GAMBLE OF A LIFETIME
I learnt a new word: semelparity. It is when an organism only reproduces once, then dies. Salmon, eels, cicadas and most bamboos are semelparous.
B ut if an organism can reproduce repeatedly during its life, this is called iteroparity, as in the word (re)iterate. And of course the majority of more complex plants and animals, including us, is iteroparous.
Don’t even think about pronouncing it. Well OK, I think it rhymes with hippopotamus… I can feel a silly poem coming on.
This all started when I searched the internet for information about Strobilanthes gossypinus.
This beautiful silver-grey Indian shrub was introduced in about 1997, and many people around northern New Zealand have planted it in recent years. I discovered from Auntie Google that it is semelparous. It lives for 13 years, then the entire species flowers and produces seeds simultaneously worldwide and dies. New plants grow from the seeds and it all starts again.
I also discovered – after 20 years of calling it Strobilanthes gossypinus – that its proper Latin name is actually
Strobilanthes lanatus. Its common name when at home in southern India’s Western Ghats mountain range is kurunji (or kurinji), although this local name also covers the more common Strobilanthes
kunthianus which does not seem to be here in New Zealand.
On top of all this disturbing news, I also found in the same Wikipedia sentence that Strobilanthes lanatus is a mast seeding plant. Mast seeding is when the entire population of a species produces a
massive crop of seed simultaneously after several years of little or no seed production.
(‘Mast’ here refers to the German word for fattening livestock on abundant seed or grain.)
The Strobilanthes lanatus plants in New Zealand flowered for an 18 month period through 2010 and 2011. And as they are semelparous, they all died by the end of summer 2011, leaving millions of plump seeds scattered nearby. It was like a garden version of the last scene of Hamlet; corpses everywhere and rather a lot of wailing and gnashing of teeth from the gardener (me).
However, young seedlings started popping up soon after the carnage was over. Its gratifying that they only do this every 13 years as it gives us plenty of time to remove any surplus seedlings. They grow where the seed falls from the old plant so they don’t disperse more than a metre or so and the threat of general weediness doesn’t seem likely to be an issue.
Strobilanthes lanatus is easily propagated from tip cuttings in spring and summer at any stage of its life cycle. And even three-month-old rooted cuttings flowered and died in step with their plump and elderly mothers… cue more wailing.
It seems that mast seeding has evolved as a way of outwitting seed predators.
By occasionally producing far more seed than the local seed-eating animals can cope with, there is plenty left to grow into new plants.
Native beech trees are mast species, producing a mast crop every three to six years. The rare ka¯ka¯po¯ only breed during the abundance of a beech mast year. Rimu, kahikatea, flax and some tussocks are also mast seeders and so are many oaks, maples, birches and conifers, but none of these is semelparous.
Semelparous mast seeding is an even bigger gamble for a plant species to take.
Each generation only gets one shot at it.
In northern New Zealand gardens, the kurunji combines beautifully with almost any other plant because the colour, form and textural contrasts are so striking. In full sun, they form rounded, dense mounds of silver-grey, furry foliage up to 2m high and wide after a few years, but they respond readily to hard pruning or frost damage by popping out fresh new growth within a few weeks.
In the shade of larger trees, the kurunji is more open and will grow taller. In this situation they are protected from all but severe frosts.
In dappled light, the combination with clivia and the shade-loving Ajuga reptans ‘Catlin’s Giant’ can make an arresting sight in spring.
So now that we in New Zealand have seen a full life cycle of this lovely plant we know what we’re in for. It will start to flower and die here and everywhere else in the world around 2023.
Meanwhile, I’m left struggling to suppress the emergence of some ghastly blurt of doggerel concerning the muddy adventures of the iteroparous hippopotamus…
Joe Bennett would surely know what to do next!