Cycas circinalis: Structure and Function

The Queen Sago Palm is a gymnosperm, but not what you normally think of when you think of one. It is in the "Cycad" family, a unique group of plants which look very similar to palms, hence the common name of this species, but they significantly differ and are much more closely related to other gymnosperms such as pine trees.

Despite not being evolutionarily close to a palm tree, the Queen Sago Palm looks strikingly similar to one, with a long trunk which has long, stiff leaves branching out at the top. These leaves are arranged in a circle around the crown of the trunk and are considered "pinnate", meaning the leaves are composed of a central leaf stalk with many small leaflets emerging from either end. That means that a cycad does not have branches, and what look like branches are actually the leaf ribs and what look like leaves are actually leaflets! Also located on the top end of the trunk are the cones which this species uses to reproduce (rather than using flowers like angiosperms). 

Something unique about the Queen Sago and the Cycad family as a whole, is that although they reproduce via cones like other gymnosperms, they are considered "dioecious", which means that each individual cycad plant produces either male cones or female cones. This means that unlike pine trees, pollen must travel a significant distance for successful pollination, all the way to a second cycad plant rather than just to a different cone on the same plant. This means that cycads are one of the few gymnosperm families that rely on insects for pollination rather than the wind.

Additionally, the Queen Sago Palm, like most other cycads, is highly poisonous, with the seeds containing a potent neurotoxin. However, the seeds can also be used to make flour, and are commonly eaten by local inhabitants. This requires the seeds to be soaked 5 times to remove the poison, with even the water runnoff from the soaking being considered highly toxic. After this long process, the seeds can finally be ground up and used as a food source.

Lastly, these plants, like most species of cycads, are considered endangered and have been in decline all around the world. Cycad poaching is a common issue, as the unique look of these beautiful plants make them desired as garden or lawn decorations, but botanical gardens such as the one at UW-Madison work to keep this species alive for future generations.

Cycas circinalis: Evolutionary Relationships

Cycads have an extremely ancient evolutionary history, and have been described as the "dinosaurs" of the plant kingdom. The Queen Sago palm is one of the 331 remaining cycad species still existing, but they have previously dominated the land and appeared in the mid-Permian era (~270 million years ago). This is way before the diversification of angiosperms, which occurred between about 130 and 90 million years ago, and is so long ago that cycad distribution can be explained by continental drift as Pangea broke apart. The first major cycad diversification event occurred around 200 million years ago, leading to the Cycas branch, and no other cycad groups appeared for millions of years until the second (and most recent) diversification event only about 10 million years ago.

The absolute ancient nature of cycad evolution has led to some very interesting evolutionary phenomena. Something unique about cycads is their unique method of pollination, relying on various species of beetles rather than just wind like other gymnosperms. The earliest direct evidence of insects interacting with cycads comes from 100-million-year-old thrips encased in amber, which have been found bearing cycad pollen. How this interaction arose is a fascinating example of coevolution. Many gymnosperms secrete a "pollination droplet" from the cone which captures pollen on the outside and is then withdrawn, transporting the pollen to the ovaries and assisting pollination. These pollination droplets naturally contained sugars and proteins, which insects visited and consumed. Insects would visit cones which had a higher concentration of sugar in the pollination droplet, giving them a higher chance of being pollinated, giving them an advantage over wind-pollinated gymnosperms, allowing them to survive in areas where they normally wouldn't be able to. The Queen Sago Palm is the only gymnosperm in Sri Lanka, a tropical area with very little wind, due to this unique relationship. Cycad cones began act as a mating and brood site for insects due to the abundance of food within the cones. Although insect feeding and larvae deposited in the cone do damage ovules, this number is typically low enough to justify the extra boost in pollination.

What began as a random mutation providing some desirable nutrients on pollination drops turned into a catalyst of coevolution between beetles and cycads, developing an evolutionary relationship which explains the distribution of the Queen Sago Palm in relation to other gymnosperms, and is something which makes cycads a fascinating and unique group of plants.

Cycas circinalis: Ecology

Due to its extremely ancient history, the ecology surrounding the Queen Sago Palm has changed drastically over the species' lifespan. Cycads are found all around the world, seeming to have achieved an incredibly wide distribution which seems somewhat random. This can be explained by the abiotic conditions of Pangea, which had few natural barriers and a relatively uniform climate, allowing cycads to spread far across the continent. When Pangea split apart due to continental drift, cycads stayed rooted on the moving land as the Earth's surface shifted into what it is today. Continental drift subjected the cycads to new ecosystems, causing an extinction of cycad species. Currently, cycads are found in areas which share abiotic factors with Pangea, that being warm, wet areas near the tropics. 

Additionally, as other kinds of plants diversified, the cycad genus became outcompeted in many areas, causing their distribution to also be limited by biotic factors. Angiosperms, and even other kinds of gymnosperms compete with cycads for space, water, and soil nutrients, and are generally much more efficient in reproduction than cycads. Therefore, cycads are rare in areas with many other plant species, which explains the distribution of the Queen Sago Palm. Due to its unique pollination method, the Queen Sago Palm is able to reproduce well in environments where other plants would struggle, thriving on the tropical islands of Southeast Asia. A lack of wind in these environments limits the distribution of other gymnosperms, which allows the Queen Sago Palm to survive without significant competition within its own niche.

Unfortunately, due to the strong biotic and abiotic factors limiting its distribution, along with human poaching, the Queen Sago Palm is considered to be endangered. The Queen Sago Palm plays in important role in providing food, shelter, and reproductive grounds for many local insects, so its extinction would ripple across local ecosystems and cause profound negative effects. Additionally, this plant is prized for its appearance, and used as an ornamental plant in some private collections. Human poaching of cycads for the purpose of private collection is a major threat to this species due to their numbers in nature already being very limited, and therefore more anti-poaching regulations and protections should be placed on areas where these cycads are still found. If these steps are not taken, the Queen Sago Palm can be preserved in botanical gardens such as the one located at UW-Madison to prevent its total extinction, but these cycads must be legally and responsibly sourced. Raising awareness of and taking action against the poaching of cycads would give this species the best possible chance of continued survival, protecting the ecosystems which depend on it and preserving its natural beauty and intrigue.