Tuesday, 25 March 2014

The coning of the dioon


To paraphrase the 1843 paper describing this species for the first time, the addition of a new cone to our Cycadaceous collection is indeed a fine thing. Over the last month or so, one of our cycads has been constructing its first cone. Exciting times in the nursery at Royal Botanic Gardens Melbourne.

It's also the first time this particular species has 'coned' in our care, and it's a girl**: cycad plants are either male or female. Although 'commonly cultivated' according to Gardening Australia's Flora we have only one specimen of Dioon edule. And a pretty little species it is, with a lovely waxy bloom on its leaves (which may fade with age).

Our cycad growing expert, Dermot Molloy, describes the species as a very hardy Dioon from the Sierra Madre Oriental Mountains in Mexico. Loran Whitelock, in his book The Cycads says this species grows naturally in rocky areas and cliffs between tropical deciduous forests and oak woodlands. There are number of separated populations, each of which has gathered its own distinct leaf form and colour.

Whitelock says the current split into two varieties (one from the states of Nuevo León and Tamaulipas, and sometimes considered to be a distinct species called Dioon angustifolia) is simplistic. Eventually, he says, with more study, there will be more species named. So the important thing is to know where your specimen is from. Whitelock documents five variants: Valles, Río Verde, Querétaro, Jacala and Palma Sola.


Our seed came from somewhere a little closer to home, a grower called Peter Heibloem, at Eudlo Cycad Gardens in Nambour, Queensland. Peter collected all over the world in the late 80's early 90's but unfortunately he didn't provide a precise location for this collection. While the waxy grey foliage is distinctive, it doesn't seem to be a useful identification character.

Sydney's The Cycad Pages is a little helpful, citing three groups on the advice of Jeff Chemnick. The diagnostic features are whether or not the leaves (the full 'fronds') are flat or keeled, and the degree of overlapping of the individual leaflets. Ours have pretty flat leaves with leaflets that hardly overlap. This, I think, puts them in with the first described population from Chavarillo (Vercruz), or perhaps Rio Pescados which is similar. That's a good, and as close, as we can get at the moment.


The species as a whole is not uncommon, or under great risk, yet many have been collected from the wild for cultivation or lost through land clearing. There is an unfortunate market in the head (including the growing tip) with the leaves intact as a decoration. This stops the plant being able to produce new cones. Given the variety within the species it will also be important to conserve individual populations. As the species name implies, the seed has been eaten by humans in the past, but not much today.

Even if we can't track down the variety (named or unnamed) it's a pleasure to have a Dioon doing its thing. 'Dioon' is Greek for two eggs, a reference to the pairing of seeds within the cone, something we won't get to see without a male plant. There are 10 more species, all but one (which is found further south, in Honduras) from the coastal mountains of Mexico. Most develop long trunks, up to 15 m tall, making them look very palm-like at a distance.

Dioon edule reaches only three metres, at most. Ours is young and barely above the ground. It has grown from a seed sown on 31 March 1992 so it's taken 22 years to produce this cone, starting as a bump on 20 February and turning into this last week.


We'll be on the watch out for a sticky secretion, indicating that the ovules** are mature and the plant is ready to accept and draw down any pollen that lands on the cone. As you know, that won't happen this time because there are no males around to provide the pollen needed. But plenty of opportunities to come, this being only the first of hopefully many cones. Cycads can live, in the wild, for up to 1000 years. Take a look at this 240 or so year-old Encephalartos altensteinii in Kew Garden's Palm House. It's thought to be one of the oldest pot plants on Earth and was viewed, in fruit, by Sir Joseph Banks in 1819. Perhaps our dioon will attract similar attention on one of its next conings*.


* As distinct from coning and coning.
** Well, we made a mistake. Our girl is a boy! I've posted an update, with pictures, on 2 April 2014.

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