Balmy balsams

The endangered Impatiens, endemic to the upper Nilgiris, offers an excellent illustration of phytogeography.

TEXT & PHOTOGRAPHS BY TARUN CHHABRA

With tender heed Bringing thee chosen plants and blossoms blown Among the distant mountains - "A Farewell", William Wordsworth

THE upper Nilgiri plateau in the southern Western Ghats is characterised by its unique shola-grassland ecosystem - patches of stunted evergreen montane forests, nestled in the moist hollows of folds between hills, separated by undulating grassy downs and protected from wind and fire.

The Nilgiris is home to a number of endangered mammals such as the Nilgiri tahr and the Nilgiri marten. But it is in the abundance of flora that this global biodiversity hotspot enjoys a unique position in the entire Western Ghats.

A large number of what are basically Himalayan species such as rhododendron, lilium, ilex, geranium and berberis (even the tahr and the marten are essentially Himalayan species), are found in this small area. The other important fact is that 90-odd plant species and varieties, many of them undocumented and found nowhere else on the earth, are endemic to this region. Of these, the genera Strobilanthes and Impatiens (a genus of the annual flowering plants belonging to the Balsaminaceae family), are the most significant ones. Each of these is represented by around 35 species in the Nilgiris. Of them, Strobilanthes has six varieties and Impatiens a dozen.

In their ongoing study of wild balsams, researchers of the Edhkwehlynawd Botanical Refuge (EBR) of Udhagamandalam (Ooty) noticed that some of the native species had become rare. It took them three years to locate Impatiens denisonii; they made three annual field trips during August-September, when the balsams are in bloom, and reported the sighting of the species on the third such visit. It is likely that this was the first scientific collection of the species since British naturalist Richard Henry Beddome first documented it in 1862.

The genus Impatiens offers an excellent illustration of phytogeography, the geography of plant distribution in a particular region, here the upper Nilgiri plateau.

The Nilgiris was part of the ancient continent, Gondwanaland, which connected India with Africa, South America, Australia and Antarctica. The name Gondwana suggests the `forest of the Gonds' (of central India). During the early Cretaceous period, South America, Africa, Madagascar and India separated. The plant sub-order Geraniineae, which contains the Geraniaceae, Tropaeolaceae and Balsaminaceae families, is believed to have originated in west Gondwanaland in the last 60 million years or so. The far older parent stock of both Impatiens and Tropaeolum belonged to an unknown family in western Gondwanaland. This existed before the drifting away of South America from Africa a 100 million years before present. After the break-up of Gondwanaland, the common descendants of this parent stock evolved into Tropaeolaceae (of which the genus Tropaeolum is a constituent) and were restricted to South America, and Balsaminaceae with representations in Africa, India and Madagascar. Recent pollen studies have shown several similarities between these two genera to substantiate this theory.

It is now postulated that Balsaminaceae is as old as around 50 million years before present. After the continent split up, some migration of species - including that of Impatiens - is likely to have continued through various small islands and mid-ocean ridges for a considerable period of time. That is, until Africa, Madagascar (despite being comparatively close to the former most Impatiens species on this island are endemic) and the Indian subcontinent moved too far apart to allow cross-migration.

During the mid-Eocene era - approximately 45 million years before present - the drifting Indian subcontinent pushed against Asia. This phenomenal event led to the formation of the Himalayas. This Himalayan route was to lead much later to the migration of Impatiens into South-East Asia. Expectedly, the Impatiens genera of South-East Asia and the Himalayas are different from those found in South India, Africa and Madagascar. Some of the Impatiens species native to the Nilgiris such as I. munronii and I. jerdoniae are directly related to the African species.

Broadly, the genus can be divided into two major groups based on the shape of the fruit. The northerly group has long-linear fruit pods. Its members later migrated into Central Asia, Europe and, much more recently, North America. The late migration is the reason why these regions have a poor representation of this genus. The few species that managed to survive there were annuals that could adapt to colder climes. The southerly group, occurring in Africa, Madagascar, South India, Sri Lanka and some parts of South-East Asia (where the two groups overlap), have spindle-shaped (fusiform) fruit pods that are distinctly turgid in the middle. It is not at all surprising then, that 95 per cent of the Impatiens species of South India are endemic to the Western Ghats. Only one species, I. chinensis, is widespread in the Himalayas.

By the time the Himalayas were being formed during the Neogene era, the distinctive montane flora of the Western Ghats would already have been long isolated by the increasing drought conditions prevalent over the subcontinent. At this stage, Impatiens became isolated within the highland forest and grassland refuges in Africa, Madagascar, South India and Sri Lanka. Long periods of isolation in remote upland `islands' along with extended periods of intense drought in other parts of the Indian peninsula led to their evolution into distinct, endemic neo-species, a process that continues even today.

The Pleistocene Ice Age eras are thought to have decimated the existing Himalayan flora. By the time the Himalayan vegetation began to get re-colonised at the end of the Pleistocene era, the South Indian Impatiens would have been long isolated from the Himalayas by the vast dry lowlands of central India.

Impatiens, the true balsams, is one of the largest flowering plants - there are over 800 species worldwide. The generic name may sound peculiar until one sees how a ripe fruit pod tends to curl up inwards, and does so, so violently, that the seeds are expelled some distance away. Hence they are said to be `impatient' to propagate their seeds. These seeds might germinate at the new places or being light, may be carried much farther by wind. Erasmus Darwin, the great grandfather of Charles Darwin, had this to say about the genus:

"With fierce distracted eye Impatiens stands, Swells her pale cheeks and bran dishes her hands; With rage and hate the astonished groves alarms, And hurls her infants from her frantic arms."

It is also for the same reason that the only species native to Britain, I. noli-tangere, has its name derived from the Latin word for `touch-me-not'. This genus is distributed mainly in the Old World tropics, especially Africa, India and other parts of Asia. In India, there are just over 200 species and here too, their distribution is highly localised with the Himalayas and the Western Ghats being the main centres of speciation.

Balsams are also commonly referred to as `busy lizzies' owing to the explosive nature of their fruit pods. Of late, they have become common as pot and bedding plants and can be seen in many home gardens. However, this popularity is based on just a couple of species - I. walleriana and I. hawkeri. In India, the only species seen in lower altitudes is the attractive albeit highly variable I. balsamina, and this has wide distribution in Africa. One species endemic to western Nilgiris, I. orchioides, derives its name from its resemblance to orchids of some Liparis species.

The diversity in shape and colour of this genus has long fascinated botanists. With balsams rivalling orchids in their sheer beauty and bizarre form, it is surprising that they have not become popular. To anyone who has seen wild balsams in their natural habitat and intriguing forms and the vast areas that certain species carpet during the peak flowering season, it is apparent that these ancient plants are in no way inferior.

To a keen observer, the staggering diversity of form in balsams is most likely to be related to their often specific pollinators. The flat kind of flowering species not only mimic but attract butterflies. Similarly, some species that have `hooded' standard petals, allow specific pollinating bees and beetles in. The incredible bird-like forms are actually pollinated by birds. The most well known example is I. Niamniamensis, which is native to East Africa. This is popularly described as the `Congo cuckatoo' after the bird by the same name. Not surprisingly, the two Nilgiri species that are directly related to a common ancestor from Africa are also bird-shaped and pollinated.

The other unique feature of this genus is the unusually high degree of endemism. The existing Impatiens species of the Western Ghats forms a relict population. These species are restricted to montane forests and grasslands.

For this reason, most of the endemic species are found in very small areas and the few species such as I. balsamina that are able to grow at lower altitudes are widespread in their distribution.

Very few other regions in the world exhibit the degree of restricted endemism of Impatiens in a more pronounced manner than the upper Nilgiri plateau. Over a dozen species of Impatiens are found in the upper Nilgiris, in the 100-square-kilometre area around the Mukurti National Park. Many of these are often restricted to habitat ranges extending over a few adjacent hillsides. Nothing can confirm the development of the western upper Nilgiri plateau into an upland island and a major centre for plant speciation better than this example of Impatiens speciation. These endemics are often restricted to their own specialised habitat niches.

The Western Ghats (along with Sri Lanka) is home to an endemic group known as Scapigerae. These are the acaulescent, or `stem-less', balsams; the plants grow from scapes that emerge directly from tuberous roots. Many of the species endemic to the upper Nilgiris are also scapigerous - eight out of 12 such species found here are endemic to a small habitat. Undoubtedly, this is the largest concentration of species under this category. Although these are not truly epiphytic, many acaulescent balsam species are found on trees and/or rocks. This is because they do not have a specialised root system or phorophyte to anchor on to trees, unlike epiphytic orchids that possess such a system. But these balsams achieve this by anchoring on to a thick layer of moss adherent to tree or rock.

At least one rare Nilgiri endemic, I. neo-barnesii, is seen almost exclusively on tree trunks, but is still not termed as a true epiphyte. There is, however, a solitary example of a true epiphyte - I. jerdoniae in the Nilgiris. Here, the dorsal petal is small and hood-shaped and the lower sepal terminates into a striking bucciniform spur.

The scapigerous and other Impatiens varieties are annuals, with a short flowering cycle. Thus the root tubers remain in the moss or ground during the dry months. Most of the species found in the Western Ghats are hygrophytes - they grow in elevated areas that experience heavy, albeit seasonal, rainfall. Consequently, a large number of species are found on mossy rocks that are dripping wet all through the flowering season (after the southwest monsoon, especially in August-September).

Other species have found permanent niches on smaller rocks and stones that are constantly kept wet by the spray from adjacent streams and waterfalls. Therefore, one can view the flowering spectacle of this genus only after the cessation of the southwest monsoon.

As the surrounding areas are getting dry, the habitat of the endangered Impatiens has begun to shrink. Similarly, alteration of habitat from grassland to tea and exotic tree plantations has pushed many of these species to the brink.

Dr. Tarun Chabbra is the founder of Edhkwehlynawd Botanical Refuge and is based in Udhagamandalam (Ooty).