How do cycads reproduce?

Cycads

Cycads are a group of gymnosperm trees and shrubs. They are woody, seed producing plants with no flowers or fruit. Cycads often look similar to palm trees with branchless stems and a crown of leave at the top of the tree, but they are not at all closely related to palm trees.

They form the sub-class Cycadidae which belong to the class Pinopsida and includes all the gymnosperms plants. The cycads are widely distributed around the world but are mostly found in tropical areas. Many species are threatened with extinction due to habitat loss.

Cycad Growth form

Cycad plants grow as trees and shrubs. They typically have short trunks topped off with a green crown of large compound leaves. In appearance they closely resemble palm trees, however, they are not closely related.

Most species do not grow more than a few meter tall. Hope’s cycad of Australia is one of the tallest species and is known to reach 20 m (65 ft.) in height. More primitive cycads were often much taller than the majority of cycad species that currently exist.

Stems are usually unbranched and fallen leaves of the past leave leaf scars that encircle the stem. Internally, stems are mostly made up of soft storage tissue rather hard than wood.

The roots of cycads look very unusual and are known as coralloid roots because they have a similar shape to coral. Their roots share an important relationship with the blue-green algae, cyanobacteria. The roots provide the cyanobacteria with protection while the cyanobacteria supplies the roots with nitrogen based nutrients.

Distribution of cycads

The distribution of cycads is naturally mostly limited to tropical regions. They are found naturally in every continent except Europe and Antarctica and are now also commonly planted garden plants.

Cycads are found in a range of habitats including tropical forests, seasonally dry forests and savannas. One species of the African cycads, genus Encephalartos, has evolved to withstand the stress of living in desert environments.

Typically, cycad plants are most successful in habitats with well-drained soils. They are found in a large number of places but are never the dominant plants of an ecosystem.

Diversity and taxonomy

There is currently around 250 species of cycads living on Earth. They were most diverse during the Jurassic Period when they made up around 20% of the world’s plant species.

The cycads are gymnosperm plants and hence sit in the class of plants known as Pinopsida. They form the sub-class Cycadidae and the order Cycadales which includes three families and 11 genera. The majority of species belong to the family Zamiaceae which contains around 130 species.

Evolution of cycads

Cycads are an extremely old group of plants. They are known to have been present at least 280 million years ago from the dating of fossils found in China. They were most abundant in the Jurassic Period between 201-145 million years ago, occasionally referred to as the ‘Age of Cycads’ by botanists.

Reproduction and dispersal

Cycads produce separate male and female plants with distinct cones. Cones are often brightly colored in reds, oranges and yellows. Pollination is believed to be mostly completed by weevils and small bees which are attracted to seeds by heat and scent.

They reproduce with seeds which have fleshy outer layers to attract animals. Animals are the main vector for dispersing seeds into new areas. Cycads often grow in open areas and new it is common for seeds to germinate following fires.

Interesting facts

  • Over half of the world’s cycads are threatened with extinction in the wild but are helped by the fact that many species are commonly planted household plants.
  • A number of species from the genus Encephalartos are referred to as bread palms because the insides of their starchy trunks can be used to make bread.
  • Cycads can produce dangerous toxins that can affect the nervous system of animals, cause vomiting, and lead to cancerous growths.

Last edited: 22 May 2015

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  • Cycads date as far back as 280 million years!
  • 305 species of cycads exist to date, but scientists estimate that the true number of cycads is much larger (more than 400 species in total).
  • Some species of cycads look like palm trees, while others look like ferns at first glance. Despite these similarities, cycads, palms and ferns are not genetically related.
  • South Africa is a global hotspot for cycads with 38 cycad species (37 species of Encephalartos and one species of Strangeria).
  • Most cycads are slow growing but can survive over 2000 years in the wild.
  • Cycads are considered as a status symbol all over the world. Older plants fetch thousands of rands and can substantially increase the value of your garden over time.
  • The price of a cycad plant depends on the age, size of the stem and species.
  • Cycads can survive in different habitats: tropical rainforests, deserts, swamps, sandy and rocky areas.
  • Cycads do not produce flowers. Male and female reproductive organs develop on separate plants (dioecious). Male plants produce egg-shaped cones that are usually yellow to brown in colour. Female plants develop ovules and seeds on leafy structures called sporophylls.
  • Cycads produce small seeds that are covered with yellow or reddish flesh. Even though seeds contain toxin, they are part of a human diet in some parts of the world.
  • Cycads are a source of food for many animals. Larvae of certain butterflies and ants eat secretion from the leaves, cattle feed on the leaves, while fruit bats eat the seeds.
  • Leaves and cones of cycads are used in traditional Asian medicine

What Are Cycads: Learn About Growing Cycad Plants

Going as far back as the dinosaurs, cycad plants are great for beginner and seasoned gardeners alike. These appealing plants will not only add interest both indoors and out, but they’re easy to care for. Let’s learn more about how to grow cycads.

What are Cycads?

Cycad plants are hardy, evergreen gymnosperms (cone-bearing plants) that grow in sand or hard rock. Cycads are dioecious plants; there are separate male and female plants. The female plant produces seeds, and the male plant produces cones filled with pollen.

The most popular cycad is the sago palm. They are slow growing and have a long life. They usually grow to 3 to 5 feet in height, although they can sometimes reach 10 feet in height.

Species of Cycad

Cycads have been referred to as “living fossils” because they have existed before the dinosaurs. There are roughly 300 known species of cycads and new species of cycad are still being discovered. Although botanists are discovering new species of cycads, they are becoming extinct; the main threats to the cycads are habitat destruction and the harvesting of the plant.

Cycads are often confused with palms in appearance, but they are not related as the cycad does not produce flowers or fruit. However, the cycad is closely related to the pine tree.

How to Grow Cycads

Because cycad plants are hardy, they are relatively easy to grow. The most important requirement is good drainage. If water is stagnant, the roots will rot. Cycads do well in terra cotta pots with a cactus mix or potting soil. Don’t expect rapid growth; these plants are slow growing, and like being root-bound, so there is no need to re-pot too often.

If you are planting the cycad for landscaping purposes, it is best to transplant a young plant from a container. The cycad does not like to have its roots disturbed until a trunk is visible. It is best to transplant during the spring when the temperatures are starting to increase. Remember that the cycad needs good drainage.

Cycad Care

Indoor cycads should never dry out. The soil needs to be kept moist but not saturated. In the summer months, your indoor cycad will need to be watered twice a week as opposed to the winter months when the plant will need little water. Keep this plant away from any direct heat sources and place it in a location where there is natural light.

If your cycad is outside, it will need full sun and your average temperature should be 70 F. (21 C.).

Fertilizing four times a year will ensure proper nutrition and growth. Typically, a granular fertilizer for palms with nitrogen (N), phosphorus (P), and potassium (K) that contains additional magnesium (Mg) and a complete micronutrient amendment is sufficient for cycads and will supply all the necessary nutrients.

The Cycad Pages

Cycas macrocarpa Photo Ken Hill

Introduction to Cycads

What is a Cycad?

The cycads are a small group of plants with many unique features, an ancient origin and a very long history. Cycads are known to have lived in the Permian era, over 200 million years ago – even before the dinosaurs roamed the earth. Although once abundant across the globe, the cycads are now greatly reduced in both numbers and distribution. There are now about 250 species in 11 genera, compared to possibly 300,000 species of flowering plants, the group that now dominates the world vegetation. All cycads are tropical or subtropical and each genus has a restricted geographical range.

The very large divided leaves means that cycad plants resemble palms or tree-ferns in overall appearance. Cycads, however, differ greatly in almost all aspects of detailed structure and reproductive behaviour. Cycad plants are dioecious (i.e. male and female reproductive structures are borne on separate plants), and reproduction is by seeds, which are produced on open carpophylls or seed-bearing leaves. Although technically woody plants, unlike other woody plants, cycads possess a pachycaul stem. This is a thick, soft stem or trunk made up of mostly storage tissue with very little true wood. Within the trunk, leaf traces or veins leading to leaves arise at a point opposite the attachment of the leaf, and circle the trunk within the storage tissue. These are known as with girdling leaf traces, and occur in some ferns but no other seed plants. The coralloid roots of cycads are also characteristics not seen in other seed plants, and the cycads lack the axillary buds seen in other seed plants.

The living cycads (division Cycadophyta) include about 250 species, with 11 genera in 3 families. The cycads have been classified as “gymnosperms” in the past, although recent studies have shown that this is not a natural group, some members being closer to the flowering plants than to other “gymnosperms”. The “gymnosperms” are all ancient seed plants, many now extinct, but with four major groups living today. These are the cycads (Cycadophyta), the Welwitschia group (Gnetophyta), the conifers (Pinophyta) and Ginkgo, the Maiden Hair Tree (Ginkgophyta). They are now regarded as quite separate and distinct classes of equivalent status to the flowering plants (Angiosperms or Magnoliophyta). Although the four groups of “gymnosperms” are very different from one another in appearance they all produce naked ovules in contrast to the flowering plants in which the ovules are enclosed in an ovary.

The Cycad Pages

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Cycad

Cycad, any of the palmlike woody plants that constitute the order Cycadales. The order consists of three extant families—Cycadaceae, Stangeriaceae, and Zamiaceae—which contain 10–11 genera and 306 species. Some authorities use the term cycad to refer to all members of the division Cycadophyta. Plants of this division are known to have existed in the Mesozoic Era, about 252.2 million to 66 million years ago. Only the order Cycadales contains living species.

Cycad (Cycas revoluta).Knut Norstog

Cycads are gymnosperms distinguished by crowns of large pinnately compound leaves and by cones typically borne at the ends of the branches. Some cycads have tall unbranched trunks with an armourlike appearance; others have partially buried stems with swollen (tuberous) trunks. The stem has a large pith surrounded by a narrow zone of soft woody tissue. Male cones produce pollen that is carried by wind to female cones (borne on separate plants), where fertilization occurs.

Slow-growing cycads are used as ornamental conservatory plants, but some survive outdoors in temperate regions (see Cycas). Starch from the stems of some cycads is edible after an alkaloid is removed by thorough cooking. The young leaves and seeds of other species also are edible.

The desirability of cycads as specimen and ornamental plants in gardens and greenhouses has led to the overharvesting of many species from the wild. As a result, some species are nearly extinct in nature, and a number are critically endangered. Most cycads are protected by conservation laws in their native countries. International trade in cycads is controlled by the Convention on International Trade in Endangered Species of Wild Fauna and Flora.

Karoo cycadKaroo cycad (Encephalartos lehmannii).© Harm Kruyshaar/.com Get exclusive access to content from our 1768 First Edition with your subscription. Subscribe today

Cycad

Scientific Classification

  • Kingdom: Plantae
  • Subkingdom: Tracheobionta
  • Division: Cycadophyta
  • Class: Cycadopsida
  • Order: Cycadales

Families

  • Cycadaceae (cycas family)
  • Stangeriaceae (stangeria family)
  • Zamiaceae (zamia family)

Cycad is a term that refers to a group of cone-bearing plants that are considered living fossils. Actual fossils of such plants are dated by radiometric dating to have an age of supposedly 240 million years. These unique plants remain largely unchanged since plants like them were fossilized. In the modern world, most species are endangered and some are now even extinct. The sago palm is the most well known cycad.

Contents

  • 1 Anatomy
  • 2 Reproduction
  • 3 Ecology
  • 4 Related References

Anatomy

The cone shaped reproductive structure of a Cycad

Most cycads have wide, short trunks and frond-like leaves. The trunks can live underground or above ground. The leaves of the cycads contain poisonous chemicals and if the plant is used for food, which it often is, then these chemicals must be removed. The cycads also contain one or more cones. Roots called coralloids form near the surface of the soil and contain a type of bacteria which fixes nitrogen for the plant and in turn helps the plant create its own fertilizer. This nitrogen-fixing ability allows the cycad to grow in very poor soil and establish a competitive ecological niche.

Reproduction

Cycads can reproduce via asexual or sexual reproduction. When it comes to asexual reproduction the Cycads produce stem offshoots or pups. For sexual reproduction cycads are dioecious, which means plants are either male or female. The reproductive structure is specifically called a strobilus or cone. This is a group of leaves which bear either pollen or ovules which become seeds after fertilization. There is a visual difference between the males and females, males are more slender and possesses smaller sporophylls while females are larger and have fewer sporophylls.

Cycad fruit.

Ecology

Cycads are long living and slow growing. Their stems are highly susceptible to fungal attack. Cycads grow well in well-drained soils, making most Cycads’ habitat that of a tropical or subtropical climate in regions with summer rainfall. They are found on every continent except Europe and Antarctica. The seeds of cycads are large and brightly colored, including the colors red, purple, and yellow. The colors attract birds and a variety of mammals which disperse the seeds.

Related References

  • Cycad Cycad Identification
  • wikipedia Wikipedia
  • Cycad History of the Cycad
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When we think about plants, swimming ability generally doesn’t come to mind. As kids we learn that one of the major differences between plants and animals is that plants generally can’t move on their own volition. Certainly there are exceptions to this rule – sensitive plants and Venus flytraps to name a few. However, there are plants out there in which swimming is a crucial component of their life cycle. Though it isn’t the plant itself that does the swimming, some of the ancestral plant lineages alive today have motile sperm!

Swimming sperm is a throwback to the early days of plant evolution. Because they arose from aquatic algae, a sperm’s ability to swim to an ovule helped increase the chances of reproduction. Today we see this adaptation in plants like liverworts, mosses, and ferns, which still require water to complete their life cycle. However, swimming sperm are not restricted to the cryptograms. This adaptation also can be found in cycads (as well as ginkgoes). Their sperm are super strange too. They look like little seeds covered in concentric rings of beating flagella. Unlike cryptograms, however, their swimming ability doesn’t come into play until pollen comes into contact with the ovule.

If you had to guess which organism possesses sperm with 40,000 tails, what would you guess? Elephant? Whale? Chuck Norris? Would you have guessed that it belongs to a plant?

This is the sperm of Zamia roezlii. It has a flapper dress-like fringe of tens of thousands of flagella to turbo-charge its way to eggs.* That a plant should possess sperm with such horsepower is all the more surprising given that most plants have sperm with no tails at all. A pollen grain is actually a tiny haploid plant called a male gametophyte. In most flowering and coniferous plants a pollen grain produces two tailless sperm who travel down a burrowing pollen tube to reach the female gametophyte buried inside a cone or flower — no tails needed.

Ancestral plants tend to have swimming sperm because land plants evolved from aquatic green algae, where the swimming — and fertilization — was easy. A few ancestral plants like mosses still have sperm with tails and rely on a watery film on the surface of the plant for the sperm to get from Point A to Point B. But they are such lousy swimmers that some mosses resort to Plan B: they make special leaves folded into little splash cups, and when a raindrop lands in them, their architecture blasts sperm inside skyward in an attempt to Fed-Ex them to the vicinity of a receptive female. So turbocharged swimming plant sperm is definitely an oddity.

To which plant does this impressively-endowed sperm belong? A cycad.

OK, so what’s a cycad? This is a cycad.

Not dinosaur eggs — but something that the dinosaurs might have seen. Creative Commons kiryna. Click image for license and link.

Here’s what they typically look like in profile. These are mature, juvenile, and seedling cycads of the same species.

Creative Commons Esculapio; Click image for license and link.

Cycads are old. Way old. They were the dominant plants during the Mesozoic, the age of the dinosaurs, as seen in countless ancient murals. At least that was the dogma for many, many years. But recently a widely reported studied was published that undermines that idea — if you look at it in a certain way. But before we come to that, let’s look at what cycads are and at their surprising biology.

Sometimes called sago palms, cycads are in no way palms. Palms are flowering plants. Cycads, like pine trees and juniper bushes, are gymnosperms — “naked seed” plants. In other words, they make seeds, but they don’t make flowers or fruit as a way of bringing those seeds into the world or sending them on their way. Seeds were a great evolutionary innovation for plants, because they allowed them to package a little plant embryo that has already begun to develop — perhaps even a little root and a few small leaves — with a little stored food in a dessication-resistant shell.

A seed is a way of giving a young plant a jump start on life and a little food for the road, not unlike the relatively contemporaneous innovation of amniote eggs in land vertebrates. Microscopic spores — the previous dispersal method still employed by mosses, lycopods, and ferns today — are much more prone to drying out or landing in a place far too inhospitable for germination. Seeds help increase the chance of success.

A cycad plant is a column or trunk of old leaf bases surmounted by a cluster of new leaves. Cycad leaves are wonderful to touch, if you ever get the chance. Strappy, leathery, tough, and often blue-green, there’s something delightfully primeval in the way they feel (although, it should be said, the much-older mosses have delicate, thin leaves**).

Cycads also have an interesting symbiosis with cyanobacteria, also called blue-green algae, just like some lichens. They make special “coralloid roots” that grow upward in a very un-root-like fashion. In return for feeding, housing, and hoisting their cyanobacterial symbionts above-ground inside these structures, the cyanobacteria provide the cycad with that most limiting of bio-nutrients: fixed nitrogen.

In addition to having super-charged sperm, the pollen of cycads has another interesting habit that they share with their close relative, Gingko. When their pollen arrive on a female cone (usually via weevil, beetle, or wind), they start to grow into an ovule. Once there, they send out a long tube into a part of the ovule called the nucellus and send out a haustorial structure that sucks up nutrients from the host female. Haustoria are also used by parasitic fungi that penetrate their plant hosts.

In cycads, the haustorial pollen tube ends up destroying most of the tissue into which it penetrates, although this tissue is a) not part of the future seed and b) technically expendable because once a cone is fertilized it is not used again. But imagine, if you will, that every time human sperm landed in a uterus, they implanted in the uterine wall, sucked up nutrients and grew into little organisms of their own for a while, and only then released the gametes that would go on to fertilize the egg. That should give you the general, somewhat unnerving idea.

Like most gymnosperms, cycads make both male and female cones, but unlike many conifers, they bear only male or female cones on a given plant. That is, there are girl cycads and boy cycads. The female cones make seeds and the male cones pollen. In the photo at top are female cones with seeds inside. When you break them open, you often find brightly colored seeds, like this, or this:

Disemboweling a cycad cone. One of the brightly colored seeds is visible in the subject’s hand. Creative Commons Sharktopus; click for license and link.

Because cycads are gendered, that means it’s also possible to end up all alone. Indeed, as Robert Krulwich reported recently on his blog, that has been the sad fate of a cycad found in Africa 100 years ago and sent off to the Royal Botanic Gardens at Kew. It’s a boy. And unless someone finds a female to keep it company, it will be the last of its kind.

Cycads have received a bit of attention lately. Many cycads contain carcinogens or neurotoxins or both. In Oliver Sacks’s Island of the Colorblind, he relates his fondness for cycads (a love I share) and his frustrating investigation into a mysterious devastating neurological disease among the people of Guam that may be linked to their habit of pounding up seeds to make cycad flour. Lately, suspicion has fallen on the practice of eating bats who may have concentrated cycad neurotoxins in their bodies.

That brings us back to the question of their antiquity. Cycad fossils date back to at least the Permian, and possibly the Carboniferous, 320 million years ago, the age of giant coal-forming swamps and disturbingly large dragonflies. But they flourished during the Mesozoic — the “age of the dinosaurs” — and probably were dined upon, and certainly trod upon by dinosaurs. They may also have been the first insect pollinated plants when beetles took up the habit of eating — and generally living in, wallowing in, and spreading around — cycad pollen, a tradition they continue today. But a recent study in Science reported here, here, and here finds that, according to their DNA, the 300 modern species of cycad evolved a paltry 5-12 million years ago.

OK, so the species alive today were not those alive during the Mesozoic. I accept that. That, in of itself, that is interesting news — their diversity declined in the wake of the Big Impact, and seem to have rebounded and re-speciated during some sort of worldwide climatic change. But the authors make a big point about us not being able to call cycads “living fossils” because they are not the same species we find in fossils.

Hold up there. They still look like ancient cycads. They still make seeds like ancient cycads. Their tailed sperm still betray their ancient origin, and the ancestral condition of all land plants, presumably just like ancient cycads. Survey says: They’re still cycads. And cycads are still old. And so, in my opinion, when you visit cycads at botanic gardens or see them in someone’s yard, it’s still OK to think of them as ancient, and imagine these extraordinary creatures among the dinosaurs.

**OPTIONAL BIONERD TECHNICAL DIGRESSION AND SOAPBOX ALERT**

You learn quickly in biology, as in our lives, nearly everything is a gray area. Life is a continuum of form and function. We try to impose neat conceptual order on it to make it easier for us to understand and discuss, but no sooner have we done it than we find some (or many!) creatures that throw wrenches in the cogs.

Take, for example, the term “species”. If you really want to light a match in a room full of ideological fuel, ask a group of biologists to define that term. Better yet, study life long enough and you’ll realize “species” has completely different meanings among various groups of living things, and especially bacteria and archaea, where inter-species sex is common and species-defining mechanisms like reproductive or geographical isolation that work fairly well in animals are often meaningless.

I’m not saying we should ditch the concept “species” or even get rid of binomial nomenclature, the double-named system devised by Carolus Linnaeus for calling species by name (think: Homo sapiens). I think it still has great value for humans to think of living things in terms of species — many of which are easily discernable and very “real” — and to give them names and not (forgive the term) dehumanizing barcode numbers, as some have proposed.

BUT, perhaps we should not be so finicky about the term “living fossil” with regard to species. Perhaps cycads have changed a little bit from their days of the dinosaurs. Perhaps they’re not the same “species”. If they look more or less the same and are doing more or less the same things in the same ways, that’s good enough for me. They are still recognizable ancient forms, and they’re still alive.

I, for one, love “living fossils” because it helps make things vivid for non-scientists. It helps people engage their imaginations. Because unless you know their story, and their history, cycads might just seem like a boring palm-thingy, and a cycad fossil just “a leaf”. When you read that cycads are living fossils, and that something almost identical lived among dinosaurs and giant ancient dragonflies, and that today they possess perhaps the most well-endowed sperm on the planet, and that you can still touch their living, breathing descendants today, your eyes may be opened that they are so much more.

*I’m sensing some latent flagella envy among some elements of my reading audience. Kinda reminds me of those guys with three or four outboard motors clamped to the back of their motorboats, if you know what I mean.

** Technically, “phyllids”. Only vascular plants (those possessing conducting tissues for water and sugars like xylem and phloem) have true leaves, according to botanists.

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