Woody > Cycas > Cycas thourasii > Cycas thourasii
Cycas thourasii
Origin: The Madagascar cycad is a coastal plant. It is most common in Madagascar but can also be found along the coasts of Mozambique, Kenya, Tanzania, and the Comoro Islands. A popular theory proposes that the Madagascar cycad was introduced to Africa and the Comoros by Arab merchants, as it was to Mauritius and the Seychelles.
Mike's
Opinion
"
A large, fast-growing, palm-like plant, Cycas thouarsii can be found growing in Madagascar, the Seychelles, and the Comoro Islands. It also grows on Africa’s east coast, where Arab traders are thought to have introduced it. At 140 million years old, it is possibly one of the most ancient cycad species. The plants can reach heights of three to nine metres in nature, but tend to grow slower and remain smaller when planted in cultivated landscapes. The plant apparently contains carcinogenic alkaloids and a dangerous amino acid. Consistent consumption can lead to death, but, if properly prepared, the plant’s pith, seeds, and leaves are supposedly edible. Consumption is still not recommended. With blue-green, feathery leaves that can grow to up to 3 metres long, the Madagascar cycad makes for a wonderfully dramatic accent plant. It is named after Louis-Marie Aubert Petit-Thours, a French botanist who misidentified the plant as Cycas circinalis.
Michael Pascoe, NDP., ODH., CLT., MSc. (Plant Conservation)
"
| Family |
| Cycadaceae |
| Genus |
| Cycas |
| Species |
| thourasii |
| Category |
| Woody |
| Type |
| Tree (evergreen) |
| USDA Hardiness Zone |
| 9 - 11 |
| Canadian Hardiness Zone |
| Grow under glass |
| RHS Hardiness Zone |
| H1c - H4 |
| Temperature (°C) |
| (-10) - (-5) |
| Temperature (°F) |
| 14 - 23 |
| Height |
| 3 - 9 m |
| Spread |
| 0.5 - 3 m |
Photographs
Cultivars
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Description and Growing Information
Flowering Period
| General Description |
| Cycas thouarsii is a large, arborescent, palm-like tropical plant that grows in near-coastal forests and is known for its intense flushes of new leaves. It may produce offsets along its trunk. It is a dioecious plant. |
| Landscape |
| Cycads are commonly used as ornamental plants. Their rapidly increasing desirability as specimen plants is leading to issues of overharvesting, and many cycad species are now protected under local conservation laws. Young individuals make for interesting houseplants and larger specimens are impressive in conservatories and atriums. The plant is currently being researched as an industrial starch crop with possible uses in paper, solvents, and bioplastics. |
| Cultivation |
| Cycas thouarsii grows best in tropical environments. It grows well in direct sun in true tropical areas, but in less humid environments31 it thrives in bright, indirect light, partial light, or light shade. It needs a moist, well-draining soil. It can tolerate very light frosts over short durations but is prone to leaf scorching in such situations.The plant should be protected from long periods of serious cold. It should be mulched and watered during dry periods. |
| Shape |
| Very palm-like. This can grow to be a very tall plant. The cylindrical stem is monopodial and can grow to 9 m in height. The leaves can grow to 3 m in length, meaning the large crest of leaves that grows at the top of the tree can be as wide as 6 m across. |
| Growth |
| Fast |
| ID Characteristic |
| Cycas thouarsii’s new leaves are a distinct bluish colour when they emerge, and gradually change to a shiny, dark green as they age. The petioles and microsporophylls are spinescent. The seeds of Cycas thouarsii do not have a crested sclerotesta, distinguishing the species from several other cycads. |
| Pests |
| Most cycads are susceptible to several common pests. Mealybugs and scale insects (specifically the invasive Asian cycad scale and false oleander scale) are best treated by hand-picking and spraying with horticultural oil or insecticidal soap. Mild fungal sooty mold infections can be washed off the plant’s fronds. More severe infections will kill the plant. Root rot is common in cycads that are watered too heavily or were planted improperly. Crown rot and pink rot are also common to most palm-like plants. It is important to avoid “volcano mulching” and excessive pruning and to ensure that plants are watered near their base rather than from above. Cycad fronds may also turn yellow, which can be caused by over- or under-watering, mineral deficiencies, or simply age. In Australia there is a butterfly known as the Cycad Blue butterfly (Theclinesthes onycha), which will lay its eggs on cycad plants. The caterpillars feed on young cycad shoots and stems and will cause considerable damage to a plant. |
| Habitat |
| Cycas thouarsii grows in near-coastal environments, such as the forests behind beaches. It seems to prefer calcareous, coral-derived sands. The plants grow as individuals or in small groups. These areas receive an average of 1000 mm to 3000 mm of rain per year. Cycas thouarsii’s natural habitat is under threat from coastal developments and agricultural expansion. |
| Bark/Stem Description |
| Cycas thouarsii’s stem is tall, columnar, and generally unbranched, and it produces a large crown of fronds at its apex. These characteristics lead many to confuse it with a palm tree. This is the same characteristic stem seen in fossilized cycads. Many specimens begin to lean as they get taller; this is due a combination of the plant’s very heavy weight, its rather limited root system, and strong winds in its native environment. The stem is covered in brown leaf bases, which persist even after the leaf has fallen off the plant. These leaf bases are woody, thick, and rough, as serve as protection for the stem. The plant also produces brown scale leaves which persist alongside the leaf bases on the trunk. |
| Flower/Leaf Bud Description |
| The leaf and flower buds have not been the subject of much study in the past; as a result, descriptions are not available. However, it has been noted that the leaves are fern-like in how they unfurl, and show involute vernation. |
| Leaf Description |
| Cycas thouarsii’s leaves are very large and pinnately compound. The plant produces its leaves in large growth flushes, with up to 40 leaves emerging at once. The leaves may be up to 150 cm long and 30-60 cm wide. They are bluish when they emerge and darken to green as they age. The petioles are 40-50 cm in length. They are spinescent and glabrous. Each leaf has 60-100 pairs of leaflets, which can be 20-38 cm long and 8-12 mm wide. The leaflets are varying degrees of tomentose when they emerge but will shed the tomentum as they grow. |
| Flower Description |
| This plant is dioecious, meaning one plant will only bear either male or female reproductive structures. These structures grow as cones or inflorescences. Each consists of a central axis surrounded by spiralling megasporophylls (which bear ovules) or microsporophylls (which bear pollen sacs). The male cones have short peduncles, are pale orange-brown in colour, and are 30-45 cm long and 12-15 cm wide. The female inflorescences are very loosely structured and consist of many megasporophylls. These leaf-like structures are yellowish, tomentose, and grow to be 29-32 cm long. Each bears 2-6 glabrous ovules. |
| Fruit Description |
| The seeds are ovoid or globose. They are approximately 4 cm wide and 5-6 cm long. The sarcotesta (outer coat) is orange-red-brown. The sclerotesta is smooth. The seeds possess a spongy endocarp which may have evolved to help them float. |
| Colour Description |
| The large trunk is brown. The leaves are blue-green when they emerge and darken to a deep green with age. Cycas thouarsii, an evergreen plant, retains its green foliage throughout the year and does not possess any notable autumn colour. Reproductive structures are yellow or brown. |
| Texture Description |
| The plant is palm-like in appearance. The large crown of leaves appears soft and feathery. The evergreen foliage remains the same throughout the seasons. |
| Notable Specimens |
| Huntington Gardens: San Marino, California, United States of America, Fairchild Tropical Botanic Garden: Coral Gables, Florida, United States of America, Royal Botanic Gardens, Kew: London, United Kingdom, Masoala National Park: Northeast Madagascar, |
| Propagation |
| Cycads produce offsets (basal growths also called pups or suckers) as they mature. These growths can grow to full size if left alone, but they can also be propagated and grown into a caudex (a tree trunk with leaves that form only at the apex). To propagate a cycad using this method, follow these steps: 1. Fully expose the pup and remove all surrounding soil. 2. Use a sharp, sterilized knife to cut the pup away from the mother plant. Ensure that the cut is clean and smooth. 3. Check the pup for rot. It usually manifests as dark, squishy spots and can be cut away with a sharp, sterile tool. 4. Apply a fungicide to the cut surface(s). Alternatively, let the pup callous for 1-2 weeks. 5. Soak the pup in a liquid fungicide for 30 minutes. 6. Soak the pup in a liquid root stimulant for 30 minutes. For steps 5 and 6, watch to see if the pup floats. Floating usually indicates desiccation or severe central rot and the pup will probably not survive. 7. Apply agricultural tar or melting wax to the cut surface(s). This will prevent future rot. 8. Plant the pup in clean pumice, scoria, or coarse sand. These materials are all well-draining and will reduce the risk of rot. The pup should be planted just deep enough to keep it stable (generally about 1/3 of its height). 9. Wait until the pup produces roots and a flush of leaves. This can take anywhere from 6 months to 2 years. 10. Once the pup is well-established, transfer it to the ground or to a deep pot. Cycads can also be grown from seed. Seeds should be collected from external fruit, cleaned, and stored for several months to allow the inner embryo to fully develop. Germination can take 6-18 months. |
| Ethnobotanical Uses (Disclaimer) |
| Arab traders are believed to have introduced the Madagascar cycad to other regions, presumably for its food uses and visual appeal. However, the plant apparently contains dangerous alkaloids and amino acids. If the plant is not cooked properly, consumption can lead to nervous disorders or death. The nuts are very high in starch and are considered a famine food. Consumption is generally not recommended, however, due to the possible danger of poisoning. Cycads wood and leaves are traditionally used for building and thatch materials. |
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