Cycads and their Golden Age

Joseph Brider, Natural Heritage Trust.
First published online (19 Feb 2021).

Japanese Sago-palm with male reproductive structure in top insert and female structures in bottom insert. Photo: CINHT

What do Japanese Sago-palms, Queen Sago-palms and Cardboard Palms all have in common? Well… they are NOT palms, they are all Cycads! The ‘palm’ reference comes from the shape of their leaves and cylindrical trunks but these plants are not even closely related to palms!

These recently introduced plants to the Cook Islands represent a very, very old lineage of plants that predate the dinosaurs.  These are very slow-growing, long lived plants with some specimens in the wild being over 1000 years old¹. A particular specimen of Cycad in Kew Gardens in the UK arrived at their botanical garden in 1775, making it 246 years old in 2021. Consequently, it also holds the record for being the oldest potted plant in the world².

Let’s dive in and learn about the charismatic, but often misunderstood plants.

Age of Cycads

Cycads are an ancient group of seed plants that evolved 280 million years ago³, 180 million years before the first palm evolved⁴. Cycads reached their prime during the Mesozoic period – especially the Jurassic period – so paleobotanists often refer to this period as the Age of Cycads. This period was also the time when Dinosaurs ruled the Earth, so zoologists refer to the period as the Age of Dinosaurs. Not surprisingly, many museum drawings, depictions and dioramas of dinosaurs often show cycads as the main plant in the landscape. Cycad fossils have been found on every continent, including Antarctica and at their height, they accounted for 20% of all plants on Earth. It is likely that Cycads were an important food source for plant-eating dinosaurs⁵.

Being such early pioneers, Cycad invented fundamental relationships with other organisms that lay the foundations for the evolution of many plants today; these include: symbiosis, pollination and seed dispersal. It is also possible that the evolution of poisonous leaves and fruit to protect from predators and grazers could have first evolved in Cycads!⁶

Cycads are no longer a dominant plant group on Earth today, flowering plants now hold that title, but their glossy leaves and regal stature continue to make them a common sight in gardens around the world.

What is a Cycad?

Cycads typically have a stout, woody trunk, known as a Caudex, with a crown of large, hard and stiff, evergreen leaves which resemble fern or palm leaves. All cycads are dioecious, meaning that a plant is either a male or a female plant, never both sexes on one plant. Cycads belong to a group of plants known as gymnosperms that includes Conifers, Ginkgo and Gnetales, all of these plants produce unfertilised seeds that are open to the air to be directly fertilised, as opposed to flowering plants that have an unfertilised seed encased in an ovary within a flower.

Female leafy scale with fertilised seed and unfertilised ovules of Queen Sago-palm. Photo: CINHT

Cycads produce a cone-like structure known as a Strobilus, this is a reproductive structure and it is with this, that we can distinguish between male and female plants. Male plants produce a slender, elongated spore strobilus made up of many cone scales that produce yellow pollen, whereas a female produces a larger, egg-shaped, leafy seed strobilus which will open up to reveal leafy scales with 2 – 8 small, seeds along its edge (see image at top of article). Wind and beetles are responsible for pollination in Cycads, where spores from male plants are transported to the unfertilised seeds (ovules) on female plants. Cycads produce unique Coralloid Roots, these are a specialised form of root, that look like a piece of coral attached to the main root, that forms a symbiotic mutually beneficial relationship with Cyanobacteria, where the plant produces food for the bacteria and the bacteria provides nitrogen for the plant⁷.

Cycads contain toxic components and care should be taken not to ingest any part of the plant. Although Cycads can make up a part of the medicinal and edible folklore of the people from where the plant is native, preparation requires specialist handling. Any attempt to utilise the plant for medicine or consumption should be avoided unless specially trained.

Cook Island Cycads

The Cook Islands Biodiversity and Ethnobiology Database records four different species of Cycad in the Cook Islands, all of which have been introduced in recent times.

Japanese Sago-palm (Cycas revoluta) – native to the China – Japan region, today it is widely planted around the world and is a commonly found Cycad in the Cook Islands. Being a member of the Genus Cycas, these plants have a single midrib running down the center of each leaflet. They are distinguished from our other Cycas species, the Queen Sago-palm by having a generally smaller leaf frond size (±1m) and leaflet length (±10cm) with stiffer, keeled, rigid leaflets, sometimes with a spiny tip.

An edible starch (Sago) is extracted from the plant but due to the toxins in the plant, the extract must be carefully washed to leach out the poisons⁸.

Queen Sago-palm with female strobilus. Photo: CINHT

Queen Sago-palm (Cycas seemannii) – native to New Caledonia, Vanuatu, Fiji and Tonga. This is a commonly planted Cycad in the Cook Islands, this species has a single midrib running the length of each leaflet. The fronds are around 2m long, leaflets are flattened (not keeled) and between 17-30cm long but not rigid. The orange to brown male strobilus is spindle-shaped (wide in the middle and tapering to the tips) and between 35-50cm long and can resemble an elongated, fleshy pine-cone when mature. The female strobilus is an oval compaction of leafy structures called Megasporophylls that contain ovules (unfertilsed seeds) along its margin. Oval seeds are only found on female plants, they grow to about 60mm and ripen to an orange-brown colour^9101112. Known as Namele in Vanuatu, it is a culturally important plant and a pair of Namele leaves features on the national flag of Vanuatu and their coat of arms. Additionally, in Vanuatu culture, the leaves are used to indicate a taboo or restriction – a pair of crossed leaves over a door or entryway indicates that one should not enter, Namele leaves tied around another tree indicates that someone claims ownership of that tree and its fruit¹³  and Namele leaves are used show whether a fishing ground is under customary protection¹⁴¹⁵, much like kikau is used to show areas under Raui in the Cook Islands.

Queensland Lepidozamia fronds with male strobilus. Photo: CINHT

Queensland Lepidozamia (Lepidozamia hopei) – originally only found in Queensland, Australia, the horticultural trade has spread this plant to many parts of the world. An odd Cycad in the Cook Islands, with only one individual plant known on Rarotonga. Often unbranching, this species has the record for the tallest Cycad species on the planet today, attaining a height in excess of 15m. The leaflets are distinguished from Cycas by the absence of a midrib on the leaflets, this species has numerous (15-25) veins running parallel, down the length of the  leaflet. The male strobilus is cylindrical and between 25-40cm long. The female strobilus is oval and much longer with greater girth. The large red seeds are 4-7cm long¹⁶.

Australian Aboriginals are known to eat the seed of this plant, although preparation does require specialised knowledge. Some older, taller trees in the Australian forest show footholds on their trunks, cut by Aboriginal gatherers who collected the seeds¹⁷.

Cardboard Palm fronds with male strobilus. Photo: CINHT

Cardboard Palm (Zamia furfuracea) – native to Mexico, this plant is becoming a common feature of gardens in the Cook Islands. Its leaflets are distinctively different from our other Cycads, in the sense that they are pale-green, oblong with pointed tips, thick and leathery and sometimes covered with fine short hairs, whereas the other species have narrow leaflets. The leaf form tends to be quite loose as opposed to the densely packed leaves in our other Cycads.  The Latin name ‘furfuracea’ is a reference to the hairy nature of the leaflets, which can also make them feel like cardboard, hence the common name Cardboard Palm. The caudex trunk is often underground or just breaking above the surface if planted on flat land or in a pot. The strobilus of either gender is cylindrical with a pointed tip but male plants have a shorter strobilus and several often sprout at one time, whereas female strobilus are much larger and limited to one strobilus at a time. The seeds are red and about 1cm long¹⁸. Reproduction is primarily through seeds (not suckers) but is extremely difficult in cultivation, this has led to many plants being collected illegally in the wild, leading to the species being classified as Endangered by the IUCN in 2009¹⁹.

Cycads are truly wonderful plants, timeless relics that have seen eons of evolution, they persist today as example of how steadfast life on our planet can be.

Citation

Brider, Joseph (2021) Cycads and their Golden Age. Cook Islands Natural Heritage Trust. https://cinature.org/2021/02/19/cycads-and-their-golden-age/

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