British Museum and Antarctic exploration In the mid-1930s, the department of botany at the
British Museum (Natural History) in London established three new assistant keeper positions. Mackenzie was appointed to the first of these roles, specifically for
lichen research, on 14 January 1935. She was mentored by lichenologist
Annie Lorrain Smith, who had recently retired. Mackenzie became especially interested in the lichen flora of the Antarctic, as it was comparatively unknown, and she began studying early British, French, and Belgian Antarctic collections in Turkey and Paris. She earned her
Doctor of Science from Edinburgh University in 1942, with a thesis titled "A monograph of the lichen genus
Placopsis". Mackenzie, a
conscientious objector, remained employed at the museum until 20 September 1943. During this time, she produced
monographs on the lichen genera
Neuropogon and
Placopsis, focussing in both on their Antarctic species. Through this work, she connected with
James Marr, a biologist from the
Discovery Investigations. Marr later led
Operation Tabarin, a convert mission instigated by
Winston Churchill during the
Second World War. This expedition aimed to reinforce British
territorial claims in the
Antarctic Peninsula, countering Argentine and Chilean claims, by establishing permanent bases and conducting scientific research. Further, there were concerns about the potential use of the Antarctic and sub-Antarctic regions by enemy
warships and
submarines. By establishing a presence in the region, the British could better monitor any naval activity and potentially disrupt enemy operations. Marr recruited Mackenzie to serve as the expedition's botanist. Mackenzie joined the crew in 1943 at Base A in Port Lockroy, where she was tasked with both botanical and geological collecting. At the island, Mackenzie participated in several short
manhauling expeditions, involving the manual transportation of two
Nansen sleds, each carrying of food and scientific equipment. In 1945, the team introduced twenty-five
huskies from
Labrador Canada, to bolster
sledding operations. These
sled dogs enabled more extensive surveying and exploratory journeys. Mackenzie was a member of the sledding team that navigated the
Prince Gustav Channel along the eastern coast of the
Graham Land peninsula, and later ventured eastward along the southern edge of
James Ross Island, eventually rounding its easternmost point before making their way northwest back to
Hope Bay. On one of these sledding expeditions, Mackenzie and a colleague chanced upon
Otto Nordenskjöld's hut on
Snow Hill Island, a relic untouched for more than four decades since the
Swedish Antarctic Expedition of 1901–1903. of
Buellia russa var. cycloplaca from
Trinity Peninsula; collected by Mackenzie in 1945 Mackenzie collected lichen samples and conducted experiments on the accumulation of snow and subsequent thawing. Among her discoveries was the permanently submerged
marine lichen,
Verrucaria serpuloides. During her stay from February 1944 to January 1946 in the Antarctic, Mackenzie documented a collection of 1,030 botanical specimens, with a significant portion personally collected by her. This collection encompassed lichens,
bryophytes, different types of
algae,
seed plants,
fungi, and
diatoms. The majority of these collections were made around the bases at Port Lockroy and Hope Bay, though she also sourced specimens from nearby excursions and during three extensive sled journeys covering approximately . Mackenzie determined the
genus of every lichen specimen, discovering some previously unrecorded in the Antarctic or unique to the Graham Land region.
Post-war academia and research After the war, Mackenzie became professor of cryptogamic botany at
National University of Tucumán. Her wife had developed severe
arthritis, and Mackenzie thought the warm Argentinian climate would help alleviate this. She traveled extensively in Argentina and Brazil to collect
Stereocaulon and marine algae samples. An unfortunate professional incident was shared by a family acquaintance who was assisting in the transportation of Mackenzie, returning from having spent several weeks collecting specimens in the mountains on horseback. As Mackenzie, the driver, and her family descended from the mountains, the shaking of the truck combined with a powerful wind caused the entire stack of collected specimens, along with their valuable annotations, to be irretrievably lost. In 1950, Mackenzie was put into contact with
Erling Porsild, who hired her as a
cryptogamic botanist at the
National Museum of Canada in
Ottawa. After the move to Canada, Mackenzie sold her private herbarium of 3,200 specimens to the
Canadian Museum of Nature. She continued to collect, gathering specimens from various locations in Canada, including the
Rocky Mountains,
Cypress Hills (
Saskatchewan),
Newfoundland,
Cape Breton Island (
Nova Scotia), and the
Ottawa area. In 1953, Mackenzie was offered the directorship of the
Farlow Herbarium of Cryptogamic Botany by
Harvard University, and she left Canada. Mackenzie met
Vernon Ahmadjian in 1955 when they both took a
marine botany course at the
Marine Biological Laboratory in
Woods Hole, Massachusetts. Their shared passion for lichens led to Ahmadjian enrolling as Mackenzie's first graduate student at Harvard the following year.
Antarctic return and other research endeavours In 1960, Mackenzie became a US citizen. A year later, she travelled to the
McMurdo Sound in Antarctica on behalf of the
National Science Foundation. During this visit, under
Operation Deep Freeze (codename for a series of United States missions to Antarctica), she observed the region's biological facilities and research. In 1963, she published the
Index Nominum Lichenum, a catalogue that she had compiled between 1932 and 1960. It encompassed all lichen
taxa names introduced during that span. Her work built upon
Alexander Zahlbruckner's foundational
Catalogus lichenum universalis. Mackenzie returned to Antarctica for a third time in October 1964, where she undertook
scuba diving investigations with her colleagues from France and Argentina, under a grant from the National Science Foundation and with the logistic support of the
Argentine Navy. This study, to which Mackenzie referred to as "Operation Gooseflesh", took part in the
South Shetland and
Melchior Islands. During her stay, Mackenzie collected
Verrucaria serpuloides, which she had previously discovered in 1944. She was awarded a US polar medal for her work. After Mackenzie left in 1965,
Denis Christopher Lindsay of the
British Antarctic Survey continued her surveys on the South Shetland Islands. Over the next three years, Mackenzie continued to collect specimens throughout Europe and Mexico.
Professional relations During the mid-20th century, Mackenzie and
Carroll William Dodge were among the leading figures studying Antarctic lichens. Both made significant contributions to the field, with Dodge focusing on preparing a comprehensive flora for the Antarctic continent and Mackenzie examining the lichens of the Antarctic Peninsula and nearby islands. Mackenzie had an adversarial rivalry with Dodge, criticising him for what she saw as "reckless taxonomy". She ceased her research on Antarctic lichens in 1969 upon learning that Dodge was on the verge of publishing his own account of them. Furthermore, when reviewing Dodge's 1973 publication,
Lichen Flora of the Antarctic Continent and Adjacent Islands, she dismissed it for what she described as its dubious scholarship. Other scientists have since corroborated Mackenzie's position. ==Personal life==