[54] Male plants produce compact cones consisting of numerous microsporophylls, each bearing microsporangia that release pollen, while female plants bear loose clusters of megasporophylls, each with two to nine ovules but lacking a true cone structure.^[55] Cone maturation follows a seasonal phenology, typically occurring during the dry season in native habitats; for instance, in Australian species like Cycas media, male cones emerge and release pollen from May to August, with pollen shedding lasting 2–4 weeks per cone.^[56] Pollination in Cycas is primarily entomophilous, mediated by specialized insects such as beetles that breed within male cones and carry pollen to female ovules via pollination drops rich in sugars and proteins, although anemophily via lightweight, non-saccate pollen grains dispersed by wind also occurs in some species.^[57]^[58] In entomophilous cases, such as Cycas media and Cycas revoluta, pollen is transferred by beetles, particularly weevils (Curculionidae) that breed within male cones and carry pollen to female ovules via pollination drops rich in sugars and proteins.^[59] These drops, secreted by the micropyle, capture pollen and retract to draw it into the nucellus, with fertilization delayed by several months—often 3–7—allowing pollen tube growth and gametophyte development.^[60] Fertilization in Cycas involves siphonogamy followed by zoogamy, where multiflagellate sperm cells—among the largest in plants, up to 300 μm long with thousands of flagella arranged in coils—swim through the pollen tube fluid to reach the archegonia within the female gametophyte.^[55] Unlike angiosperms, double fertilization is absent; a single motile sperm fuses with the egg to form a zygote, which develops into an embryo supported by a suspensor, while the second sperm degenerates.^[54] The archegonia, numbering 2–6 per ovule, are embedded in the nucellus, and successful fertilization yields a single embryo per seed.^[55] Seed development proceeds slowly post-fertilization, with the ovule's integument differentiating into three layers: an outer fleshy sarcotesta, often bright red and attractive to dispersers; a stony sclerotesta for protection; and an inner endotesta.^[55] The sarcotesta aids animal-mediated dispersal by birds or mammals in many species, while the embryo matures over 6–12 months, regulated by genes such as LAFL transcription factors and phytohormones like gibberellin.^[54] Germination is hypogeal, with the cotyledons remaining belowground, and typically requires 3–9 months under suitable moist, warm conditions (25–30°C), though viability can persist if seeds are stored dry at low temperatures.^[61]

Asexual propagation

In addition to sexual reproduction, Cycas species can reproduce asexually through vegetative means. Vegetative reproduction in Cycas typically arises from mature plants via basal offsets or suckers emerging from the caudex, which can be naturally detached to form independent individuals. Adventitious bulbils, or cresting buds, also develop in the axils of scale leaves on the stem, serving as propagules that grow into new plants upon separation. Branching is infrequent in Cycas but may occur adventitiously in response to injury or damage, leading to multiple stems from a single caudex.^[62]^[63] Artificial asexual propagation builds on these natural processes to support conservation and cultivation. Offsets are divided from the parent plant and rooted in suitable media, often achieving high establishment rates due to their pre-formed vascular connections. Micropropagation via tissue culture, utilizing shoot tips or zygotic embryos as explants, enables seedless clonal production; protocols for species like Cycas revoluta have reported germination rates up to 73% and plantlet regeneration with over 90% survival post-acclimatization in optimized conditions. These techniques maintain genetic fidelity, proving essential for propagating endangered taxa such as Cycas beddomei in ex situ conservation programs.^[64]^[65]^[66]

Evolution

Fossil record

The fossil record of Cycas and its ancestors within the Cycadales extends back to the late Paleozoic, with the earliest evidence consisting of impressions of pinnate leaves attributed to genera such as Sphenozamites from Permian-Triassic deposits, dating to over 250 million years ago (Ma). These leaf fossils, characterized by their wedge-shaped pinnae, suggest early cycad-like plants in Laurasian floras, though true stems assignable to the order appear in the Triassic around 230 Ma.^[67]^[68] During the Mesozoic, cycads including Cycas ancestors dominated many terrestrial ecosystems, comprising up to 20% of Jurassic-Cretaceous floras, with abundant reproductive structures like the cones of Beania from Jurassic sites in Europe and North America. Key fossil sites include the Morrison Formation in the USA, where petrified trunks of extinct relatives such as Cycadeoidea preserve cycad-like anatomy from the Late Jurassic (approximately 150 Ma), indicating diverse woodland communities alongside conifers and ferns.^[68]^[69]^[70] Fossils closely resembling the modern genus Cycas first appear in the Paleogene, with leaf impressions showing similar morphology in Eocene deposits (around 47 Ma) from India, China, and Europe, such as Cycas fushunensis from northeast China and records from Bulgaria and Britain. A leaf fossil from the Miocene of northern South Australia, described in 2025, represents the first record of Cycas from that continent. These Paleogene and Neogene occurrences in Asia and Europe demonstrate a shift toward more modern forms in subtropical to temperate settings.^[71]^[72]^[73] Cycads, including lineages leading to Cycas, survived the Cretaceous-Paleogene (K-Pg) boundary extinction event around 66 Ma, with post-extinction records showing continued presence in Paleocene-Eocene floras, though overall diversity declined as angiosperms rose to dominance in the Cenozoic. This survival is evidenced by seedling and adult foliage in early Paleocene sites, marking a transition to reduced ecological roles.^[68]^[74]^[42]

Divergence and speciation

The genus Cycas, representing the sole member of the family Cycadaceae, diverged from other cycad lineages (Zamiaceae) during the late Carboniferous to early Permian period, approximately 300 million years ago, as part of the ancient radiation of cycads following their split from gnetophytes and other gymnosperms.^[37] This early divergence established Cycas as a distinct clade adapted to tropical and subtropical environments, with molecular dating supporting a stem age for Cycadaceae around 295–330 million years ago based on fossil-calibrated phylogenies.^[42] The crown age of the Cycas genus itself, marking the onset of diversification among extant lineages, is estimated at about 12 million years ago in the late Miocene based on earlier studies, though more recent phylogenomic analyses suggest older dates ranging from 43–69 Ma in the Paleogene.^[30]^[42]^[75] Major speciation events within Cycas occurred during the Miocene, particularly in Indochina and Australia, driven by tectonic uplifts including the Himalayan orogeny and the stabilization of the Sahul shelf.^[30] These processes fragmented habitats and created isolated refugia, with vicariance playing a key role in the separation of lineages as Gondwanan landmasses fully disassembled earlier in the Mesozoic, though Cycas-specific patterns involved post-Gondwanan dispersals across Southeast Asia and into Australasia around 1.5–2 million years ago.^[42] Pleistocene bursts further accelerated diversification, with sections like Cycas and Stangerioides radiating within the last 1–2 million years, leading to high endemism in montane and coastal regions; many species arose during these Quaternary fluctuations.^[30] Key drivers of Cycas speciation include Miocene-Pliocene climate shifts toward aridification, which promoted habitat specialization in dry valleys and sclerophyllous woodlands, coupled with fragmentation from tectonic activity and sea-level changes.^[76] Low gene flow, constrained by specialized beetle pollination and limited seed dispersal (often <1 km), fostered genetic isolation and rapid allopatric speciation, resulting in numerous narrow endemics.^[77] Interspecific hybridization is rare across most Cycas lineages due to strong reproductive barriers, though occasional admixture occurs in sympatric zones, minimally impacting overall divergence.^[78] These patterns underscore the relictual status of Cycas, contributing to their vulnerability through small population sizes and limited adaptability to ongoing anthropogenic pressures.^[30] This diversification explains the genus's elevated extinction risk, as young lineages lack the evolutionary resilience of more ancient groups.^[79]

Human interactions

Cultivation and uses

Cycas revoluta, commonly known as the sago palm, is widely cultivated as an ornamental plant in subtropical and temperate regions, particularly in USDA hardiness zones 9 through 11, where it thrives in sandy, humusy, well-drained soils with partial shade.^[80]^[6]^[81] It is propagated primarily through seeds or offsets, though seed production requires both male and female plants for pollination.^[6] The plant exhibits very slow growth, often taking decades to reach maturity, with young specimens reaching 2-3 feet in height after several years and potentially up to 20 feet over a century.^[80]^[81] As a landscape feature, it serves as a specimen plant, border accent, or container subject, valued for its fern-like fronds and prehistoric appearance.^[80]^[6] Commercial production of starch from Cycas species, particularly C. revoluta, involves extracting sago from the pithy trunk, a process that requires thorough washing and detoxification due to the presence of toxic compounds like cycasin.^[82] However, such production remains limited compared to sago derived from true palms like Metroxylon sagu, as the raw material from cycads contains high levels of azoxyglycosides, including cycasin, which are carcinogenic and neurotoxic if not properly processed.^[83]^[84] In traditional practices, various Cycas species have been used medicinally, such as bark decoctions from C. revoluta for treating rheumatism and bone pain in parts of India and the Philippines, and leaves in Chinese medicine for wound healing and inflammation.^[85]^[86] Leaves are also employed ceremonially in rituals across Southeast Asia and India, symbolizing prosperity or used in decorations.^[85] Despite these applications, all parts of Cycas plants are toxic, with seeds containing the highest concentrations of cycasin and related azoxyglycosides, which can cause vomiting, liver damage, seizures, and potentially fatal outcomes upon ingestion.^[83]^[84]^[6] Cultivation challenges include susceptibility to pests such as the cycad aulacaspis scale (Aulacaspis yasumatsui), an armored insect that feeds on sap and can kill plants within a year if unmanaged, and sensitivity to overwatering, which leads to root rot from pathogens like Phytophthora.^[6]^[87]^[88] Global trade in Cycas plants is significant, with millions of specimens exchanged annually under CITES regulations to prevent overexploitation, though illegal trade persists.^[89]^[90]

Conservation status

Approximately 71% of the approximately 117 recognized species in the genus Cycas are classified as threatened with extinction on the IUCN Red List, with around 42% categorized as Endangered or Critically Endangered based on assessments up to 2025.^[91]^[4] The primary threats to Cycas species include habitat loss driven by deforestation and agricultural expansion, as well as illegal collection for the horticultural trade, which has led to severe population declines in many regions.^[92]^[93] Legal protections for Cycas species are provided through the Convention on International Trade in Endangered Species of Wild Fauna and Flora (CITES), with one species, Cycas beddomei, listed in Appendix I, prohibiting commercial international trade, while the majority fall under the family-wide Appendix II listing for Cycadaceae, requiring permits to regulate trade and prevent overexploitation.^[94]^[95] Additional safeguards include national legislation, such as India's Wildlife Protection Act for endemic species like C. beddomei and Australia's Environment Protection and Biodiversity Conservation Act for species like Cycas megacarpa.^[96]^[97] Regional conservation challenges vary, with poaching for ornamental horticulture posing acute risks in hotspots like Vietnam and China, where fragmented populations of up to 20 endemic Cycas species face ongoing decline.^[92] In Australia, altered fire regimes exacerbate threats to species such as C. megacarpa, disrupting natural regeneration cycles in native woodlands.^[97] Ex situ conservation efforts are critical, with botanic gardens and seed banks maintaining collections of over 50 Cycas species to support genetic diversity preservation.^[98] Recovery initiatives include reintroduction programs, such as those for C. megacarpa in Queensland, Australia, involving translocation and habitat restoration to bolster wild populations, alongside ongoing monitoring through the IUCN Red List assessments. The 2024-2025 IUCN SSC Cycad Specialist Group report highlights progress in Red List assessments and conservation actions for over 50 Cycas species, including ex situ collections and reintroduction programs.^[97]^[98] Climate change is projected to intensify pressures, potentially rendering 30% more Cycas habitats unsuitable by 2050 due to shifting temperature and precipitation patterns, further emphasizing the need for adaptive management strategies.^[99]

References

[1]
The distribution, diversity, and conservation status of Cycas in China
As ancient gymnosperm and woody plants, cycads have survived through dramatic tectonic activities, climate fluctuation, and environmental variations making them ...4. Threats To Cycas · 5. Conservation Efforts · Table 3
[2]
Cycas | North Carolina Extension Gardener Plant Toolbox
Cycas is a palm-like plant with 113 species, some growing to 40 feet. It has uncoiled leaves, and is very poisonous, with seeds having the highest toxin ...
[3]
Cycas L. | Plants of the World Online | Kew Science
Cycas L. is a genus native to Kenya to Mozambique and W. Pacific, with 117 accepted species, and belongs to the Cycadaceae family.
[4]
Cycas - an overview | ScienceDirect Topics
Cycas refers to a genus of palmlike woody plants within the order Cycadales, characterized by their presence in tropical and subtropical dry regions and the ...
[5]
Cycas revoluta - North Carolina Extension Gardener Plant Toolbox
Sago palm is a tropical and sub-tropical showy evergreen member of an ancient plant family known as cycads (Cycadaceae), dating back 200 million years ago.
[6]
Cycas: External Features and Different Parts - Biology Discussion
10. Leaves are of two types: foliage leaves and scaly leaves. 11. Foliage leaves are green, large, pinnately compound and may reach up to 3 ...
[7]
Male Cone of Cycas and Pinus | Gymnosperms - Biology Discussion
Each male cone is oval or conical in shape in cycas and very large measuring up to 80 cm or more in length.Missing: size | Show results with:size
[8]
Cycadaceae - an overview | ScienceDirect Topics
All cycads have pollen cones or strobili (also called male cones/strobili). ... Extant cycad cone. Bar=4.0 cm. (Courtesy P. Ryberg.) Leaves and Petioles.
[9]
The Cycad Page - Cycadaceae, Stangeriaceae, Zamiaceae
Oct 23, 2023 · Cycads have a cylindrical caudex or trunk, sometimes almost entirely subterranean, with a spiky appearance from persistent petiole bases on ...
[10]
[PDF] DEVELOPMENTAL ANATOMY OF CORALLOID ROOTS IN CYCADS.
Coralloid roots are apogeotropic, above-ground, dichotomously branched roots in cycads, often with an algal zone and a cortex, and may be found below ground.
[11]
Perspectives on Endosymbiosis in Coralloid Roots: Association of ...
Aug 14, 2019 · Nitrogen fixation in Nostoc, the dominant species symbiotic to cycads coralloid roots (Gehringer et al., 2010), occurs in structures called ...
[12]
[PDF] cycas - ADP College
In internal structure, coralloid root shows the presence of epidermis, cortex and stele. • Epidermis of younger coralloid root is single layered, thin walled.
[13]
[PDF] Distribution of Cycas: - Ramsaday College
A single foliage leaf is pinnately compound. It is unipinnate and paripinnate. Each leaf has 80-100 pairs of leaflets which are arranged on both the sides of ...
[14]
[PDF] Structure, systematic position and life cycle of Cycas
Cycas is a slow-growing, long-lived, palm-like plant with a short, unbranched stem, large compound leaves, and a tap root system with coralloid roots. It has a ...
[15]
Leaflets of Cycadaceae - jstor
The anatomy of the leaflets is typically xerophytic. The epi- dermis is strongly cutinized, and has sunken stomata which are confined to the under surface ...
[16]
Reproductive Mechanisms in Ginkgo and Cycas: Sisters but not Twins
In Cycas and Ginkgo the sperm cells are not delivered by the pollen tube, hence they should swim in an appropriate aqueous medium toward the egg cell. The ...
[17]
CENTRIOLE REPLICATION II. Sperm Formation in the Fern ...
Sperm formation in the cycads is a long process taking place within the pollen tube during the several months between pollination and fertilization. A time.Missing: anatomy | Show results with:anatomy
[18]
CYCAD Definition & Meaning - Merriam-Webster
Etymology. New Latin Cycad-, Cycas, genus name, from Greek kykas, manuscript variant of koïkas, accusative plural of koïx, a kind of palm. First Known Use.
[19]
Cycad - Etymology, Origin & Meaning
Cycad, from Modern Latin Cycadaceae (1845), originates from Greek kykas (a scribal error for koikas "palm trees"), meaning a gymnospermous plant order.Missing: genus | Show results with:genus
[20]
Cycas - Wiktionary, the free dictionary
From a mistranscription of the Ancient Greek name of a palm mentioned by Theophrastus, κοικας. Proper noun. Cycas f. A taxonomic genus within the family ...
[21]
The Families and Genera of Cycads: A Molecular Phylogenetic ...
Linnaeus recognized two cycad species in two genera, Cycas circinalis and Zamia pumila. The number of species described gradually increased as exploration ...
[22]
Cycas circinalis () description - The Gymnosperm Database
Mar 3, 2023 · Described 1658 from the Malabar Coast in southwest India and is the type species of Cycas. Due to its wide range and sporadic dispersal, many ...
[23]
Cycas curranii (J.Schust.) K.D.Hill - World Flora Online
2 Julius Schuster (1886-1949); 3 Ken Hill (1948-2010); 4 The Plant List v1.1 ... Classification. 2 higher taxa · Cycadophyta Bessey · Cycadopsida Brongn ...
[24]
Hill, Kenneth. 2008. "The genus Cycas (Cycadaceae) in China ...
The comprehensive account of the genus by de Candolle (1868) summarised work to that point, and recorded no cycad species from the region of China. Pilger ...
[25]
[PDF] Character Evolution, Species Recognition and Classification ...
A cylindrical pollen cone was regarded by de Laubenfels and Adema (1998) as a diagnostic character for the new genus Epicycas, although the cylindrical state ...
[26]
A Review of Taxonomic Concepts and Species Delimitation in ...
Nov 16, 2023 · The formal taxonomic history of Cycadales began with the description of Cycas circinalis by Carl von Linnaeus (Linnaeus, 1763). The rate of ...
[27]
Cycas | Description, Cycad, Uses, Species, & Facts | Britannica
Members of the genus Cycas can grow as trees 12 metres (40 feet) or more in height. Their large compound leaves are dark green and circinate (uncoiling as fern ...
[28]
Phylogeny of the gymnosperm genus Cycas L. (Cycadaceae) as ...
Cycas L. is the sole genus of Cycadaceae, and comprises 115 species (Calonje et al., 2017). This gymnosperm genus is mainly distributed in tropical and ...<|separator|>
[29]
The Cycad Genus Cycas May Have Diversified From Indochina and ...
Historical Biogeography Our analysis points to Indochina (∼99%) as the origin of the genus Cycas, which dated back to around 12 Ma (node I, Figure 2).Missing: Linnaeus modern
[30]
Genetic diversity, structure and distribution of Australian Cycas
Sep 11, 2019 · The genus Cycas includes about 117 species, 32 of which are native to Australia and 20 occur only in the subtropical and tropical regions of Queensland.
[31]
[PDF] A NEW BOOK ON THE CYCADACEAE
In 'Cycads of Vietnam', each of the 27 species is described in detail with line drawings, maps and numerous photographs illustrating points of interest.<|separator|>
[32]
[PDF] The genus Cycas (Cycadaceae) in China - PlantNET
This section is defined by the firm, waxy microsporangiate cones and microsporophylls, the pectinate megasporophyll apices, the tomentose ovules, and the red ...Missing: shape | Show results with:shape
[33]
Cycadaceae and Cycas (Cycad family and genus) description
Feb 22, 2025 · In this treatment there are 88 species, but so far there has been no comprehensive generic study. The species are listed here, with links to ...
[34]
A phylogeny of cycads (Cycadales) inferred from chloroplast matK ...
Phylogenetic relationships among the three families and 12 living genera of cycads were reconstructed by distance and parsimony criteria using three markers.
[35]
The Cycas genome and the early evolution of seed plants - Nature
Apr 18, 2022 · Here, we report the 10.5-Gb reference genome of Cycas panzhihuaensis, complemented by the transcriptomes of 339 cycad species.
[36]
Cycas L. - Cycadlist.org
First published in: Sp. Pl. · Etymology: From the Greek Koikas, a kind of palm · Synonyms: · Description: Habit: dioecious palm like shrubs ...
[37]
(PDF) African Cycad Ecology, Ethnobotany and Conservation
Aug 9, 2025 · Africa hosts a rich assemblage of cycads: 66 Encephalartos species, Stangeria eriopus and Cycas thouarsii. Most Encephalartos and S. eriopus adults appear to ...
[38]
(PDF) The genus Cycas (Cycadaceae) in Indonesia - ResearchGate
... genus by de Candolle (1868) recorded C. circinalis. var. javana ... This leaf morphology is more consistent with extant Cycas species of the former section ...
[39]
Molecular phylogeny of cycads inferred from rbcL sequences
The rbcL sequences also indicate that the colonisation of Madagascar by Cycas thouarsii occurred only recently as the sequences of C. thouarsii and Cycas ...
[40]
Reconciling fossils with phylogenies reveals the origin and ...
Jun 11, 2023 · A new cycad stem from the Cretaceous in Argentina and its phylogenetic relationships with other Cycadales. Botanical Journal of the Linnean ...
[41]
[PDF] Cycads - IUCN Portal
The main centres of diversity are Vietnam (24 species),. China (21), Thailand (10), Indonesia (7), Papua New. Guinea (PNG) (6), Philippines (5), and Malaysia ...
[42]
Investigating the demographics and intrapopulation spatial patterns ...
Oct 13, 2017 · Cycas megacarpa K.D.Hill is an endangered cycad endemic to central Queensland, Australia. Populations of this species have been impacted by ...
[43]
Life History and Ecology of the Cycads
Cycads grow in a number of different habitats. Species may be found as components of the forest understory in both rainforests and seasonally dry forests, or ...Missing: adaptations fire fixation
[44]
Habitat Suitability and Driving Factors of Cycas panzhihuaensis in ...
Sep 6, 2025 · This elevation-climate synergy illustrates the regulatory role of topography on regional climatic gradients and reveals the complex ecological ...
[45]
The Nitrogen-Fixing Abilities of Cycads - In Defense of Plants
Oct 11, 2017 · Long before the first legumes came onto the scene, the early ancestors of Cycads were hard at work fixing atmospheric nitrogen.Missing: genus adaptations fire tolerance
[46]
Mycorrhizae Are Present in Cycad Roots - jstor
We describe the occurrence of arbuscular mycorrhizae in the roots of Zamia pumila and. Dioon edule. Seedlings were grown on native, unsterilized soil taken ...
[47]
Cycad plants provide an important 'ecosystem service' - ScienceDaily
Jul 27, 2020 · At least two cycad species share nitrogen and carbon through the soil, thereby creating habitable environments for other organisms.Missing: genus adaptations fire
[48]
Ethnobotany of Mexican and northern Central American cycads ...
Jan 18, 2019 · Their unique adaptations include nitrogen-fixing coralloid roots [10], extreme fire- and drought-tolerance, and the capacity to produce ...<|separator|>
[49]
[PDF] National Multi-species Recovery Plan for the cycads, Cycas ...
Four genera of cycads: Bowenia, Cycas, Lepidozamia and Macrozamia occur in Australia, 74 species overall. Queensland is a major centre of diversity, with 13 ...
[50]
[PDF] Cycas hoabinhensis, an endangered stenoendemic of Vietnam
The northern part of Vietnam is a shelter for many cycads. Eleven species have been found here in different habitats. Three species are stenoendemics in ...
[51]
[PDF] The ecology of Cycas armstrongii and management of fire in ...
the apparent tolerance of cycads to fire it is highly likely that the great abundance of cycads in northern Australia is associated with the prevailing ...
[52]
Cycads: their evolution, toxins, herbivores and insect pollinators
Because pollination by beetles and by thrips has now been detected in several modern cycads, it is attractive to speculate that some insects and cycads had ...
[53]
Cycadaceae) Species Offered as Larval Food Influences Fecundity ...
Dec 6, 2017 · Indeed, conservation of cycad species is important partly because they embody a critical function in the life histories of other organisms.Missing: keystone allelopathy
[54]
The Cycas genome and the early evolution of seed plants - PMC
Apr 18, 2022 · The Evolution of flagella related genes in embrophyta. Extended Data Fig. 7 · Open in a new tab. (a) Sketch of the Cycas sperm. (b) Schematic ...
[55]
Reproductive Mechanisms in Ginkgo and Cycas: Sisters but not Twins
Jul 31, 2023 · In Ginkgo and Cycas fertilization occurs via zoogamy, with flagellated sperm cells swimming toward the archegonia for penetrating the egg cell (
[56]
[PDF] Taxonomic aspects and coning ecology of Cycas circinalis L ...
Jan 26, 2011 · Sexual reproduction involves cone and seed production ... Seed morphology in relation to dispersal, evolution, and propagation of Cycas ...
[57]
Is Cycas revoluta (Cycadaceae) wind‐ or insect‐pollinated?
May 1, 2007 · We conclude that C. revoluta relies on both wind (anemophily) and insect pollination (entomophily), although such anemophily is restricted to female trees.
[58]
Beetle Pollination of Cycads in the Mesozoic - ScienceDirect.com
Sep 10, 2018 · Modern cycads are principally pollinated by beetles, and rarely by thrips or moths [3]. Their beetle pollinators mainly include cucujoids ( ...
[59]
Comparative Biology of Cycad Pollen, Seed and Tissue - NIH
Jul 5, 2018 · Pollination may occur three to seven months prior to fertilization. For example, in Encephalartos altensteinii it takes between 99 and 120 days ...
[60]
[PDF] Embryo Development and Germination of Cycas Seeds
Germination of Cycas revoluta seed is slow and erratic when planted immediately after collection, and most lose viability in a few months.
[61]
[PDF] Life-History of <Emphasis Type="Italic">Cycas circinalis </Emphasis ...
This is simple polyembryony (Rao, 1964). It is seen from the above description, the embryo proper which ulti- mately gives rise to the stem, root and the ...
[62]
[PDF] THE PROPAGATION OF CYCADS-A GAME FOR YOUNG PEOPLE?
Cycad propagation includes hand pollination, pollen transfer, seed storage, scarification, division, and cutting stem pieces to regenerate roots.<|control11|><|separator|>
[63]
Observations on Vegetative Branching in Cycads - ResearchGate
Aug 7, 2025 · Vegetative branching in cycads occurs via two known mechanisms: isotomous branching of the shoot apex or adventitious branching associated with ...
[64]
[PDF] Efficacy of in vitro tissue culture versus stem cuttings for propagation ...
The development of a root system was observed within 20 to 30 days of planting with 80% survival rate. Of the 400 or so stem cuttings taken, 319 plants were ...
[65]
Effect of medium culture on germination and plant development of ...
The results revealed that the highest GP (73%) was obtained with SH medi um while the GP was around 57% with MS medium (Table 1). A higher regeneration ...
[66]
Review on Conservation of Endangered Cycad Cycas beddomei Dyer
May 19, 2025 · The study also underlines the importance of technologies, such as tissue culture and cryopreservation, in germplasm propagation and conservation ...
[67]
[PDF] Paleozoic Origin of the Cycads - USGS Publications Warehouse
Cycas-a morphological misconception. Its bearing on the phylo~ny and the classification of the Cycadophyta: Acta Botanic~ Neerlandica, v. 12, p. 119-128 ...
[68]
Fossil Reord of the Cycads
Cycads are an ancient group of seed plants. They first appeared in the Pennsylvanian and so have existed for approximately 300 million years.
[69]
Morrison Formation - Dinosaur National Monument (U.S. National ...
Mar 23, 2024 · Instead, the Morrison Formation has yielded numerous fossilized ferns, cycads, ginkos, horsetails, and large conifer trees. As big as the ...
[70]
[PDF] THE FOSSIL CYCADS - The Palaeontological Association
Fossil cycads are a large, indefinite assemblage of plant organs, mostly from the Mesozoic era, with a large number of genera and species.
[71]
(PDF) Cycas fushunensis sp nov (Cycadaceae) from the Eocene of ...
This i-LDG pattern is remarkable, given fossils assigned to the genus Cycas are all found in east and northeast Asia's temperate regions since the Eocene, when ...
[72]
[PDF] The Fossil Cycads
Fossil cycads are named for leaves, cones, and stems, often found as storm debris, and are clues to the past.
[73]
First cycad seedling foliage from the fossil record and inferences for ...
Jul 10, 2019 · We describe a compression fossil of cycad eophylls with co-occurring fully developed leaves of adult specimens from the early Palaeocene (ca 63.8 Ma) Castle ...
[74]
Cenozoic topography, monsoons and biodiversity conservation ...
In mid Miocene times, before the Himalaya reached their current elevation, sediment infilling and compressional tectonics raised the floor of the central valley ...
[75]
ISSR Variation in the Endemic and Endangered Plant Cycas ... - NIH
The level of gene flow via seed and pollen is constrained by the low migratory capabilities of the pollinators and the seed‐carriers. The gene flow distance ...
[76]
Genome-Wide Evidence for Complex Hybridization and ...
Aug 30, 2021 · Low genetic diversity is more likely an inherent characteristic ... Our study provides genomic evidence of interspecific gene flow in Cycas ...
[77]
Cycads are not “living fossils” from Dinosaur Age - Berkeley News
Oct 21, 2011 · “They evolved independently of dinosaurs only 12 million years ago. The recent radiation of cycads radically changes our view of these ...Missing: genus | Show results with:genus
[78]
Cycas revoluta - Plant Finder - Missouri Botanical Garden
Arching pinnate leaves (to 3-7' long depending on age) form a loose, feather-like rosette with leaflets to 7" long. Each leaf has a large mid-rib with very ...
[79]
Sago Palm Outdoor Care: Can Sagos Grow In The Garden
Feb 16, 2021 · Growing Sago palms outdoors is only suitable in USDA zones 9 to 11. That means they cannot survive sustained freezing temperatures and are more suited to ...
[80]
[PDF] Sago.pdf - doc-developpement-durable.org
Sago is extracted from the sago cycad by cutting the pith from the stem, root and seeds of the cycads, grinding the pith to a coarse flour and then washing it ...
[81]
Cycasin - an overview | ScienceDirect Topics
Cycas revoluta is poisonous to almost all types of animals. All parts of this plant are toxic; however, seeds contain maximum cycasin component, a potent toxin.
[82]
Cycasin | C8H16N2O7 | CID 5459896 - PubChem
Acute symptoms produced after consumption of untreated Cycas seeds are due to azoxyglycosides, especially cycasin, although the toxic dose depends on the animal ...
[83]
Oliba / Cycas revoluta / OLIVA - StuartXchange
Despite known toxicities, Cycad stems and seeds are used for high blood pressure, headaches, congestion, rheumatism and bone pain. • Leaves used in the ...
[84]
Cycads: A comprehensive review of its botany, traditional uses ...
Jan 28, 2024 · In Chinese traditional medicine, the leaves of cycads are particularly revered for their profound healing capabilities. This meticulous review ...
[85]
Cycad scale: a threat to wild and cultivated cycads - UF/IFAS Pest Alert
Jul 18, 2017 · Armored scales are small insect pests that use a straw-like mouthpart to suck out plant juices, have a hard exterior like a shell, and in high numbers can ...
[86]
Sago Palm Diseases And Pests - Common Problems With Sago Palm
Jun 18, 2021 · Phytophthora loves compacted, poor draining, overwatered soil. Make sure you plant your sago palm in good draining soil and do not overwater it.
[87]
[PDF] Review of Significant Trade Cycads - CITES
More than 50% of all cycad species occur in just three countries (Australia, Mexico and South Africa) (see Figure 2) and the ten countries with the highest ...Missing: count | Show results with:count<|control11|><|separator|>
[88]
US Botanic Garden and The Huntington Join Global Launch of ...
Oct 9, 2025 · Plants are trafficked at a higher volume than animals each year, with succulents, cacti, cycads, and orchids among the most frequently targeted.Missing: Cycas | Show results with:Cycas<|control11|><|separator|>
[89]
IUCN Red List of Threatened Species
Three Arctic seal species moved closer to extinction in the latest update of the IUCN Red List. The 2025-2 update also reveals more than half of bird species ...About · 3.1 · Searching The IUCN Red List · Citing The IUCN Red ListMissing: Cycas | Show results with:Cycas
[90]
Summary Statistics - IUCN Red List of Threatened Species
The IUCN Red List is updated. For each Red List update, IUCN provides summaries of the numbers of species in each category, by taxonomic group and by country.Missing: Cycas | Show results with:Cycas
[91]
Safeguarding China's threatened cycads: Strategies to combat ...
Jul 25, 2025 · Around 20 cycad species remain in China, beset with highly restricted distributions and small, fragmented, declining and threatened populations.
[92]
Cycads: the primeval plants getting rarer – and harder to protect
May 17, 2023 · They are disappearing as their tropical forest habitats are rapidly vanishing, and they also face extinction from an illegal multimillion-pound global trade in ...
[93]
Appendices | CITES
Species included in these Appendices are referred to: a) by the name of the species; or b) as being all of the species included in a higher taxon or designated ...
[94]
[PDF] CITES and Cycads: a user's guide - Kew Gardens
This guide is a training tool for understanding CITES and its application to cycads, covering the Convention on International Trade in Endangered Species.
[95]
Cycas circinalis - CITES
Cycas circinalis ; Family. Cycadaceae ; Rank. Species ; Listing. II ; Full note. **II** [FAMILY listing Cycadaceae spp.] Except the species included in Appendix I.
[96]
National Multi-species Recovery Plan for the cycads, Cycas ...
Oct 3, 2021 · The plan covers cycads Cycas megacarpa, Cycas ophiolitica, Macrozamia cranei, Macrozamia lomandroides, Macrozamia pauli-guilielmi, and ...Missing: reintroduction | Show results with:reintroduction
[97]
None
### Summary of Conservation Status for Cycas Genus (2024-2025 IUCN SSC Cycad SG Report)
[98]
Identifying Protected Areas Suitable for Conservation of Cycas ...
Out of 1938 protected areas identified in the 10 southeast countries, only 190 protected areas would remain suitable by the end of 2050 under climate change ...