Some cycads are defined by their leaves, others by their caudex shape. Cycas chamaoensis is defined by its address: a single granite mountain — Khao Chamao (เขาจะเม้า) — in Rayong Province, southeastern Thailand, roughly 200 km southeast of Bangkok. That is the entire world range of this species. One mountain, one cycad. Within that micro-range, however, Cycas chamaoensis is no timid rarity hiding in cliff crevices. It is a giant — arborescent, trunk to 10 m in exceptional specimens, with a crown of over 60 long, stiff fronds, and male cones up to 60 cm long. It is one of the largest and most imposing cycads in the entire Thai flora, confined to the smallest possible geographic footprint. This paradox — maximum stature on minimum real estate — makes it one of the most compelling species in the genus Cycas for anyone interested in the intersection of biogeography, morphology, and vulnerability.
Quick facts
| Scientific name | Cycas chamaoensis K.D.Hill |
| Family | Cycadaceae |
| Section | Indosinenses |
| Common names | Chamao cycad, Chamao Hill cycad |
| Origin | Southeastern Thailand: Khao Chamao mountain, Khao Chamao–Khao Wong National Park, Rayong/Chantaburi provinces |
| Altitude | Approximately 200–500 m |
| Habitat | Crevices in bare granite rock slopes, in full sun |
| Caudex height | Arborescent; erect or decumbent; to 5–10 m tall in exceptional specimens |
| Leaf length | 120–250 cm (4–8 ft); more than 60 leaves per crown |
| Cold hardiness | Estimated USDA zone 10a–10b (tropical; frost-free) |
| IUCN status | Critically Endangered (CR A2ad; B1ab(i,ii,iv,v); C2a(i); D) |
| CITES | Appendix II (all Cycas species) |
Taxonomy
Cycas chamaoensis was described by K.D. Hill in 1999, in his revision of the genus Cycas in Thailand (Hill & Yang, Brittonia). The holotype is deposited at NSW (National Herbarium of New South Wales, Sydney). The specific epithet refers to Khao Chamao (เขาจะเม้า), the granite mountain that is the species’ only known natural habitat. The species was described alongside four other Thai endemics new to science — Cycas clivicola, Cycas litoralis, Cycas nongnoochiae, and Cycas tansachana — reflecting the remarkable cycad diversity of Thailand, much of it confined to isolated mountain endemics separated by lowland plains where only the widespread Cycas siamensis occurs.
Cycas chamaoensis is placed in section Indosinenses, allied to Cycas pectinata. Hill & Yang (1999) note that the large megasporophylls with a strongly dilated lamina distinguish both Cycas pectinata and Cycas chamaoensis from Cycas clivicola and from Cycas siamensis (which differs further by its thickened bark). The precise phylogenetic relationship between Cycas chamaoensis and Cycas pectinata remains to be resolved by molecular data.
Ecology, distribution, and conservation
Distribution
Cycas chamaoensis is known only from a single mountain: Khao Chamao, located in the Khao Chamao–Khao Wong National Park, near the town of Klaeng in Rayong Province (with the national park boundary extending into adjacent Chantaburi Province). The mountain is a granite inselberg — an isolated rocky massif rising from the surrounding lowland plains — approximately 200 km southeast of Bangkok.
The total extent of occurrence is measured in square kilometers — probably less than 10 km². This makes Cycas chamaoensis, alongside Cycas elephantipes (Chaiyaphum) and Cycas nongnoochiae (Chon Buri), one of the most geographically restricted cycads in mainland Southeast Asia. Unlike Cycas elephantipes, which occurs on multiple sandstone mesas within a single district, Cycas chamaoensis appears to be confined to a single mountain — the ultimate in point-endemic distribution.
Habitat
The species grows in full sun, in crevices in bare granite rock slopes — an exposed, lithophytic habitat strikingly similar to that of Cycas ferruginea on limestone in the Sino-Vietnamese border region, and to Cycas elephantipes on sandstone in Chaiyaphum. Hill & Yang (1999) describe it as growing “in crevices in bare rock slopes” on the steep north and northwest faces of Khao Chamao.
The granite substrate is acidic, siliceous, nutrient-poor, and provides excellent drainage. The full-sun exposure on bare rock creates a hot, dry microclimate during the day, with rapid radiative cooling at night. This is not a forest-floor species — it is an open-rock specialist, fully exposed to sun, wind, and seasonal drought. Plants are also reportedly common in gardens in the area around Klaeng, indicating a history of local cultivation from wild-collected material.
Climate in the native range
| Parameter | Value |
|---|---|
| Mean annual temperature | 27–29°C |
| Summer maximum (March–May) | 34–38°C; moderate to high humidity |
| Winter minimum (December–January) | 18–22°C; frost absent |
| Annual rainfall | 1,400–2,000 mm (monsoon peak May–October; drier November–March) |
| Dry season | November–March (3–4 months; less severe than the Isan dry season of Cycas elephantipes) |
The climate is tropical, warm year-round, with a distinct but moderate dry season. The southeastern Thai coast is more humid than the interior Isan plateau, receiving more rain and experiencing less extreme temperature fluctuations. Cycas chamaoensis is essentially a frost-free tropical species with no cold tolerance whatsoever.
Threats
- Illegal collection: the primary and most severe threat. The species’ spectacular size (tall trunk, dense crown, large cones) and its proximity to the Bangkok metropolitan area make it a prime target for the ornamental plant trade. Hill & Yang (1999) already flagged severe collection pressure at the time of description.
- Extremely restricted range: with a single mountain as its entire world, any local disturbance — fire, quarrying, landslide, disease outbreak — could eliminate a significant fraction of the global population in a single event.
- Aulacaspis scale: the cycad aulacaspis scale (Aulacaspis yasumatsui) is present in Thailand and is a potential threat to wild populations.
Conservation status
The IUCN Red List classifies Cycas chamaoensis as Critically Endangered (CR) under multiple criteria: A2ad (population decline >80%), B1ab (very small extent of occurrence with continuing decline), C2a(i) (small population with continuing decline), and D (very small population). This is the maximum possible set of CR criteria applied simultaneously — reflecting the species’ extreme vulnerability on every measurable axis.
The species falls within the boundaries of the Khao Chamao–Khao Wong National Park, which provides legal protection. However, enforcement against collection on steep, remote rock slopes is difficult. All Cycas species are listed under CITES Appendix II.
Morphology
Caudex — the giant of Thai cycads
Cycas chamaoensis is one of the largest Cycas species in mainland Southeast Asia. The trunk is arborescent, either erect or decumbent (leaning), reaching 5 to 10 m in height in exceptional wild specimens — a stature that rivals Cycas pectinata and exceeds most other Thai species. The trunk surface is smooth (not deeply fissured like Cycas elephantipes or thickened like Cycas siamensis), with persistent leaf bases. Trunk diameter is approximately 15–25 cm at the narrowest point.
The smooth, tall trunk growing from bare granite crevices — sometimes at dramatic angles on steep slopes — gives wild specimens a sculptural, almost gravity-defying quality.
Leaves
The crown is dense and large, carrying more than 60 pinnate leaves — one of the highest leaf counts in the Thai Cycas flora and a stark contrast to the sparse 4–7 leaf crowns of Cycas tanqingii. Each leaf is 120–250 cm long, ending in a terminal spine. The petiole is 30–60 cm long, glabrous, and partially spiny. Leaflets number 85–155 pairs, lanceolate, glabrous, and angled forward at 60–70° to the rachis.
The dense, large crown atop a tall smooth trunk creates a silhouette that approaches a palm in overall form — one of the most “tree-like” appearances in the genus.
Reproductive structures
Cycas chamaoensis is strictly dioecious.
Male cones are solitary, erect, spindle-shaped to narrowly ovoid, 50–60 cm long and 12–13 cm in diameter — among the largest male cones in the Thai Cycas flora. The color is orange. Microsporophylls bear a prominent apical spine.
Female megasporophylls are large (13–18 cm long), with yellow to grey tomentum, bearing 2–4 ovules each. The sterile lamina is long, almost circular, with numerous lateral spines — a strongly dilated lamina character shared with Cycas pectinata and diagnostic for the section Indosinenses affinity. Seeds have a yellow sarcotesta (3 mm thick) and a smooth sclerotesta.
Similar species
| Species | Key distinguishing features | Distribution |
|---|---|---|
| Cycas pectinata | Same section (Indosinenses); similarly large megasporophylls; wider distribution (NE India through Indochina to Yunnan); tomentose ovules; less restricted to a single mountain | Himalayan foothills to Yunnan — vastly wider range |
| Cycas elephantipes | Also a single-region Thai endemic; deeply fissured, swollen caudex base (diagnostic); sandstone substrate (not granite); shorter stature; Isan (NE Thailand) | Chaiyaphum Province, NE Thailand |
| Cycas siamensis | Widespread across Indochina; thickened, bottle-shaped bark (not smooth); typically shorter; various substrates including limestone; deciduous woodland | Myanmar through Thailand to Vietnam — ubiquitous |
| Cycas nongnoochiae | Another single-mountain Thai endemic (Chon Buri Province); shorter; limestone substrate; different megasporophyll | Khao Soi Dao area, Chon Buri — also SE Thailand |
The comparison between Cycas chamaoensis (granite, tall smooth trunk, section *Indosinenses*) and Cycas elephantipes (sandstone, swollen fissured base, section *Stangerioides*) illustrates the same principle seen throughout this species cluster: two Thai cycad endemics, both confined to isolated rocky outcrops, both critically threatened by collection, but morphologically and ecologically distinct — different substrates, different sections, different growth strategies. Central Thailand’s cycad diversity is distributed across isolated mountain “islands” separated by lowland plains where only *Cycas siamensis* persists.
Cultivation
| Aspect | Recommendation |
| Light | Full sun. The species grows on fully exposed bare granite rock faces. Maximum light in cultivation. |
| Substrate | Extremely well-drained, acidic to neutral, siliceous. Granite substrate in the wild — use coarse sand, pumice, granite grit, pine bark. pH 5.5–6.5. No limestone. |
| Watering | Regular during the growing season (monsoon equivalent); reduced in winter dry season. The granite-crevice habitat drains instantly — water should never pool. |
| Fertilization | Moderate. The species grows on nutrient-poor granite — light, slow-release feeding in spring and summer. |
| Cold hardiness | Frost-free only. USDA zone 10a–10b. The native range is tropical with no frost history. No cold tolerance. Heated greenhouse culture in any climate with frost. |
| Growth rate | Moderate to fast for a cycad under tropical conditions — the tall stature and dense crown suggest reasonable vigor. |
The space issue
A mature Cycas chamaoensis is a large plant. A trunk to 5–10 m topped by a crown of 60+ fronds, each 1.2–2.5 m long, requires a clear canopy span of approximately 4–5 m in diameter. This is not a windowsill cycad or a small-greenhouse specimen — it is a landscape-scale plant that needs tropical conditions and substantial room. In a large heated conservatory, a botanical garden glasshouse, or a frost-free tropical garden, it can be spectacular. In a small greenhouse, it is impractical.
Propagation
Propagation is from seed. The species is extremely rare in cultivation outside Thailand. Some plants are grown in Thai botanical gardens and private collections. Seeds or nursery-propagated plants are unlikely to be available from commercial nurseries outside Southeast Asia. Given the species’ Critically Endangered status, only legitimately sourced, nursery-propagated material should ever be acquired.
Pests and diseases
Standard Cycas pest profile: cycad aulacaspis scale is the main concern in tropical cultivation. Root rot from waterlogging — unlikely in the granite-crevice native habitat but possible in poorly drained containers. The dense crown (60+ leaves) may harbor mealybugs in the leaf axils.
Landscape use and collector interest
Cycas chamaoensis is a cycad for institutions and serious tropical collectors with substantial space. Its appeal lies in the combination of maximum stature (one of the tallest *Cycas* in Southeast Asia), minimum range (a single mountain), and maximum threat (CR on every criterion). For tropical botanical gardens, it represents a flagship species — a plant that embodies the conservation crisis of Southeast Asian cycads in a single dramatic individual. For the private collector in a frost-free climate, a seed-grown Cycas chamaoensis is a genuine rarity that few collections in the world possess.
The pairing of Cycas chamaoensis with Cycas elephantipes in a collection would illustrate the two extremes of Thai cycad morphology: the tallest smooth trunk in the flora alongside the most dramatically swollen and fissured base — both confined to single-district endemics, both Critically Endangered, both growing on acidic rock, yet utterly different in form.
Frequently asked questions
How tall can Cycas chamaoensis grow?
Exceptional wild specimens on Khao Chamao reach up to 10 m in trunk height, making it one of the tallest Cycas species in Southeast Asia. In cultivation, growth will be significantly slower and maximum height lower, but the species’ arborescent habit means it will eventually outgrow any small greenhouse.
Is Cycas chamaoensis the same as Cycas pectinata?
No. Both belong to section Indosinenses and share large megasporophylls with strongly dilated laminas, but they are distinct species. Cycas chamaoensis is endemic to a single granite mountain in southeastern Thailand, while Cycas pectinata has a vast distribution from northeastern India through Indochina to Yunnan. They differ in megasporophyll details and geographic range.
Why is Cycas chamaoensis Critically Endangered?
It meets CR criteria on every measurable axis: population decline over 80% (A2ad), very small extent of occurrence with continuing decline (B1ab), small population with continuing decline (C2a), and very small total population (D). The combination of a single-mountain range and severe collection pressure for the ornamental trade makes it acutely vulnerable.
Where can I buy Cycas chamaoensis?
It is extremely rare in cultivation outside Thailand and is unlikely to be available from commercial nurseries in the West. Some Thai botanical gardens and specialist growers may hold specimens. Given its Critically Endangered status, only legitimately sourced, nursery-propagated material should be considered. Never purchase wild-collected specimens.
Online resources
- POWO — Plants of the World Online (Kew): Cycas chamaoensis — accepted name, native range (SE Thailand).
- The World List of Cycads: Cycas chamaoensis — etymology (Khao Chamao mountain), type (HT: NSW), IUCN status (CR A2ad; B1ab(i,ii,iv,v); C2a(i); D).
- GBIF — Global Biodiversity Information Facility: Cycas chamaoensis — occurrence data.
- Hill, K.D. & Yang, S.L. (1999) — Brittonia: The genus Cycas (Cycadaceae) in Thailand. Brittonia, 51(1), 48–73. The original species description, with morphological comparison to Cycas pectinata and Cycas siamensis, habitat description, and distribution map.
References
- Haynes, J.L. (2022). Etymological compendium of cycad names. Phytotaxa, 550(1), 1–31.
- Hill, K.D. & Yang, S.L. (1999). The genus Cycas (Cycadaceae) in Thailand. Brittonia, 51(1), 48–73.
- Osborne, R., Calonje, M.A., Hill, K.D., Stanberg, L. & Stevenson, D.W. (2012). The world list of cycads. Memoirs of the New York Botanical Garden, 106, 480–510.
- Whitelock, L.M. (2002). The Cycads. Timber Press, Portland.