Erik Acharius (1757–1819) is widely regarded as the "Father of Lichenology." A Swedish botanist and student of Carl Linnaeus, Acharius was the first to systematically study lichens as a distinct group of organisms.

His major contributions include:

• Formalizing lichen taxonomy: Acharius applied Linnaean principles to classify lichens, creating a more organized and scientific approach to their identification and naming.
  
  

• Publishing foundational works: He authored several key texts, including Lichenographia Universalis (1810), which described hundreds of lichen species and laid the groundwork for modern lichen classification.
  
  

• Defining genera and species: Many lichen genera and species were first validly described by him, and his classifications are still referenced today.
  
  

Acharius’s meticulous observations and dedication helped establish lichenology as a legitimate scientific discipline. In recognition of his contributions, the lichen genus Achariusia and the Acharius Medal (awarded by the International Association for Lichenology) were named in his honor.

Simon Schwendener (1829–1919) was a pioneering Swiss botanist whose most significant contribution to lichenology was the revolutionary dual hypothesis of lichens. In 1867, he proposed that lichens are not single organisms but symbiotic associations between a fungus (mycobiont) and an alga or cyanobacterium (photobiont). This idea was initially controversial and faced strong opposition from many botanists of his time, who believed lichens to be autonomous plants.

However, Schwendener's theory, backed by microscopic observations, eventually laid the foundation for the modern understanding of lichens as mutualistic symbioses. His work fundamentally transformed lichen taxonomy and ecology, influencing generations of scientists. Today, his dual hypothesis is widely accepted and considered one of the most important milestones in the history of lichenology.