Bartlett was an enthusiastic plant collector, who specialised in collecting New Zealand mosses, liverworts, and lichens. He was a self-taught amateur botanist, and began collecting plants when he was in his twenties. The speed at which he collected plants, and his capacity to cover large areas of unvisited country led him being given the nickname "Hurricane Bartlett". John spoke Māori, which at times may have helped him gain access to land not normally visited by botanists. He collected specimens for professional botanists. DSIR Botanist Tony Druce describes meeting and working with Bartlett: "He arrived at our home with his old car laden with plants... Of course he exhausted the field of higher plants in North Auckland in a few years, and moved on to lower plants. He went at such a speed that he could never give me precise localities". From the mid-1970s Bartlett began collecting lichens. He sent specimens to specialists around the world, and David Galloway, the New Zealand lichenologist, recalled that from 1977 to 1985 Bartlett provided him "with an apparently inexhaustible supply of new and critical material for the New Zealand lichen flora". An extract of a letter written by Bartlett to Galloway in January 1982 illustrates his indefategible approach
"... I have returned from the incredible wilds of the West Coast of the S.I. after spending a night in the bush on the coast near Bruce Baycut off from the beach by rising tide! falling into a tarn near the Percy Pass nearly stranded on a limestone bluff at Castle Hill, Cave Stream 50' below! Forgetting my boots and having to climb up through the bush above Wilmot Pass in my socks!..."
While searching for liverworts in 1975, Bartlett came across an unusual species of rātā growing at Radar Bush, 9.5 km south-east of Cape Reinga. His attention was drawn to the tree’s distinctive bark, which is spongy, whitish and flakes easily, but he was unable to reach any branches. He took bark fragments to Victoria University botanist John Dawson, who was unconvinced that the tree was unusual. Bartlett returned to the area with a rifle, with which he was able to shoot off a branch. It was ten years before its white flowers were seen by scientists in 1984, appearing ‘like snow over the tree crowns’ and allowing the new species to be formally described and named Metrosideros bartlettii, known as Bartlett's rātā, or rātā moehau in Māori. Bartlett's rātā is now grown as a garden plant, but only 13 adult Bartlett's rātā are known to still exist in the wild.
Eponymy
As well as Metrosideros bartlettii, numerous other taxa were named after Bartlett, including: