At the end of the Carboniferous Period, radical changes occurred on the planet. Approximately 335 million years ago, the continents merged into one supercontinent which we call Pangaea. The climate changed from very humid and warm to “continental”—characterized by cold winters and hot summers. Think the Great Plains with triple-digit hot summers and frigid winters.
The plate tectonics that created Pangaea gradually broke it apart 175 million years ago. During its existence the first seed-bearing plants appeared.
Seeds are a much more efficient way to reproduce than spores. A seed contains the plant embryo as well as nutrients needed by the sprout to get a good start in life. The seed coat ensures the embryo survives cold and dry spells.
Cycads, primitive seed-producing plants, evolved around the same time as the first dinosaurs. Cycads are the intermediate evolutionary step between ferns and conifers. (An article about conifers is on page 6 of the garden column archives, accessible by clicking on Columns in the navigator above.)
We may link the Jurassic with dinosaurs but botanists call it the “Age of Cycads.” Cycads were the dominant plants until the emergence of flowering plants about 135 million years ago. Today there are 280 species found in Australia, Japan, Southeast Asia, Africa and the Americas. Unfortunately, they are threatened by habitat loss as well as over-zealous plant hunting.
Cycads are dioecious, meaning there are male and female plants. The seeds are produced on cones (see photo below). Male plants have pollen-bearing cones and females produce the seeds. In nature cycads are pollinated by the wind or weevils that are attracted to the odor of ripe pollen.
Young cycads have lacy, fernlike foliage and age into something resembling palms. (Palms are flowering plants completely unrelated to cycads.) They grow very slowly, producing one ring of new foliage each year, and are very long lived.
Botanical gardens are vital to the survival of these ancient plants. The Amsterdam Hortus Botanicus was given a male cycad from South Africa. It is the only known specimen of this species. It does produce offsets which are all male that the garden shares with other botanical gardens in an effort to preserve the species.
Even when both male and female cycads are in the same bot garden, they do not always produce cones at the same time. Staff collect and save pollen to fertilize the eggs and then nurture them to share with other gardens.
One of the best cycad collections in the world is in the botanical gardens of The Huntington Library in San Marino, California. The mild climate allows the collection of more than 1500 cycads to be planted outside rather than in a greenhouse. This allows the visitor to imagine what the Jurassic World may have looked like, though genetic research has revealed that modern cycads evolved only 12 million years ago.
Those with a taste for the exotic may be wondering if cycads are available to home gardeners. The answer is yes. There are quite a few online sources for both plants and seeds. The most popular cycad in the world is the Sago Palm. Others commonly available are the Mexican native Dioon edule and Florida Coontie. Both are cold tolerant to Zone 8.
Master gardener Ann Bartlett lavishes attention on the ornamental beds surrounding her home when she is not on safari through prehistory plant-hunting for the edification of her readers. This winds up her series about primitive plants. For earlier installments, click Columns in the navigator above or the Bartlett on Gardening icon on The Planet's homepage.