- Category: General Information
Cycads, along with palms, tree ferns, cordylines, bromeliads and many other foliage plants, are very popular subjects for cultivation. Although other groups of plants attract their own groups of dedicated disciples, the attention paid to cycads is well out of proportion to the number of species of cycad found in the world.
Cycads are very popular plants with the dedicated collector and cycad enthusiasts will go to extraordinary lengths to obtain new plants. Rare species and specimen plants are expensive, so large collections represent a considerable outlay in time and money. A wide range of species are propagated by specialist nurseries and new species and variants are constantly being introduced into cultivation.
Cycads are excellent horticultural subjects and are of value to groups other than collectors. Landscapers find their primitive shapes and silhouettes appealing and their predictable dimensions extremely useful. Many species make very decorative container plants and are excellent for indoor use where there is sufficient light. As a bonsai subject, cycads are only rivalled by their gymnosperm relatives.
It behooves all cycad enthusiasts to take an active role in the conservation of these unique plants. The regular propagation of seedlings from cultivated plants is one easy way in which growers can contribute.
History and Pre History of Cycads
The modern cycads are but a fraction of their ancestors (both in total numbers and in diversity of species), which reached their peak in the Jurassic and Early Cretaceous Periods, dominating the vegetation of the day. That the living species share characters with these early plants is obvious from an examination of fossils. It is tempting to speculate that these plants have survived more than 200 million years of evolution with very little change.
The long history of these plants tends to place in people’s ;minds the idea that cycads are now static and are incapable of evolving to meet environmental change. This is quite erroneous as the modern cycads are diverse and have successfully occupied a wide range of habitats, including littoral zones, grasslands, rainforests, deciduous mesophyll forests, evergreen sclerophyll forests, gorges, relict situations on ancients escarpments and even mangrove swamps. There is evidence that cycads have actively occupied recent available niches in the environment and their ability to adapt is supported by modern taxonomic studies into a wide range of genera. Thus these remarkable plants are obviously still evolving and are capable of responding to new environmental conditions.
Cycads are paradoxical in that they have obviously retained some primitive features *e.g. the presence of motile sperm cells), and yet have other characteristics which could be considered advanced. The apparent reliance of a large number of species of cycads on close relationships with insects to achieve pollination is extremely interesting and perhaps challenges the views of the primitiveness of these plants. Certainly these relationships are with ancient groups of insects but they represent a major evolutionary advance over using fickle physical systems such as the wind to achieve the same purpose. The success of such pollination systems must have contributed greatly to the survival of these plants over the ages and has more than likely aided their adaptation in modern habitats.
Cycads, then, are survivors from the past, but they now face the very real threat imposed by modern humankind’s greed.
Cycad-like-plants - and perhaps even true cycads - seem to have arisen some time in the early Permian Period, possibly about 230 million years ago. Certain fossils which have been classified as being related to cycads have been dated even earlier than this, from deposits laid down in the Carboniferous Period, but recent studies have suggested that these may in fact not be true cycads or even cycad relatives. The Permian Period lasted for about 41 million years and was the last epoch in the Palaezoic or Ancient Era, during which plants first became established on the earth. Whether cycads arose from the particular plant group, is unclear, but current opinion links them with the pteridosperms.
Cycads reached their peak of development and diversity in the Mesozoic or Median Era. They seem to have survived the transition from the Permian Period to the Triassic Period without apparent change and then became a well-established component of the world’s flora. Examples of cycad fossils in Mesozoic rocks have been found in Alaska, Antarctica, Australia, Europe, Greenland, India, North America, South Africa and the United Kingdom. During the Jurassic Period and until the middle of the Cretaceous Period, the world’s climate was warm to hot, with an abundance of moisture, and as a result plant growth thrived in these conditions. Plants, including cycads, grew luxuriantly at both poles of the earth, for the prevailing climate in these regions was warm. The Jurassic Period was the age of the dinosaurs and it was also the period when cycads achieved their pinnacle of abundance and diversity. It spanned 64 million years and occurred between 208 million and 144 million years ago.
The period which followed the Jurassic is known as the Cretaceous and this was the time of change for cycads and many other plants. During this period a newcomer arrived on the scene, the plant group known as the angiosperms, or flowering plants. These plants were faster growing and quicker maturing than the prevailing gymnosperms (which had possibly reached their zenith and were on the decline anyway) and they quickly diversified and expanded into all of the significant plant habitats. No major plant groups in existence at the time because extinct but all, including the cycads, declined in significance. The angiosperms thrived and because of their major adaptive feature – the enclosure of their seeds in an ovary – they were able to exploit all available environmental niches and are still the dominant plant group today.
(Extract from CYCADS OF THE WORLD by David L. Jones)