A Pair of Cycads Aim to Reproduce in the UK for the First Time in 120 Million Years

Photo by Danorton licensed by CC BY-SA 4.0

We tend to speak in the future tense when it comes to climate change. Phrases like "climate change will alter..." and "species will be affected by climate change..." suggest that these are issues we will eventually face at some point down the road. In reality, climate change is happening and life is already responding. Plants are some of the best indicators that thing are and have been changing since humans started wreaking havoc on natural systems.

Even in the most remote corners of our planet, where human presence is almost nil, we are finding evidence of climate change in the flora. For instance, deep in the Andes Mountains, trees are already adjusting their ranges to cope with changes in regional climate. And now, cycads are reproducing outdoors in the UK for the first time since dinosaurs walked the Earth.

Sago palms (Cycas revoluta) are native to parts of southern Japan and though they can handle frosts, they require mild winters and hot summers to successfully reproduce. A few decades ago, one would have a hard time trying to overwinter these cycads outdoors in the UK but the climate has been changing. Today, these plants can be successfully grown outdoors in the southern portion of the country provided they are given a little bit of shelter. Though they will grow well in such situations, convincing these plants to reproduce is another matter entirely.

The UK is no stranger to the effects of climate change. For instance, the plants in question are growing in the Ventnor Botanic Garden on the Isle of Wight where even today’s lowest temperatures are significantly hotter than even the hottest recorded temperatures on the island 100 years ago. The plants are responding accordingly.

For the first time in UK’s human history, both male and female sago palm cycads are producing cones at the same time outdoors. This means that cycads will be able to successfully reproduce at this latitude since at least the Cretaceous Period, roughly 120 million years ago. During the Cretaceous, distant cousins of these cycads could be found growing in what today is the UK. At that time, Earth’s atmosphere was chock full of CO2 and quite hot. The fact that cycads are once again able to reproduce in the UK is alarming to say the least. It is a forecast of more changes to come.

UPDATE: Thanks to Dr. Susannah Lyndon and Robbie Blackhall-Miles for bringing to my attention that this is actually not this first time this has happened in the UK. Apparently Sago palm cycads have produced cones in places like London in recent history. Nonetheless, such events are evidence of a warming climate.

Photo Credits: [1] [2]

Further Reading: [1] [2]

Gymnosperms and Fleshy "Fruits"

Fleshy red aril surrounding the seeds of Taxus baccata. Photo by Frank Vincentz licensed under the GNU Free Documentation License.

Many of us were taught in school that one of the key distinguishing features between gymnosperms and angiosperms is the production of fruit. Fruit, by definition, is a structure formed from the ovary of a flowering plant. Gymnosperms, on the other hand, do not enclose their ovules in ovaries. Instead, their unfertilized ovules are exposed (to one degree or another) to the environment. The word “gymnosperm” reflects this as it is Greek for “naked seed.” However, as is the case with all things biological, there are exceptions to nearly every rule. There are gymnosperms on this planet that produce structures that function quite similar to fruits.

Internal anatomy of a Ginkgo ovule with red arrow showing the integument.

Photo copyright Bruce Kirchoff, Licensed under CC BY 2.0

The key to understanding this evolutionary convergence lies in understanding the benefits of fruits in the first place. Fruits are all about packing seeds into structures that appeal to the palates of various types of animals who then eat said fruits. Once consumed, the animals digest the fruity bits and will often deposit the seeds elsewhere in their feces. Propagule dispersal is key to the success of plants as it allows them to not only to complete their reproductive cycle but also conquer new territory in the process. With a basic introduction out of the way, let’s get back to gymnosperms.

“Fruits” of Cephalotaxus fortunei (Cephalotaxaceae)

There are 4 major gymnosperm lineages on this planet - the Ginkgo, cycads, gnetophytes, and conifers. Each one of these groups contains members that produce fleshy structures around their seeds. However, their “fruits” do not all develop in the same way. The most remarkable thing to me is that, from a developmental standpoint, each lineage has evolved its own pathway for “fruit” production.

Ginkgo “fruits” are full of butyric acid and smell like rotting butter or vomit. Photo by H. Zell licensed under CC BY-SA 3.0

For instance, consider ginkgos and cycads. Both of these groups can trace their evolutionary history back to the early Permian, some 270 - 280 million years ago, long before flowering plants came onto the scene. Both surround their developing seed with a layer of protective tissue called the integument. As the seed develops, the integument swells and becomes quite fleshy. In the case of Ginkgo, the integument is rich in a compound called butyric acid, which give them their characteristic rotten butter smell. No one can say for sure who this nasty odor originally evolved to attract but it likely has something to do with seed dispersal. Modern day carnivores seem to be especially fond of Ginkgo “fruits,” which would suggest that some bygone carnivore may have been the main seed disperser for these trees.

“Fruits” contained within the female cone of a cycad (Lepidozamia peroffskyana). Photo by Tony Rodd licensed under CC BY-NC-SA 2.0

The Gnetophytes are represented by three extant lineages (Gnetaceae, Welwitschiaceae, and Ephedraceae), but only two of them - Gnetaceae and Ephedraceae - produce fruit-like structures. As if the overall appearance of the various Gnetum species didn’t make you question your assumptions of what a gymnosperm should look like, its seeds certainly will. They are downright berry-like!

Berry-like seeds of Gnetum gnemon. Photo by gbohne licensed under CC BY-SA 2.0

The formation of the fruit-like structure surrounding each seed can be traced back to tiny bracts at the base of the ovule. After fertilization, these bracts grow up and around the seed and swell to become red and fleshy. As you can imagine, Gnetum “fruits” are a real hit with animals. In the case of some Ephedra, the “fruit” is also derived from much larger bracts that surround the ovule. These bracts are more leaf-like at the start than those of their Gnetum cousins but their development and function is much the same.

Red, fleshy bracts of Ephedra distachya. Photo by Le.Loup.Gris licensed under CC BY-SA 3.0

Whereas we usually think of woody cones when we think of conifers, there are many species within this lineage that also have converged on fleshy structures surrounding their seeds. Probably the most famous and widely recognized example of this can be seen in the yews (Taxus spp.). Ovules are presented singly and each is subtended by a small stalk called a peduncle. Once fertilized, a group of cells on the peduncle begin to grow and differentiate. They gradually swell and engulf the seed, forming a bright red, fleshy structure called an “aril.” Arils are magnificent seed dispersal devices as birds absolutely relish them. The seed within is quite toxic so it usually escapes the process unharmed and with any luck is deposited far away from the parent plant.

The berry-like cones of Juniperus communis. Photo by Piero Amorati, ICCroce - Casalecchio di Reno, Bugwood.org licensed under Creative Commons Attribution 3.0 License.

Another great example of fleshy conifer “fruits” can be seen in the junipers (Juniperus spp.). Unlike the other gymnosperms mentioned here, the junipers do produce cones. However, unlike pine cones, the scales of juniper cones do not open to release the seeds inside. Instead, they swell shut and each scale becomes quite fleshy. Juniper cones aren’t red like we have seen in other lineages but they certainly garnish the attention of many a small animal looking for food.

I have only begun to scratch the surface of the fruit-like structures in gymnosperms. There is plenty of literary fodder out there for those of you who love to read about developmental biology and evolution. It is a fascinating world to uncover. More importantly, I think the fleshy “fruits” of the various gymnosperm lineages stand as a testament to the power of natural selection as a driving force for evolution on our planet. It is amazing that such distantly related plants have converged on similar seed dispersal mechanisms by so many different means.

Photo Credits: [1] [2] [3] [4] [5] [6] [7] [8]

Further Reading: [1] [2] [3] [4] [5] [6] [7]

A North American Cycad and its Butterfly

Photo by andy_king50 licensed under CC BY-SA 3.0

Most of us here in North America probably know cycads mainly from those encountered in botanical gardens or as the occasional houseplant. However, if you want to see a cycad growing in the wild, you don't have to leave North America to do so. One must only travel to parts of Georgia and Florida where the coontie can be found growing in well drained sandy soils. 

Known scientifically as Zamia integrifolia, the coontie is a cycad on a small scale. Plants are either male or female and both are needed for viable seed production. Here in the United States, the coontie is considered near threatened. Decades of habitat destruction and poaching have caused serious declines in wild populations. This has come at a great cost to at least one other organism as well.

Photo by James St. John licensed under CC BY 2.0

Thought to be extinct for over 20 years, a butterfly known as the atala (Eumaeus atala) require this lovely little cycad to complete their lifecycle. The coontie produces a toxin known as "cycasin" and, just as monarchs become rather distasteful to predators by feeding on milkweeds during their larval stage, so too do the larvae of the atala. The brightly contrasting colors of both the caterpillars and the adults let potential predators know that messing with them isn't going to be a pleasant experience. The reason for its decline in the wild is due to the loss of the coontie. 

Rediscovered only recently, populations of this lovely butterfly are starting to rebound. Caterpillars of the atala are voracious eaters and a small group of them can quickly strip a coontie of its foliage. For this reason, large populations of coontie are needed to support a viable breeding population of the atala. The coontie is becoming a popular choice for landscaping, especially in suburban areas of southeastern Florida, which is good news for the atala. As more and more people plant coonties on their property, more and more caterpillars are finding food to eat. This just goes to show you the benefits of planting natives!

An atala caterpillar and chrysalis. Photo by Monica R. licensed under CC BY 2.0

Further Reading: [1] [2] [3]