Monday, January 10, 2011

The Cycad Chronicles, Part 1: Prehistory

Behold, the cycad.
Encephalartos villosus in Desert House of ABG. Photo: Hilary Hart.
That's right, this is not a fern but a cycad.  These plants vary in size from towering trees to ground-hugging shrubs.  Their leaves can be delicate and feathery and also thick, tough, and cruelly armed.  In fact, my first formal introduction to a cycad began this way:  “Watch out for that one.  It’s a real bastard.”  In this case, Conservatory Manager Paul Blackmore was referring to a rather spectacular specimen of Encephalartos horridus in the Desert House.  It’s not a plant you want to brush up against.  Its dense, entangled foliage is lined with wicked spines. Horridus indeed.
Encephalartos horridus. An embrace to be avoided. Photo: Hilary Hart
Most cycads, however, are content to greet the world sans piercing spines. While they often resemble palms or ferns, cycads are related to neither.  In his foreword to David L. Jones’ important work Cycads of the World, botanist Dennis Wm. Stevenson laments this confusion while expressing gratitude to “the native people who always know where to find” cycads in the wild. “And without taking one to palms!”  Indeed, a number of cycad species develop palm-like crowns atop tall stems that resemble enormous trunks.
Cycas angulata near Borroloola, Austrialia. Photo: Len Butt of PASCOA.
Cycad Madness
I was unaware of cycads until volunteering at ABG.  When I thought I’d bone up on the plant, I had no idea I was flirting with obsession.  The signs, however, were soon apparent: The piles of printed journal articles, the unswerving cycad monologue, the caressing of sago palms in Home Depot.  “Did you know they’re really cycads, Cycas revoluta?” I heard myself asking uninterested shoppers.  
Sago palm aka Cycas revoluta available at Lowe's or Home Depot.
It was Mike Wenzel who gave me the clue that my new-found passion was trite, at least among floraphiles.  It happened while Julia Rittenhouse (Conservatory Horticulturalist) was repotting cycads for a display in the Tropical Rotunda.  Mike stopped by and casually asked Julia:
“Are you mad for cycads yet?”
“No,” Julia replied. “Just mad from being poked all over.” 
That took me down with a bump.  This exchange taught me two things: Cycads commonly ensnare the susceptible, and not everyone is susceptible.  Not really a problem, except when it comes to writing about cycads.  In my state of cycad enchantment, how can I discern what will interest the unafflicted, when everything about them fascinates me?  Perhaps now you can understand why it has taken me so long to publish this floraphile entry.

Cycads are very, very old.  They were here before humans, before dinosaurs, and before most of the plants that are common today.  While they now grow in pockets in the tropics and in subtropical regions, cycads once were everywhere on the globe.  And because they were so populous, cycads have left a comparatively prolific record of themselves in fossil form.  These fossil cycads in turn allow us to imagine what the world once looked like and theorize about how it has evolved. 
Here’s an example of a cycad fossil, actually the best example of a cycad fossil because it is the whole plant including a male cone.

Megafossil of whole plant cycad. Collected in 2009 from the Yangcaogou Formation (Upper Triassic) in Changheying, Beipiao, Liaoning. Related to living Zamiacea.
As you can imagine, plants are quite a bit more fragile than bone, so they tend to fall to pieces more easily.  Such a large intact fossil is thus far unique.  Moreover, this fossil is from the Late Triassic, which means the plant was alive 200-250 million years ago.  Many of the first dinosaurs evolved during the Late Triassic.  And, while the fossil was discovered in what is now China, Asia was still part of the undifferentiated supercontinent Pangaea when the living plant first broke ground and lifted its leaves skyward.
Meyers Konversationslexikon, a German encyclopedia, 4th edition (1885-1890) Plate title: "Life restaurations of some Triassic plants." 

The Age of Dinosaurs/The Age of Cycads
As a species, cycads reached their hey day around the 150 million years ago, during the Jurassic Period.  And as any grade-schooler will tell you, this is the Age of the Dinosaur, the glory days between extinction events.  Consequently, many refer to the Age of the Dinosaurs as the Age of the Cycads (although I don’t think this nomenclature is really going to catch on with the kids).  Dinosaur and cycad fossils have been found together.  Moreoever, if you have ever wondered what dinosaurs ate, you can be nearly certain that cycads were on the menu.  Hence, any Jurassic diorama worth its salt should include cycads.
To solidify the connection between dinosaurs and cycads, here is a National Park Service poster:

Where is this wonderful Fossil Cycad National Monument?  It was in the Black Hills of South Dakota from 1922-1957.  Alas and alack, it is no more.  But for mismanagement, we might have had a National Park dedicated to cycads with in situ specimens.  This loss seems especially poignant to me because the South Dakota landscape out of which these fossilized tropical plants are retrieved brings home how vastly different the world once was in a way that no museum diorama or artistic rendering can.  The latter might as well be depictions of other planets.  To see a fossil in situ would give the intervening eons dimension. And the living cycad, with its striking resemblance to fossilized cycad remains, animates the continuity between the prehistoric world and now.
Paleobotanist George Reber Wieland supervising a CCC crew during the 1935 fossil cycad test excavation (Yale University).

A World Before Flowers
Now if we are to have an accurate Jurassic diorama of the mind, we should probably consider some other flora.  When the cycads were at their most flourishing, around 150 million years ago, the climate was warm and moist with just a few arid spots.  As a result the world grew luxuriant with vegetation from pole to pole. (In fact, one reason that the climate is thought to have been almost uniformly tropical is because cycad fossils have been found in both Greenland and Antarctica.)  Also in abundance were other gymnosperms: ginkgoes, and conifers, including close relatives of living species of redwoods, cypresses, pines, and yews.  Cycads were dominant, that is until the late Cretaceous Period, when a new group of plants emerged, the angiosperms, otherwise known as flowering plants. 
These showy upstarts had a number of advantages over cycads and the other gymnosperms: They grew faster, matured sooner, and because their seeds are pollinated in an enclosed in an ovary they could survive broader dispersal. (The term “angiosperm means “enclosed seed while “gymnosperm” comes from the Greek word for “naked seed.”) Flowering plants very quickly eclipsed the gymnosperms.  Where once much grew but nothing bloomed, today flowering plants make up about 95% of all land plants. 
So if your Jurassic imaginarium features the gentle brontosaurus feeding on a gigantic blossom, please revise.

More likely.  Artist: Karen Carr.

Surviving to the Present
If the angiosperm overthrow weren’t enough, cycads were also up against continental drift and glaciation. As the theory goes, around 180 million years ago, the supercontinent Pangaea split into Gondwana in the south and Laurasia to the north.  Laurasia, though changed in shape, remained intact except for North America. Whereas, Gondwana broke apart into the landmasses that appear today’s maps as Australia, Africa, South America, Antarctica, India, New Guinea and New Zealand.  Continental drift is slow enough to accommodate adaptation, but the turn in the weather during the Pleistocene Period caught a lot of flora and fauna by surprise.  The rapid advance of glaciers carried off a lot of megafauna, including mammoths, mastodons, saber-toothed cats, and the Neanderthals. Where the glaciers made their bid for lebensraum, you will not find living cycads, only fossils.  Consequently, cycad distribution today looks like this:  

Cycads generally occur between the Tropics of Cancer and Capricorn, or between 30 degrees north latitude and 35 degrees south latitude.
Calling the cycad a "living fossil" suggests that the plant has changed very little from the versions of itself that lived millions of years ago.  And this is true of some of the species of cycads.  Those that continue to live in the warm humid conditions that prevailed in the Jurassic and Early Cretaceous Periods, like the Cycas revoluta I visit at Home Depot, are considered more primitive. In fact, compare the complete fossil from the Triassic to the Home Depot sago palm. Similar, no?

But many species of cycads have adapted to live in very different climes. The Encephalartos species that grow in the xeric Cape region of South Africa, like my horridus friend in the Desert House, are truly the tough cookies of the genus.  They have adapted to a hard-scrabble life by soaking up and storing water when it does fall, and growing spines to fend off the predations of animals that would like very much to feast on them.
Had cycads remained truly unchanged they would never have survived.  They would have gone the way of the dinosaurs or much of the North American megafauna of the Pleistocene: extinct despite their charisma. 
Finally, part of what draws me to the cycad is that to learn its story is to learn the story of the planet. And I fit into that story too.  Humans may have arrived late on the scene, but we have evolved alongside the cycad to survive to the present not as artifacts, but as living creatures. 
The greatest delight which the fields and woods minister, is the suggestion of an occult relation between man and the vegetable.  I am not alone and unacknowledged.  They nod to me and I to them.  The waving of the boughs in the storm, is new to me and old.  
-- Ralph Waldo Emerson from his essay Nature.