Wildflowers by the wayside – are they weeds? [Commentary]

In the warmer parts of southern India are found many wayside herbs, and small shrubs, such as cat’s claw (Martynia), devil’s trumpet (Datura), touch-me-not (Mimosa), yellow alder (Turnera), periwinkle (Vinca) and several species of climbing morning glories (Ipomoea) that bear enchanting flowers.

None of these are however native.

These are species introduced during various times in history, beginning with the colonial era, as ornamental garden plants. These plants have escaped from gardens, and are widely naturalised. They are not only hardy but will quickly adapt and spread and hence they are often called ‘weed’.

Weeds, pioneers and invasives

No plant is biologically a weed. In its verb or noun form, the word ‘weed’ implies something unwanted and to be promptly removed. Thus, the word weed emerges as a purely management jargon loosely used in gardening, agriculture and forestry, for centuries, and more recently in landscaping and some misguided habitat restoration and environmental rejuvenation missions. Sadly, sometimes the word is even used by botanists to describe wayside herbs and shrubs. What many do not know is the fact that several of the so-called weeds are the primary larval host plants of common butterflies. A good example is the giant milkweed (Calotropis).

Wayside wild plants can either be pioneers or invasive. Pioneer is a term often used by ecologists in understanding the early stages in vegetation succession. When a habitat has undergone a disturbance due to fire, flooding or any other impact (including human), part of the natural vegetation is temporarily lost. The affected area is immediately colonised by some plants. Such plants are called pioneers and in most cases the species involved are annuals: plants that complete their life cycle within one growing season (although there are grasses, shrubs and small trees that can be pioneers). Initially the fresh growth or succession is very dense, but pioneers slowly make way for the recovery of the original vegetation if the habitat is left undisturbed. This pattern of succession is seen all over the world. Pioneers are therefore not weeds and should not be removed.

Invasives are altogether different. They are species that are at the same time adaptive, aggressive and persistent. They tend to modify the local habitat and ecosystem to better suit their needs. Lantana camara, introduced during the colonial era in India as an ornamental garden plant, has since become invasive and has been responsible for widespread degradation of wildlife habitats throughout India. Globally, it has cost governments huge sums of money in the century-old battle being waged against it. Lantana produces attractive flowers that are visited and pollinated by scores of insects including butterflies. The small fruits are edible and have become an important source of food to many species of birds and small mammals. Sometimes, even sloth bears are known to feed on the fruits. Thus, the alien species has developed mutualistic (mutually beneficial) associations with native insects, birds and other animals (mainly for pollination and seed dispersal) and has influenced local habitats and ecosystems to maximise its chances of survival. It is therefore worthy of being designated as an ‘invasive alien species’.

History of introduced wildflowers

Lantana is just one example. Hundreds of species of temperate wildflowers have been introduced in hill stations throughout the country. As most of these plants need bright sunlight, they quickly colonise areas where natural vegetation has been tampered with or destroyed. European colonists were also responsible for introducing invasive aquatic plants such as the water hyacinth. It was first introduced from tropical American wetlands all over the world to enrich garden ponds.

Tropical regions also have a great diversity of terrestrial wildflowers, and some of them, such as orchids, heliconias, wild gingers and turmeric and wild bananas, are extremely popular. Even trees like jacaranda, flame of the forest, gul mohur, copper pod, African tulip tree, Indian tulip tree, silk cotton, cannonball tree, and the many species of cassia are of tropical origin. All these are easy to propagate and are gardeners’ favourites everywhere. They commonly adorn urban parks and avenues, and need plenty of light to fully grow and blossom. Jacaranda, for instance, is an emergent tree in tropical American rainforests. In its natural habitat, it is a tall and majestic tree unlike its warped and stunted urban versions that we commonly see.

Many herbs and small shrubs that are most widely found and often described as wildflowers are those that have had their original homes elsewhere. Wildflowers of the temperate region, especially small herbs in the Alpine meadows, produce some of the most brilliant flowers. These are highly seasonal and the flowering is synchronised (as that in the famous Valley of Flowers National Park in Uttarakhand). There are two reasons for the highly seasonal and synchronised floral extravaganza of the Alpine meadows. First, is the limited availability of sunlight that the plants attempt to exploit. Second, is the intense competition for insects, the most important pollinators. The survival strategy of wildflowers in the region therefore is ‘produce the most resplendent flowers, and buy the best pollination service’. Day length plays a major role in the seasonal availability of sunshine and insect-pollinators in the temperate region and hence the synchronisation.

Captivating wildflowers have made many Alpine meadow herbs including primulas, irises, dianthus, saxifrages and others every plant-lover’s delight. They have been collected, acclimatised and transported all over the world, and even adorn tropical homes. Collection, acclimatisation and worldwide transport began early during the colonial era as Europeans who settled far and wide were rather inclined to creating miniature European landscapes around them. The British, in particular, created typically English landscapes throughout the Commonwealth by introducing plants. Their obsession with garden homes wherever they settled did not even spare the Guindy (National) Park of Chennai. Hill stations in the Western Ghats such as Ooty and Kodaikanal have been heavily invaded by some legacy wildflowers. According to botanists, there can be anywhere between 400 and 600 species of naturalised European plants, including wildflowers, in these ecologically fragile hill-towns.

Following the trail of light

Roadsides, railway tracks and other artificial conduits are very unstable as wildflower habitats. They are subject to various forms of human interference, the most common being ‘maintenance’. However, introduced wildflowers tend to choose and thrive in these unstable habitats. Depending on the topography and climate, the local wildflower species assemblage tends to change. In colder landscapes such as that in the higher parts of the Western Ghats and Western Himalayas, there is a predominance of European wildflowers. In lower elevations, which are warmer and drier, there are different species, including some introduced from other tropical countries, like Lantana.

The primary determinant is light. Unlike orchids, heliconias, wild gingers and turmeric that prefer shade or forest edges, wayside wildflowers are better adapted to open and well-lit spaces. That is why they also do well in window boxes and balconies and are not suitable as indoor plants. Many species do not need much watering. Yellow alder, for instance, grows profusely along roadsides and railway tracks in and around Chennai and elsewhere in southern India. The periwinkle is common along beaches. Both species can withstand a fair amount of heat and drought.

Wayside spaces not only provide opportunities for getting as much light as is needed without much competition in wildflowers, but may also help in seed dispersal. The seeds of the cat’s claw (Martynia sp.) for instance, are dispersed after they hook on to the bodies of passing livestock or the clothes of people. It is for this reason that the species is found close to roads and along well-lit trails. Periwinkle pods burst open to scatter the seeds and only those that fall in well-lit open soil sprout and grow. Morning glories (Ipomoea sp.) require support to climb and also bright light to thrive. And that should explain their partiality to railway tracks and the popular nickname ‘railway creeper’. Choice of habitats (and microhabitats) of a wildflower is thus determined by a combination of environmental and biological factors, irrespective of its country of origin.

The goat’s-foot vine (Ipomea pes-caprae) is a native beach plant found along Indian coasts. It may also be seen growing in sandy shores of rivers and wetlands. The trailing vines are excellent sand-binders preventing beach and shore erosion. Unfortunately, beach and wetland restoration enthusiasts remove this plant calling it ‘weed’. Not many know that it is one among the very few native morning glories that we commonly find. While it is not possible for everyone to empathise with wildflowers, there should at least be prudence in habitat restoration and some discretion before condemning plants as weeds.

Citation:

• Kehimkar, I. (2001) Common Indian Wildflowers. Oxford University Press & Bombay Natural History Society, Mumbai.
• Muthiah, S. (1987) Madras Discovered: A historical guide to looking around supplemented with tales of ‘Once Upon a City’. East-West Press, Madras.
• Savory, I. (1900) A Sportswoman in India: personal adventures and experiences of travel in known and unknown India. Hutchinson & Co., London & Philadelphia.
• Daniels, R J R and Vencatesan, J (2008) Western Ghats: Biodiversity, People, Conservation. Rupa & Co, New Delhi.

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Banner image: A tropical carpenter bee pollinates a giant milkweed flower. Image by Bernard Dupont via Wikimedia Commons (CC BY-SA 2.0).