Common Name:

General Information

Cycas siamensis is a slow-growing, deciduous, palm-like plant with an erect main stem that can eventually be around 100 - 150cm tall, though usually shorter; this is topped by a crown of erect to spreading leaves each around 80 - 100cm long[].
The plant is harvested from the wild for local use as a food and medicine. It is sometimes grown as an ornamental.
This species is widespread and locally extremely abundant. However, the population is estimated to have declined by more than 30% over the past 90 years based on extent of conversion to agriculture and due to collecting for the ornamental trade. The plant is classified as 'Vulnerable' in the IUCN Red List of Threatened Species(2013)[].

Known Hazards

We have no specific information for this species, but most if not all members of this genus are believed to contain toxins. The two main toxic compounds that have been identified are cycasin and macrozamin. When ingested in sufficient quantities, these compounds are extremely poisonous to humans and many other animals, and have been shown to cause liver damage and cancer. Cycasin and macrozamin have a cumulative effect upon the body and are suspected of causing neurological disorders when ingested in small amounts over long periods of time.
There is a long history of human use of this genus as a starch-rich food, but it should be noted that the plants needed to be treated in various ways in order to remove any toxic principles. Caution should be exercised even with properly prepared foods, since even then regular consumption may lead to severe health problems and death. Since many of these species are becoming increasingly rare in the wild, this is probably a food best left to times of food shortage when other, better foods, are not available[, ].

Botanical References

Range

Southeast Asia - Myanmar, Thailand, Cambodia, Laos, Vietnam.

Habitat

Dry forests on limestone hills[]. Full sun to light shade in low open woodland on flat country or low hills, often in dense stands. Woodland is often dominated by Dipterocarpus tuberculatus with associated trees such as Erythrina and Bombax[].

Properties

Conservation Status	Vulnerable
Edibility Rating
Medicinal Rating
Other Uses Rating
Habit	Deciduous Shrub
Height	1.50 m
Growth Rate	Slow
Pollinators	Insects
Self-fertile	No
Cultivation Status	Ornamental, Wild

Cultivation Details

A plant of tropical woodlands, growing in areas that are characteristically seasonally wet and dry with the monsoon weather patterns of the region, with particularly pronounced and extended dry periods[].
This species is found in the wild in limestone-based soil among limestone boulders[]. An almost universal requirement for cycads is a well-drained but moisture-retentive soil, and by far the best soils are sandy gravels and light loams which provide the required drainage and aeration necessary for good growth. Cycads will generally not grow well in clay soils unless those soils are heavily amended with sand and organic matter[]. A neutral soil (pH 7), is generally best for most species of cycads and allows the proper absorption of nutrients. A slightly acid soil is better for most cycads than a basic one[].
Unlike many species in the genus, this plant is completely deciduous, often being without leaves for some months (and often looking rather dead at this time), retaining the deciduous habit even in cultivation[].
Unlike most other members of the genus, this species does not transplant easily. The best time to try is just before the beginning of a new growing season, the roots being trimmed if they are damaged and perhaps some leaves being removed. New roots should develop quickly as the season progresses[].
Species in this genus form structures known as coralloid roots. These roots branch off from the taproot or secondary roots and are distinctive in that they grow laterally or upward, forming a nodular mass at the apex. These coralloid roots occur slightly below or slightly above the soil surface and generally contain cyanobacteria, also known as blue-green algae. These are able to fix atmospheric nitrogen and make it available as a nutrient to the plant. The ability to extract this important nutrient from the air explains how many cycad species are able to survive on almost sterile soils[].
A dioecious species, with individual plants producing either all male or all female cones. Therefore both male and female forms of the plant need to be grown if seed is required[]. On very rare occasions, usually when a plant has been under severe stress, it can change sex and produce either all female or all male cones[].

Edible Uses

Species in this genus are generally toxic unless the food is prepared correctly. See notes above on toxicity.

This species is said to have the same uses as Cycas rumphii. These uses are as follows:-
The pith is rich in carbohydrate and a sago can be made from it[, , , ]. This use will kill the plant[].

The raw seed is poisonous, but after being cut into thin slices, dried, then steeped in water for a few minutes and dried again, it becomes edible[, , , , ]. It can be used as a sago[, ]. Using the seed for food cannot be recommended, however. The globose to ovoid seeds of Cycas siamensis are 27 - 29mm long and 22 - 30mm in diameter[].

The very young leaves are edible[]. When around 30 - 40cm long, the young, not yet quite unfolded, succulent leaves are cooked and eaten as a vegetable[, ].

The plant yields a gum[, , ].

Medicinal

A gum obtained from the plant has been used medicinally, particularly as an agent that is said to produce rapid suppuration when applied to malignant ulcers. The gum also has the repute of being a good antidote for snake and insect bites[].

This species is said to have the same uses as Cycas rumphii. These uses are as follows:-
The pollen is narcotic[].

The bark and the seeds are ground to a paste with oil and used as a poultice on sores and swellings[].

The juice of tender leaves is useful in the treatment of flatulence and vomiting[].

Other Uses

A gum exudes through wounds in the plant, especially from the megasporophylls, stems and leaves[]. It is used medicinally and as an adhesive[].
When placed in water, Cycas gum begins to swell almost immediately. By the end of several days, it expands to many times its original size and becomes so colourless and transparent that it cannot be seen in water but must be felt for with a rod[]. Cycas gum has been likened in its properties to that of Sterculia setigera[]

This species is said to have the same uses as Cycas rumphii. These uses are as follows:-
The bark sap is used as a glue[].

The fruits are strung together to make children's toys or rattles[].

Propagation

Seed - best sown in containers as soon as it is ripe. Stored seed should be pre-soaked for 24 hours in warm water prior to sowing. The seed should be sown 2cm deep in individual pots, which are then sealed in plastic bags to keep them moist until germination takes place. Germinates in 1 - 3 months at 25°c[].
Division of suckers in the spring[].

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