Cycads; ancients with an amazing sex life!

Cycads, now a small part of the world's vegetation landscape, once dominated it. Their fossil record goes back unambiguously to 280 million years ago, with ages of over 300 million years often suggested. The younger figure is still 40-50 million years older than the first dinosaurs; this is a truly venerable plant lineage. The first flowering plants, which in time would overwhelm the cycads with a huge diversity of species, didn't appear for another 135 million years (ie 145 million years ago)!

Burrawangs Macrozamia communis, Nelligen, south coast New South Wales. Cycads have long lived in the
metaphorical shadow of flowering plants, as these common NSW coastal cycads do literally, under
the Spotted Gums Corymbia (formerly Eucalyptus) maculata.Like many cycads, the trunk of this species is underground;
no other cycad in the world grows further south than this one.

Now there are now only around 260 cycad species remaining, scattered throughout the world's tropics and subtropics, usually in drier situations (compared with at least 250,000 flowering plant species). Their superficial similarity to palms can be seen in the photo above, and is often remarked upon. It is totally coincidental however, as palms are true flowering plants.

Nonetheless, this Macrozamia riedlei (here in Coomallo Nature Reserve north of Perth) is often known as Zamia Palm
(or just Zamia) for understandable reasons. It is restricted to dry forests, especially Jarrah Eucalyptus marginata, in the
south-west of Western Australia. It was named for Anselme Riedlé, chief gardener (of a team of five)
on the mighty Baudin expedition of 1800-04, who almost certainly collected the first specimen at
King George Sound (now Albany). Sadly he died soon afterwards in Timor, aged just 26.

Cycads arose, as we have noted, in an unimaginably distant past before flowers developed. They reproduce by pollen transfer between cones on separate male and female plants. It was long assumed that this could only be achieved by wind and chance and that only flowering plants utilise animal pollinators, but these notions have now been challenged by detailed observation of several cycad species. It seems undoubtable now that cycads employed insects to efficiently transfer pollen from male to female cone long, long before flowering plants reinvented the trick. One of the first approaches in such studies is to exclude insects, but not wind, from female cones, and vice versa - repeatedly it transpires that pollination can take place without wind, but not without insects, especially beetles and particularly small weevils. We don't normally think of beetles (other perhaps than jewel beetles) as significant pollinators, but in this case it makes sense as beetles were around, with ancestral cycads, well before moths, flies or wasps were.

In some cases beetles have been observed pupating within the males cones, emerging with pollen attached to hairs on their legs and moving to female cones, entering them when they became receptive. Something must be attracting them. Observations on the NSW south coast Burrawang showed that adults and larvae of one species each of both weevils and thrips (a large order of tiny sap-sucking insects) were feeding and breeding in male cones, and later moving to female ones.

Female Burrawang cones, Nowra, New South Wales.
What's going on to strongly attract insects to them?

Studies of other Australian Macrozamia species revealed some remarkable adaptations on the part of the plants (which have had, after all, plenty of time to develop them!). Thrips like cool, dry, dark places and Macrozamia cones usually fit the bill perfectly. However sometimes the cones go to great lengths to expel them. The cones heat to 40 degrees C, and emit water vapour, carbon dioxide and unpleasant terpenes, which causes the thrips to leave en masse; many of them find refuge in nearby female cones and the pollen is transferred.

Some beetles however quite like it hot, and back in the early 1990s work done on the West Indian cycad Zamia pumila showed that in the evening when beetles were active the male cones heated by as much as five degrees, at considerable cost as starch and fat levels in the cone dropped considerably at the same time. The heat also vapourised a chemical with a "sweet minty" scent (in the opinion of the researchers, but the beetles clearly liked it to), and released a sweet secretion, all evidence that the presence of the beetle was worth a lot to the cycad. The beetles were impressed, spending time and even mating in the cone. This study didn't look at the role of the female cones (curiously perhaps) but more recent ones have.

A south-east Queensland study did so and found another version of this fascinating story. Macrozamia lucida is a species from wet eucalypt forests in south-east Queensland, whose male cones harbour large numbers of thrips which eat the pollen but also carry some of it.

Male cones of MacDonnell Ranges Cycad Macrozamia maconnellii, a close relation of M. lucida.

For about four weeks of the year the M. lucida cones produce pollen, and at this time they also go to considerable lengths to expel their thrip tenants. Each morning the cones burn energy to raise their internal temperature by up to 12 degrees! At the same they they emit high levels of beta-myrcene (widely occurring in aromatic plants but also employed in the perfume industry) which has a "harsh, overwhelming odour" (again the researchers' opinion, but again the insects seem to agree). The thrips all flee, carrying pollen with them. And here it gets really interesting because the female cones now emit modest doses of the same chemical, but at lower levels the thrips find it attractive so they seek shelter there - and the plant's job is done! Then the male chemical levels drop again and the thrips return, and the performance is repeated daily until the male cone's reserves are depleted and the female is well-fertilised.

There are just three living families of cycads, and one of them (Stangeriaceae) comprises only three species, one in South Africa and two in Queensland. The largest is Zamiaceae with some 150 species in the tropics and subtropics of the Americas, Australia and Africa (though higher numbers are sometimes cited too). One subfamily of two genera is represented in Australia, and limited to it. There are about 40 species of Macrozamia, and just two of Lepidozamia. Some Macrozamia are common and familiar in their ranges. We've already met a couple but it doesn't hurt to renew our acquaintance.

Burrawang, Nowra, New South Wales.
This forms a near-dominant understorey to the lovely Spotted Gum coastal forests in places.
This is one of several species the seeds of which Indigenous Australians processed via a days-long
complex process of crushing, soaking and heating to denature the virulent toxins. It has always fascinated me
that people would make the assumption that a food which was fatal could be made edible if they
experimented enough - especially in a food-rich environment like the NSW coastal forests.

Macrozamia moorei, here near Springsure in central Queensland, is common in a limited
area of dry ranges inland from Rockhampton to Maryborough. It is probably
the largest of its genus, growing to tree size.

Macrozamia secunda (here in Goobang NP near Parkes, NSW) by contrast is one of the smallest,
with an underground stem and only one to four fronds which mostly grow close to the ground.
Distinctively the pinnae ('leaflets') grow on just one side of the stem.
Its habitat is dry open forests on the hot mid-western slopes of New South Wales.

One of the best-known Australian cycads however has one of the smallest distributions. The MacDonnell Ranges Cycad, introduced earlier, lives only in the dramatic MacDonnell Ranges of central Australia around Alice Springs and the nearby George Gill Range. They are relics of a wetter past, isolated in the relatively sheltered central ranges by the surrounding deserts.

McDonnell Ranges Cycads clinging to the gorge walls in the ranges;
at Ellery Creek Big Hole above, and Standley Chasm below.

The two Lepidozamia are widely separated in distribution, and both restricted. Lepidozamia hopei, reputedly the tallest of all cycads, towering to 20 metres high, lives only in the Queensland Wet Tropics rainforests. L. peroffskyana, far to the south, has a slightly larger range in wet forests on steep slopes from south-east Queensland to north-eastern New South Wales.

Lepidozamia peroffskyana in wet forest on North Brother Mountain, Dooragan NP near Port Macquarie,
north coast New South Wales. Note the huge female cone.
Weevil pollination has been demonstrated for this species too.

The third family is Cycadaceae, which comprises only the genus Cycas, with some 110 species from east Africa and Madagascar to south and south-east Asia through northern Australia to the Pacific. Perhaps 30 of those are Australian; here are three of them. It is a feature of Cycas that the female doesn't form cones, but carry hard spherical seeds on flattened drooping stalks called megasporophylls - in practice these are best considered 'opened-out' cones. They appear in a couple of these photos.

Cycas media is a common cycad in the woodlands of the Top End around Darwin in the Northern Territory.
It is atypical among cycads in being deciduous in the dry season; this plant is producing new growth.
The megasporophylls are obvious.

Cycas media in the understorey of dry monsoon forest south of Darwin.

Cycas calcicola in a burnt landscape at Litchfield National Park south-west of Darwin.
This is a very restricted species, growing only on limestone outcrops near Katherine (hence calciola)
and here on sandstone slopes in Litchfield. Any plant up here must be fire-tolerant.

Lastly Cycas media is a common cycad in drier forests subject to regular burning in east coastal tropical Queensland. Some authorities say that it is also found in the Top End and northern Western Australia, some do not. I'm still trying to fathom this one.

Flourishing Cycas media, Redden Island, Cairns. Both this specimen and the next display megasporophylls.

Cycas media with new growth, Cooktown.

Cycads are old, magnificent, fascinating - and arguably raunchy. I hope you love them too.

NEXT POSTING THURSDAY 5 DECEMBER
(And remember that you can get a reminder when the next post appears by putting your email address in the Follow by Email box in the top right of this screen.
And I'd love to receive your comments - it's easy and you don't need to sign in!)