The Karvy Question
There is a shrub – an omnipresent one – on the gentle as well as steep slopes of the Western Ghats called Karvy (or Karvi), Strobilanthes callosus. It grows in dense thickets with its stems shooting straight up from the ground into a loosely held bunch. In summer they appear as a maze of bone-dry sticks which are collected by local communities to build walls – the sticks, being straight, are tied next to one another upon which a layer of mud and dung is plastered (these structures are very cool and very sustainable in their make). By late winter the leaves dry out, first developing warts, then turning yellow and orange, and then as they desiccate with rising temperatures they turn brown and crumble away.
|A carpet of Karvy, Strobilanthes callosus, the one with dark green leaves predominates on one of the slopes in Sahyadris, the northern Western Ghats. September 2011.|
It is between these two seasons that they’re at their best – their leaves are dark and large, crenate, and shaped roughly like a spearhead. Right at the onset of monsoons, the new leaves arise in a bunch, and slowly regain their spread over the Ghats. They look marvellous, whether bare or cloaked, giving the basalt slopes of the Ghats their own signatory patterns and colours. If you’re a trekker you’ve come across these industrious plants blocking the old path that leads to the fort – you will find them where no trees grow, and they often form a mosaic of light-and-dark hues of greens with the grasses forming their own patches in-between.
|A path through a Karvy grove in Sanjay Gandhi National Park. December 2012.|
They are mostly invisible for us. Their life is rather uneventful for the most part, if I may say so on behalf of the plant world. A few bugs, beetles, moths, and butterflies like the Southern Blue Oakleaf, are fond of munching on their leaves, some probably bore into their leaves and stems and roots. They are not visited by bees and butterflies, and are quite passive in their interaction with other living beings; introverts of the plant world, someone would say. But they’re crafty. Once in every eight years – that is nearly 2920 days – or about 3000 days, if we round it up – they show their true colours, envious colours, if I may again express the feelings of the plant world.
Every eight years, almost suddenly for those like me who don’t keep a count, they flaunt their most outlandish colours everywhere they’re present. Little green cone-like buds appear all the way on their straight nonchalant stems just after the first monsoon rains, which then turn to a soft pink, and as monsoon progresses bloom into purple-violet flowers, colouring the Ghats with their aura. Karvy is one of the plants called the plietesials – “plants that grow for a number of years, flower gregariously (synchronously), set seed and then die” (read more about it here). The other more common plietesial we know is bamboo, especially Bambusa bambos and Dendeocalamus strictus which flower anywhere between seven or fourteen or even fifty years.
|Karvy blossom in 2016 being paid a visit by a diligent Indian honeybee (Apis dorsata).|
Karvy belongs to the family Acanthaceae, and is one of the 450 species under the Strobilanthinae subfamily. The genus itself contains about 300 described species (Carine and Scotland 2002), with 116 recorded in India (Singh and Diwakar 2007), several of them, like Karvy, are endemic to India. It is a diverse taxa with some species that flower and fruit multiple times in their lifespan, such as plants like apple, cashew, rose, which are called polycarpic, and some that are monocarpic – they flower and fruit once and die, such as the ephemeral flora including rice and wheat and wild grasses which we see in abundance during monsoon and die after seeding. Karvy is therefore a monocarpic plietesial plant – the one which not only flowers only once in its lifetime but does so once every several years.
Me and my friend Alok, who’s a grass taxonomist, were on the lookout for something even rarer which we could not see when we came across groves of Karvy in bloom in Sanjay Gandhi National Park. It felt like meeting an old friend after eight years – but of course, that old friend we had met in 2008 (when I had started this blog and had only mentioned Karvy in the passing!) was long dead: Karvy is a plant that, after mass seeding, dies off. Mass seeding is a phenomenon called ‘masting’ which is “the intermittent production of large seed crops by a population of plants … is most likely in long-lived plants, which are less affected by the costs of not reproducing in some years” (Kelly 1994, he characterised Strobilanthes as a “strict masting” plant). We were in fact meeting the sons and daughters of our plant-friend, and it was a pleasant meet.
On the way we also stumbled upon Alok’s professor, who posed a very indulgent question to the young PhD scholar – of course most of their conversation about the conflicting taxonomy of grasses – which I adore too, and actively identified at least one genus to Alok’s surprise – left me clueless, he spoke of “problem solving” as an objective that was by-and-large getting lost in research. Alok and I agreed, but that got me wondering about “problem solving” in my quest of finding things out.
Coming back to Karvy, it posed a few questions even though its taxonomy was quite clear, so was the fact that it flowered once every eight years, as did its cousin Strobilanthes sessilis (locally called Topli Karvi) which grows on even harder ground such as the tabletops of the northern Western Ghats, and other slightly distant cousin Mackenziea integrifolia (synonymised with Strobilanthes perfoliatus) which is found in the evergreen forests of the northern Western Ghats. S. sessilis flowers every eight/seven years and S. perfoliatus every – wait for it – eight/seven years too! Strobilanthes kunthianus which grows in the high altitude shola ecosystem of southern Western Ghats blooms every 12 years.
|An Indian honeybee (Apis dorsata) visits Strobilanthes perfoliatus (= Mackenziea integrifolia) in Matheran.|
The first question was: why eight, or seven or twelve years; why not every year, or every ten years; the second question was: why are all of them in the shade of violet, why not yellow or red; and the final question, which is actually an extension of the first and second: how do they manage to get pollinated from animals such as insects without being bothered about them for all these years, or, in other words, how do insects cope after the sudden surge in food production that lasts only for about 120 days, or, and lastly, does mass flowering of Karvy affect the biomass of insects?
This article is largely about pondering over rather than solving the problems posed by Karvy for being too crafty and stunning at the same time.
Kelly (1994) has summarised eight hypotheses for the phenomena of masting (do read the paper, it makes for a lovely read on plant ecology) based on pollination and dispersal by wind and animals, predator satiation (or destruction of crop to satisfy a herbivore’s hunger), accessory costs and large seed size (basically spending less on more production at once), and resource matching and environmental prediction which requires the plants to “match the varying resources available” under favourable conditions for reproduction and establishment (see Table 2 on page 468). Karvy’s (S. callosus) ecology is not clearly understood as its phylogeny. Its spread in the northern Western Ghats is of 500 km and more, and it is quite predominantly present across the escarpments wherever it is suitable to be considered ‘common’. There’s no doubt that Karvy is so eccentric because it is coded in its genes. Yet I wonder if the climate made it so – Karvy flowering periods of 2008 and 2016 do not seem to show any correlation to monsoon extreme events, it does however indicate a positive correlation with ‘normal’ rainfall. Unfortunately we do not have data for previous years’s flowering, but if we go back every eight years from 2016 and 2008 to 2000 to 1992 to 1984, it all coincides with what is considered normal rainfall (see the summer monsoon rainfall data here). Of course, this is a naïve assumption, but it hints at Strobilanthes playing to the hypothesis that resource matching and environmental prediction, based on monsoon in the Indian context, could determine the period it takes – that of about eight years, and it holds true for both S. callosus as well as S. sessilis. Things however probably play differently for S. perfoliatus, which, although it shares more-or-less the same ecosystem, last flowered en masse in 2012. Going back every eight years, it must have flowered in 2004, 1996, and 1988, and so on – all these years, too, received normal rainfall.
|Sporadic flowering of Karvy in Bhimashankar Wildlife Sanctuary, photographed in October, 2011.|
What’s interesting about Karvy’s lifecycle is that once fertilized, the seed capsule ripens slowly over prolonged dry and hot weather of winter and summer, and often they grow on the parent body with the onset of next monsoon – another phenomenon we’ll introduce here is vivipary, where the mother plant carries the sapling until it takes birth and then are shed down with the next year’s rain instead of directly shedding the seeds. That means we need to look at how the rainfall was in the year – excepting 2017 – 2009, 2001, 1993, and 1985 for S. callosus and S. sessilis; and 2013, 2005, 1997, and 1989 for S. perfoliatus, one year after the mass flowering episode. For the former two’s progeny, 2009 and 1985 were drought years, and for the latter, 1989 was a drought year. There is not enough inference from this, but it is worth considering the debate whether Strobilanthes requires more resources, especially water, to produce flowers and seeds and less to germinate them. It must be remembered that Karvy, although a strict masting plant, also has vagrants lurking here and there. A small patch of Karvy blossomed in Bhimashankar Wildlife Sanctuary in 2011 and several patches in Sanjay Gandhi National Park in 2015. Every year Karvy undergoes sporadic flowering, but it is highly localised and not as significant as the periodic cycle of its masting.
|The dense undergrowth of Topli Karvy (Strobilanthes sessilis) photographed on top of Sindola fort in|
northern Western Ghats. August 2012.
Does it do it to protect itself from predation? Maybe, since the climate here is mostly hot and humid, not only are herbivores active throughout the year (I found the caterpillar of Southern Blue Oakleaf butterfly on a Karvy leaf in December of 2012), but infection by fungus and decomposition also threaten the tiny seeds of Karvy. Maybe the seeds of Karvy are too weak to support the initial growth of the sapling – and hence it is viviparous – and hence, periodic masting is more resourceful than yearly.
|The adult (top) and the caterpillar (bottom) of Southern Blue Oakleaf, Kallima horsfieldii.|
This butterfly is commonly seen in Karvy groves, and is its host plant. The
caterpillar was photographed on this Karvy leaf in December 2012.
Most studies on monocarpic plietesial plants have focused only around the plants – their relationship with the outer world has always looked at how it affected them, and not on how they affected it. Karvy probably affects others as much as its traits affects itself – and this is clear from the way it flowers in a peculiar colour.
Whenever I go on a nature walk, I make note of the colours of flowers, besides seeing insects and birds. These colours speak a lot about plants without them having to actually speak. The colours of wild species of flora are a result of a long evolutionary marathon – the flowering plants have been competing with one another for millions of years to attract something, or someone – besides looking pretty. Some have gone to the length of producing the most ethereal scents. They all call out to someone to, in literal sense, come to them. You know what I’m talking about: pollination. In the long evolutionary marathon, some created their own rules: some wanted to chase the wind, and they developed flowers with hanging anthers which, when shaken by the wind, carried themselves to land on the stigma of another flower, and came to be called anemophilous. Some chose insects as carriers, and came to be called entomophilous. Some preferred vertebrates, and came to be called zoophilus, of those who specialised with birds are called ornithophilous, and so on. Some removed themselves from the marathon and became self pollinated. Those that came to be pollinated by animals further led the race.
Colours are as important for flowers as signals are at crossroads, perhaps the metaphor is least poetic, but it is also a matter of life-and-death. The most common colours developed on the pollinator’s sense of vision. Birds, being sensitive to lights between green and red, are attracted to bright colours such as shades of red, and most bird-dependent plants bore those colours to attract them: Butea monosperma, Bombax ceiba, Woodfordia fructicosa, Helicteres isora – to name of few, are visited by many birds during their flowering season. [Read about the Palash tree I sat under for more]. It is yet not clear how the variation in colour affects birds: are they more attracted to Bombax ceiba for its crimson red – and voluptuousness – or are they more attracted to the flaming orange of Butea monosperma, do they get a better reward from B. ceiba or from Butea monosperma, we do not know.
|A resin bee collecting pollen and also depositing some on the stigma of Abelmoschus flower.|
In case of plants that became entomophilous, they developed in various shades of reds, yellows, and whites, and increasingly in the shades of violet. (I will be calling it violet or shades of, because getting into the complexity of purple-violet is beyond us; our eyes see purple and violet shades as one, and our computer screens show something else altogether). Most plants bear flowers with a little bit of violet mixed in, which can look purple or light pink, depending upon the shade, or mixed with whites and yellows. This is where things become interesting.
|The flowers of Ceropegia vincaefolia, photographed in 2014 on a young Karvy in Sanjay Gandhi National Park,|
act as traps for insects - their purple modified petals guide the insects inside where they remain
trapped until the flower is pollinated.
A study by Raine and Chittka (2007) showed that inexperienced bees showed “strong innate colour biases” to violet flowers. In their study the violet flowers were also most productive in providing the bees with nectar, whereas the blue flowers were less visited but they were also less productive. The authors conclude that “it is easy to imagine how strong innate colour preferences help guide naïve bees to find flowers on their first foraging trip away from the nest, as very few objects except flowers fall within the blue-violet colour range in a natural landscape”. The study tells us two things: they are attracted to flowers with violet shades more easily than others since they offered more rewards, which is why the plants adopted the shades of violet (or at least a little bit of it, in the form of varying concentrations of the anthocyanin pigment which gives several shades of red, purple, or blue depending upon the pH (read more here)) – this basically increased their chances of getting pollinated. Second, the violet colour developed merely to attract insects since most insects can see in UV, and weren’t more productive in terms of providing nectar and pollen to insects compared to the yellow or red flowers.
The case of Strobilanthes is that all the flowers of the three species fall in the shades of violet – some appear purple and some blue, but their colour is their ticket, whether they award the pollinator with pollen or nectar is a question we will answer shortly. I don’t think that after eight years, and, if we consider that on an average a worker bee lives for at least ten months, and a fly at least one month, which add up to 10 and 97 generations, respectively, they will remember Karvy’s blossoms. This may mean that insects, in some instances, are not innately attuned to follow a specific set of coloured flowers, it is not genetically programmed in them, but are attracted to the colour of the flowers because it shows up more brilliantly than other colours. The colour visuals signal them to come hither, and taste what’s on offer, because they stand out on in their UV spectrum. What if Strobilanthes petals were yellow? Yellow is a common colour in entomophilous plants, but I think it will then have to do with the award the yellow ones give – is it comparable to the award given by violet ones? In September, on the day we saw Karvy, there were 11 other plants with flowers: seven of them were in shades of violet, one was red, one white, and two yellow – of the two yellow one had a predominantly deep purple base of the petals.
|This is a representative list of flowers in bloom alongside Karvy.|
The predominance of flowers with violet-shade could only mean two things: violet flowers were rewarding than other coloured flowers, and hence was adopted by more species, or that they were less rewarding and hence were more eager to advertise the most easily perceptible colour to the UV-eyed insects.
|An ant tumbles out of a Karvy flower as two more explore its insides. Photographed in August 2008.|
What Strobilanthes tells us that they are quite rewarding – it might have to do with their gregarious flowering – but soon after the flowering season, the tribal peoples harvest the Karvy honey collected by the bees and is said to be quite expensive and tasty – this could be the measure of a good reward. The colour and the reward, both together, or either of the one, have made these species successful in attracting a large horde of insects to pollinate them, and get fertilized en masse in return, this has helped this group of plants of a long life in spite of reproducing only once every eight years.
|A Lauxaniid fly laps up the anthers of Karvy as a very small crab spider lies in wait. September 2016.|
Naturally, adorning an attractive colour and providing copious amounts of nectar and pollen will act like magnet. The insects feed on Karvy flowers in frenzy. I’ve seen flies in the family Syrphidae, Calliphoridae and Lauxaniidae, stingless bees, carpenter bees, and Indian honeybees (Apis dorsata) in the family Apidae, ants such as Paratrechina longicornis and Camponotus sp., and butterflies like Common Jezebel and Common Wanderer in the family Nymphalidae, and leaf beetles in the family Chrysomelidae positively feeding on Karvy flowers. I say positively, meaning they feed on pollen and nectar which is a positive sign that they also transfer it on to other flowers when they go around feeding. Even species of blister beetles (Mylabris sp.) munch on the petals of Karvy, although I am not sure if they do pollinate – here the strategy of mass grouping, exactly the way the deer herd together, must be at work.
|A stingless bee cleans itself before taking off from the petal of Karvy after exploring its insides. September 2016.|
Karvy’s pollination is not studied, but it is confirmed that Karvy is entomophilous. There are studies on its cousin S. kunthianus. Sharma and Kuriakose et al (2008) recorded Apis cerana indica as the major pollinator of this plant that flowers once in 12 years. Mohandass and Davidar (2014) showed Oriental White Eye as one of the [potential] pollinators as well. Anitha and Prasad (2007) quoting Matthew, said that bees such as Apis dorsata and A. cerana indica migrated whenever S. consanguinea was in mass bloom “to concentrate on its flowers for food”. If insects migrated for this purpose, what effect did Karvy flowering have on their lives? Just the way human population increased with an increase in food production, it is only natural to assume that their population would swell as well. This fact, although hard to measure, will be seen only in the next generation – mostly in October itself, or March, or the next onset of monsoon. Increase in population could also hint at an increase in diversity. And, if I stretch it further a bit, a good year for the birds as well. Generally speaking, the year the Karvy flowers can be considered a good year for local biodiversity.
|A view from Sindola fort with the mountain on the left showing dark-green patch of Karvy mixed with lighter grasses.|
The insects then also have to cope with the sudden fall in food resources – the year following Karvy’s blossom must be tiresome for them since they must then have to spend more time foraging. Would they think that something is amiss, or come to understand the anomaly that happened in 2008 and repeated itself again in 2016? Although it is less likely that there will be any memory or genetic imprint of Karvy’s mass flowering on them since only one or two generations experience it after a gap of 10 to over 97 generations, the no-strings-attached strategy of – excuse the term – “using” one another for services is only quite well known to humans, and it seems that Karvy and its pollinators share a similar relationship. Most animal-plant relationships have evolved in tandem, over several generations of trials and errors – and here’s Karvy that has done something completely out-of-the-box.
In this instance, with the Karvy’s easy access to its pollen and nectar, and its strategic placement of stigma, the plant seems to have not only adopted a winning colour, but also a design which gives access to a number of insects which physically differ in their structure and feeding habits – some such as flies lap up, some such as butterflies use straws, some such as bees use a spatula, and ants just tumble in and out. This is unlike some flowers such as that of Lantana camara, an invasive to India whose flowers are accessible to those with a straw and a spatula and not those that like to lap it up. It is also unlike many orchids such as Vanda and Cottonia, which also use several shades of violet to attract bees. Both these plants have evolved over the years to depend mostly on insects using straws and spatulas. Karvy’s design is simplest to use and hence, probably, cost effective, allowing it to rest for eight years until the first-and-the-last massive bloom. In this instance, it is the plant that innately knows it will draw the insects to its UV conflagration.
|A shrine in Bhimashankar Wildlife Sanctuary with a spread of Karvy (dark green) at the foothills of a sacred grove.|
Next year, the scene will be different. As these plietesial plants die after eight years, they will soon decay and the new ones will rise from their ashes, like a phoenix, as will the questions that stump us.
Carine, M. A. and Scotland, R. W. 2002. Classification of Strobilanthinae (Acanthaceae): trying to classify the unclassifiable?. Taxon. 51(2). pp. 259-279
Singh, R. K. and Diwakar, P. G. 2007. Gregarious flowering of Strobilanthes callosus Nees in western ghats. Indian Journal of Forestry. 30(4). pp. 553-555
Kelly, D. 1994. The evolutionary ecology of mast seeding. TREE. 9(12). pp. 465-470
Raine, N. E. and Chittka, L. 2007. The adaptive significance of sensory bias in a foraging context: floral colour preferences in the bumble bee Bombus terrestris. Plos one. http://dx.doi.org/10.1371/journal.pone.0000556
Sharma, M. V., Kuriakose, G. and Shivanna, K. R. 2008. Reproductive strategies of Strobilanthes kunthianus, an endemic, semelparous species in the southern western ghats, India. Botanical Journal of the Linnean Society. 157. pp. 155-163
Mohandass, D. and Davidar, Priya. 2014. Pollination biology of Nilgirianthus wightianus (Nees) Bremek. (Acanthaceae) in Upper Bhavani, Nilgiri mountains, southern India. International Journal of Advanced Biological Research. 4(1). P. 48-51
Anitha, K. and Prasad, S. N. 2007. Mass flowering and pollinators of Strobilanthes consanguinea in the western ghats, south India. Current Science. 92(12). pp. 1680
Superb!! Though I understand very little of itReplyDelete