This winter, on my first trip back to India since I’ve begun writing this column, I spent some time in our garden just outside Delhi looking for plants and animals to write about here. In searching for unusual creatures, I almost didn’t notice one of the area’s most common plants — the Vasaka shrub. In fact, I’d have missed it altogether if it weren’t for a single white flower that caught my attention on a foggy morning otherwise devoid of brightness.

I began to read about Vasaka, and realised something odd about our knowledge of nature — very often, we seem to know a lot about a few interesting aspects of an organism, but almost nothing about other equally important facets of its life. In the case of Vasaka, we’ve known for ages that this plant has exceptional medicinal properties. Across the Indian subcontinent, parts of this plant have been used to treat conditions ranging from coughs to jaundice to dislocated shoulders. Even today, when our lives seem more distant from nature than ever before, you can buy capsules of Vasaka extract at the pharmacy. I think it’s fair to say that, over thousands of years, Vasaka has contributed substantially to human wellbeing and persistence.

But do we know much about the persistence of the Vasaka plant itself? Though plants face many of the same challenges that we animals do, plants’ inability to move means that their solutions to these challenges are radically different from ours. Consider reproduction, for instance. Being stationary means you can’t move around in search of a mate, so flowering plants have evolved to employ other natural forces — wind, water, bees, butterflies, bats, birds and more — to search in their stead. In this role, these forces are called ‘pollinators’ because they transfer pollen (tiny grains that are the plant equivalent of sperm) between individual plants.

Some plants embody the notion that there are many routes to love and procreation — they are visited by many different types of pollinators, at least a few of which will transfer the plant’s pollen to another plant of the same species. However, many of these pollinators will also visit other species’ flowers, and pollen transferred to the wrong species is wasted. Some plants are therefore pickier, and employ specialised pollinators who only visit flowers of a single plant species. These plants don’t waste as much pollen, but risk not getting pollinated at all.

So how can you tell how picky a flower is, or who pollinates a particular flower in the first place? What a flower looks like offers many clues as to the pollinators it attracts. Consider, for example, Heliconia plants from the West Indies. Their flowers are small, white, nectar-filled tubes, hardly showy at all. But these flowers are enclosed in bright red or yellow leaf-like structures called bracts, and a series of bracts arranged along a stem stands out like a beacon amid green leaves, especially to hummingbirds. The birds’ beaks fit neatly into the tube-shaped flowers, giving them exclusive access to the nectar rewards offered by the flowers in exchange for pollen transport.

But some Heliconia are even choosier. Two species of Heliconia on the island of St Lucia are both pollinated by a single species of hummingbird. However, one Heliconia has a flower shaped exactly like the beak of the male of this species, while the other Heliconia has a longer, more curved flower, a near-perfect fit with the beaks of female hummingbirds. Each Heliconia species is thus pollinated only by one sex of hummingbird — you can’t get much pickier than that!

Returning to the Vasaka flower I saw that winter morning — can we guess who might pollinate it? Everything about this flower points us towards bees. Bees find white flowers especially attractive, and will often use flat petals as a landing platform. The fine purple lines on this platform can guide bees to the pool of nectar at the centre of the flower. As the bee feeds on its payment, pollen is probably showered on it from above, ready to be ferried to the next flower.

But these associations between a flower’s colour or shape and its pollinators are far from perfect, and our guess about Vasaka’s bee pollination would need to be confirmed by actual observation. I was about to end this essay with just a guess — my search for scientific studies on Vasaka had yielded plenty of fascinating information about how we humans have used this plant for our own benefit but almost nothing about how the plant itself persists. Then, in a final effort at combing through the literature this morning, I unearthed some research about this plant’s pollinators! I scrolled through the article somewhat nervously, but stopped with satisfaction at a photo of a carpenter bee fitting neatly into a Vasaka flower, its back dusted with pollen.

(Ambika Kamath studies organismic evolutionary biology at Harvard University)

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