Beyond the call of duty!


Text Paolo Candotti Photographs Lesley Henderson


“Going far beyond that call of duty, doing more than others expect, this is what excellence is all about! And it comes from striving, maintaining the highest standards, looking after the smallest detail, and going the extra mile. Excellence means doing your very best. In everything! In every way.”



It’s a war

Like a stealthy army, invasive alien plants (IAPs), sneak up on you and before you know it, they are everywhere, sucking up the scarce water, intensifying wildfires, proliferating profusely and dealing a death blow to much of South Africa’s indigenous flora and fauna. At times imported unintentionally but often ostensibly for commercial/horticultural reasons these invaders cost South Africa many hundreds of millions annually in lost agricultural productivity, lost ecosystem services and on the efforts to control them.

South Africa has a long history of combating invasive species dating back to 1860 when Xanthium spinosum or “boetebossie” (the bush for which one is fined) became the first proclaimed weed in what was then the Orange Free State. A more well-known battle which put South Africa on the international biocontrol map was the successful use of the cochineal insects and the prickly pear moth in the early 1900’s to combat Opuntia ficus-indica or “prickly pear” across large parts of the country. The war took on a more formal and legislative approach with promulgation of the Conservation of Agricultural Resources Act (CARA) in 1983. All these efforts were however driven primarily by a need to protect agriculture. In 1995 the Working for Water programme was started which has made a massive contribution to clearing IAPs particularly in river catchments but it was only with the advent of the National Environmental Management: Biodiversity Act (NEM:BA) of 2004 that the broader issue of the impact of invasive alien species on our biodiversity was formally acknowledged in legislation.

Getting environmental legislation on IAPs drafted and promulgated is a very long and bureaucratic process handled mainly by senior managers in the Department of Environmental Affairs* but behind the scenes, scores of scientists work tirelessly for many years to build a solid scientific case. One of these scientists is Lesley Henderson who for the past 40 years has made it her life’s work to identify, assess, record and publicise the spread and impact of IAPs in South Africa.

Formative years

Born and raised in Benoni Lesley graduated from the University of the Witwatersrand with a BSc Honours in Botany, specialising in Plant Ecology. However, plants were not her first choice of study. Like many young people of her generation, holidays were spent in the Kruger National Park as well as on the verdant Natal South Coast both providing fertile ground for inculcating a love for nature.

Encouraged by her parents she nurtured her love for nature and developed a sincere passion for our rich biodiversity. Her older brother Ted, who became a Geologist but with a passion for the natural world, was a strong influence in guiding her choice of career. Whilst nature was an all-embracing interest, Lesley developed a particular love for the cat family which has remained with her to this day and her first choice of study was Zoology. In Lesley’s words “animals speak to you better than plants!”

However, when considering her options for employment, botany seemed to offer better prospects, especially as a female. In the 1970s field work, especially relating to wild animals, was generally regarded as work reserved for males. She experienced this prejudice firsthand when attempting to apply for a job in 1979 in the Kruger Park. Her interviewer, the senior ranger who was also in charge of scientific services, laughed at the thought of employing a female zoologist or for that matter, a female plant ecologist!

The Pretoria National Herbarium

A sideline task becomes mainstream

Lesley started her working career with the Botanical Research Institute (BRI) and was based at the Pretoria National Herbarium where she has been stationed for her entire career. Not one to be office bound, her work has taken Lesley to every imaginable corner of South Africa and beyond. Her first assignment was to study barrier plants – indigenous plants which could be used for security and other hedging, screens and windbreaks. This necessitated a fair amount of travel and during 1979 her inspirational mentor and boss at the time, Mike Wells suggested that she record invasive species that she noted along the roadside during the trips as a way of making the trips more productive.

Mike was the head of the Economic Botany Unit, but his portfolio included monitoring “problem plants” and especially introduced weeds. What was meant to be a “side-line” eventually morphed in 1994 into what arguably has been the most impactful and consistent work on invasive species in South Africa, the Southern African Plant Invaders Atlas (SAPIA). Lesley’s work on SAPIA has been greatly augmented by the recent publication of her outstanding new book “Invasive alien plants of South Africa”** which replaces her 2001 seminal work “Alien weeds and invasive plants”.

Lesley’s new book

The road travelled however has been long (literally over 150 000 km on road surveys alone), educational, exciting, dangerous, adventurous and above all highly rewarding from a job satisfaction perspective. Two early educational trips with John Anderson also from the BRI gave Lesley the basic knowledge and tools on atlasing, how to read maps and how to correctly collect and record data and set the basis for the work that was to follow.

Lesley on a Pompom weed survey – 2004

Science at the forefront

During our interview Lesley explained the early roadside surveys:

“Mike Wells got Kathy Musil (nee Duggan) and I to design a method of recording IAPs and do a survey of the central Transvaal (PWV area – Pretoria, Witwatersrand, Vereeniging). This survey resulted in my first publication on IAPs (Wells, M.J., Duggan, K.J. & Henderson, L. 1980. Woody plant invaders of the central Transvaal. Proceedings of the third National Weeds Conference of South Africa, 1979). After this Kathy and I extended the recordings to the rest of the Transvaal, while engaged in our other projects.

Kathy was transferred to Kirstenbosch in 1985 and thereafter I continued the surveys starting with Natal, followed by Free State and all the other provinces until completion in 1992. Pitta Joffe (author of a number of books on indigenous gardening) was my major assistant, who did all the driving while I navigated and recorded.”

Fountain Grass (Pennisetum setaceum) in the Wolwefontein area, 2008

The work was scientific, fact-based and methodical and Lesley was part of a broad network of scientists documenting the relentless march of IAPs.

IAPs are not a uniquely South African problem as they are causing havoc to biodiversity across the globe so Lesley’s network not only included many South African scientists and organisations but also extended to colleagues involved in weed science/invasion biology attached to universities and herbaria in countries across the world e.g. the team of scientists involved in the GLONAF (Global Naturalized Alien Flora) Database and invasive plants in Mediterranean Ecosystems of the world; African countries such as Zimbabwe – Mark Hyde, Namibia – Barbara Curtis, Swaziland – Kate Braun, Lesotho – S Talukdar, Kenya – Arné Witt; Australia – John Hosking, Rod Randall (Global Compendium of Weeds), Sandy Lloyd; UK – Kew Herbarium, Argentina – Roberto Kiesling (cacti).

Lesley pressing a herbarium specimen, January 2008

The war on IAPs was not without its detractors mainly driven by commercial interest with strong profit motives. Wattle, forestry and horticultural industries which focused on making profits without taking responsibility for the increasing problem caused by IAPs put obstacles in the way of many programmes including the finalisation of legislation. The Wattle industry initially was very opposed to any attempts to control the invasive acacias using biological control and threatened litigation if their plants were harmed in any way. However, increasing pressure from the national departments with scientific backing eventually got them to agree to the release of seed-feeding beetles and in later years other agents.

The South African Nursery Association (SANA), to its credit, has cooperated with government in the listing of invasive plants under NEM:BA and the removal of many ornamentals from their outlets. However, the controversial exemption of many so-called sterile cultivars has yet to be resolved.

Not unexpectedly, herbicide companies jumped on the bandwagon at the opportunity to make profits by supporting efforts to control IAPs.

South African Association of Botanists Silver medal and certificate

Formal recognition of Lesley’s work came when she received the Southern African Weed Science Society (SAWSS) Dave Annecke Research Award in 1998. In January 2017 she was awarded the South African Association of Botanists (SAAB) Silver Medal largely for the development of the SAPIA database.

There is little doubt that the impact of SAPIA and its related work has been a major tool in the war on IAPs and has provided crucial data on plant invasions for scientific studies and practitioners on the ground both nationally and internationally.

Camping in the desolate but spectacular Richtersveld, 1992

Challenges “on the road”

The scientific part of her work was something for which Lesley was well trained and prepared for but the practicalities of getting the job done posed many challenges. Lesley explained:

“All trips in the early years (1980s) involved mainly camping. We usually stayed in municipal caravan parks or anywhere we could just pull off the road. We slept in the vehicle or next to the vehicle either in a tent or simply in the open. We carried all our own water, food and cooking utensils. On the very first trip I did with John Anderson to the then northern Transvaal we slept under a different indigenous tree on each night. One night it was my job to cook freshly collected Mopani worms for supper!

Camping under a palm tree in Limpopo – 1979

I also did a trip with Lyn Fish (nee Smook) to the far northern Transvaal. On both this trip and the trip with John Anderson we were investigated by the security police/army who were patrolling the border with Botswana and Zimbabwe. On both occasions we had bright lights shone on us at night in our make-shift campsites. After some interrogation they realised that we were harmless! And unarmed!”

Camping in the NW Transvaal, 1982

In those early years there were no cellphones or GPSs so all navigation was done by maps – topographical maps in combination with AA road maps.”

Despite the well thought out planning that went into each trip they were not without their mishaps or amusing twists! Lesley recalled some such occasions:

“Sometimes minor roads deteriorated very badly and almost petered out between farms. On one occasion the road ended at a farm gate. A farm worker dutifully opened the gate, we drove in but realised that we were in an animal kraal and there was no way out. The farm worker then opened the gate for us again and we left, waving goodbye. I don’t know what he must have thought. “

Sometimes the work was more frightening. While doing a weed survey in Tembe, in northern KwaZulu Natal she was accompanied by a rather nervous game ranger who was armed with just a pepper spray against what are regarded by many as the largest elephants in Africa! Whilst at nearby Ndumo Lesley experienced a close brush with a crocodile. Lesley recounted her frightening experience: “My assistant Lin Besaans and I followed an overgrown pathway from a picnic site to the water’s edge to look out for any alien plants. We were startled by a sudden crashing through the undergrowth when a large crocodile fled ahead of us into the water.”

Ndumo fig forest – 2015

Sometimes Lesley and her colleagues would naively wander into high security areas.

“A few years ago, we were surveying along the Limpopo River. It was difficult to find an access road to the river. Eventually we found a minor road that led to an abandoned farm. We first surveyed the riverbank and, on our way out took a drive around the old house because that is where we were likely to find garden escapees. Behind the house we suddenly came upon a tent and a man in camouflage uniform scrambled out of the tent, with rifle in hand, and clearly very startled. My assistant, Lin Besaans, equally startled, said to the man “what are you doing here?” and he answered, “I am here to protect you!” Oh yeah, fast asleep in your tent? Then another man appeared, and we made a hasty departure.”

On other occasions she was pleasantly surprised and thankful at the help that she received while hunting for species or on the road such as the time she was rescued by a farmer when she ran out of petrol on the N1 highway near Hammanskraal at a time when there were no cell phones to call for help. Others were “roped in” unwittingly as Lesley explained:

“We were on a search not for an invasive species but for an indigenous plant that had the potential to be used as a security hedge plant. Euphorbia grandialata is restricted to the Olifants River Gorge in the Sekukunieland area of Limpopo. I was assisted by a young student Pierre van Eeden. We asked for directions in a small rural village. A young boy, probably about 12 years old was the only person who would speak to us and he said he could show us the way. He climbed into the vehicle and we set off on a long and winding route towards the Olifants River valley. We eventually found the plants we were looking for but realised that we would not be able to collect plants and make the return journey before nightfall. So, we spent the night in the valley, sharing our food with the boy. Pierre and I had a tent and the boy slept in the vehicle. Next day it took us a couple of hours to return the boy to his village and school. I wonder what story he told and who believed him?

Camping in the Olifants River valley – Early 1980s

That was just the first part of the story. Not long after returning the boy we had a breakdown. The gears seized and we could not budge the vehicle. Pierre set off walking down the road in search of some help. I was left with the vehicle and after some time I managed to wave down a vehicle which luckily was driven by someone who worked at Penge Mine which was the nearest place.

It turned out that the vehicle could not be fixed and was towed to Penge Mine. I spent the next two days there while Pierre hitch-hiked to Pietersburg. Government Garage at neither Pietersburg nor Nelspruit would come to our assistance. We eventually got a replacement bakkie. The kombi was railed back to Pretoria. The only reaction we received from anyone back home was that admin could not reconcile the logbook of the vehicle because the odometer had gone in reverse when it was towed! I remember writing a very cheeky letter of complaint about the unreliability of Government Garage vehicles to the Director. It didn’t help. We were stuck with GG vehicles for many years until we eventually could use our own fleet vehicles.”

View of the Ngorongoro Crater – November 2002

Beautiful places

One trip that Lesley looks back on very fondly was a trip to Ngorongoro Conservation Area in Tanzania. She was invited by Dr Pete Morkel, a vet from South Africa who had taken rhino to Ngorongoro and was spending about two years there to watch over their introduction. Dr Morkel’s house was situated on the crater rim and had a grandstand view of the ancient caldera spanning two hundred and sixty square kilometres: 20 kilometres wide and 600 meters deep. Today Ngorongoro shelters one of the most stunning wildlife havens on earth and Lesley thrived in nature’s bounty and all it offered. Lesley also surveyed areas outside of the crater and did one trip to the edge of the Serengeti plains. Being able to visit such a fabulous place was an experience all on its own made richer by the flexibility of working on the ground and being free to move wherever needed and observing the rushed tourists from a distance! She found more IAPs than Dr Morkel had thought of, so the trip was well received and was followed up by a visit by the head of alien plant control in Kruger Park, the late Wayne Lotter.

Whilst the trip to Ngorongoro was a once in a lifetime experience Lesley visited many strikingly beautiful places in South Africa in the course of her official duties which helped to further nurture her deep love for South Africa’s rich biodiversity. She has criss-crossed the country from the arid but breath-taking Richtersveld in the west to the lush forests and pans of Ndumo in the east. From the striking Kogelberg mountains in the south to the imposing mountains of the Waterberg in the north and all in between!

The Kogelberg mountains in the Western Cape – Oct 2009

Marakele National Park – December 2006

View of the Olifants River, Kruger National Park – February 2015

Court battle

Throughout her career Lesley has maintained a thoroughly rigorous scientific approach to all her work and this came in particularly useful when in 2013 the Kloof Conservancy called on her expert help. As mentioned earlier, formal recognition of the impact of IAPs came in 2004 with the promulgation of NEM:BA but this was toothless legislation without the accompanying regulations which, in terms of NEMBA should have been published by 31 August 2006. In early 2012 the regulations had still not been published and the Kloof Conservancy wrote to the then Minister of Environmental Affairs, the late Edna Molewa to ask when the regulations would be published and noting that in the meantime the detrimental effects of IAPs were continuing unabated. After repeated requests a reply was received in October 2012. Kloof Conservancy considered the reply from the Minister and concluded that it did not in any way dispel the concerns held by the conservancy that the problem of IAPs was not being adequately addressed by the authorities. Subsequently the conservancy led by Advocate Michael Smithers SC of the Durban Bar initiated High Court Proceedings against the minister and seven related government agencies to compel the Government to implement Invasive Alien Species (IAS) legislation.

One of the critical components of the case presented by the conservancy was the need to include expert opinion on the issues relating to the impact of IAPs. The conservancy initially approached two senior well known scientists, one within the DEA and one outside of government but contracted to do government work and who had been very vociferous and critical on the lack of action by government. Both declined to assist. The conservancy then reluctantly approached Lesley. The reluctance came about because whilst Lesley was already a renowned weed scientist her position within Agricultural Research Council (a government funded agency) made her vulnerable to possible official retaliation. After clearing the issue with her immediate supervisor Lesley provided the conservancy with a comprehensive affidavit explaining her opinions on the required points which was to become crucial evidence in the court case.

Judge Vahed of the Durban High Court heard the case on 25 April and reserved judgement. On Friday 1 August 2014 the Minister of Environmental Affairs issued a set of Regulations (GG37885) and a list of Invasive Alien Species (GG37886). Unlike previous versions which had no implementation date, these were scheduled to automatically come into effect on 1 October 2014. The publication of the Regulations and the list of Invasive Species pre-empted the judgement which was pending at that stage.

Judgment was delivered on 22 October 2014 and Judge Vahed ruled in favour of the Kloof Conservancy with punitive costs.***

When asked how she felt about being involved in the court case Lesley replied, “Initially I was reluctant to get involved because I didn’t know what was expected of me and the thought of having to appear in court was very daunting. After it was explained what was required, I felt better about the process and if I kept to the facts then I had nothing to fear.”

The Kloof Conservancy issued a press release on the day that the judgement was delivered. The press release included the following paragraph:

“Our special thanks go to Lesley Henderson, one of South Africa’s foremost weed scientists, and editor and compiler of SAPIA News, for her authoritative input and her personal and professional courage and integrity in deposing to expert evidence on affidavit. The judgment will stand as a permanent public record of her contribution to the case.”

This was certainly a case of a public official standing up for what she believed in and acting beyond the call of duty!

Looking ahead

As with all our interviews I asked Lesley about her thoughts for the future of our biodiversity and the prospects for the planet’s environment as a whole. Lesley remarked that one of her most disappointing experiences had been a return visit to Northern Kwa-Zulu Natal, an area that she had always enjoyed visiting, only to find severe environmental degradation, high levels of IAP infestations, uncontrolled housing expansion, overgrazing and litter everywhere. Sadly, but maybe realistically Lesley noted, “I am pessimistic about the future for the environment in both South Africa and the entire planet. Human population growth and consumption of natural resources are unsustainable and will ultimately lead to the destruction of much life on the planet.”

Her feelings on this issue are well summed up by a quote referred to:


“What is man without the beasts?

If all the beasts were gone,
man would die from great loneliness of spirit,
for whatever befalls the beasts, befalls also the man.
All things are connected.
Whatever befalls the Earth,
Befalls also the sons of the Earth.”



The launch of Centre for Biological Control at Rhodes University – November 2017

Photo source: CBC Newsletter Issue 1 November 2019

Lesley took early retirement on 31 March 2020 and with regard to future plans, she is still in the process of adjusting to the idea of having some free time available. She has always enjoyed her interactions with the scientists involved in biocontrol and considered them as one of the highlights and more enjoyable aspects of her career. Lesley commented, “I always looked forward to the annual biocontrol of weeds workshop. I attended the first meeting in 1987 and attended most of the meetings since then. Until recently I was the only non-biocontrol researcher who attended these meetings. I was absolutely fascinated by the work and felt so privileged to be a part of the biocontrol community”.

Over the years she has developed good relationships with many in the biocontrol field and some further collaboration might be an interesting possibility in the future.

Dr Stefan Neser and Dr Carina Cilliers, pioneers in biocontrol at the launch of Lesley’s 2001 book ‘Alien weeds and invasive plants’.

The one thing that we can be reasonably certain of is that Lesley will be spending as much time as possible at N’tsiri Private Nature Reserve, which is situated in the Greater Kruger Area. There she is planning to spend more time with her first passion, observing the leopards of N’tsiri while also enjoying bird watching, photography and of course keeping an eye out for invasive alien plants. We wish her well and salute a true member of the Eco-Impi.****

Leopard at N’tsiri Private Nature Reserve


*This department is currently operating as the Department of Environment, Forestry and Fisheries.

**The book can be sourced directly from ARC – contact:

***Dr Guy Preston led the DEA’s technical defense during the court case and has emphatically denied that the court case had any influence on the eventual publishing of the NEMBA regulations and added that the process was a serious waste of his department’s scarce resources. There is however reasonably general consensus amongst IAP practitioners both inside and outside of government that the court case forced the DEA’s hand to finally publish the regulations and helped break the political log-jam which had hampered progress.

****An Impi is defined as “an armed band of Zulu warriors involved in urban or rural conflict. In our context we refer to an Eco-Impi as those conservationists armed with knowledge and experience who are fighting to help protect our biodiversity and have made a significant impact in our area.