Tricholoma equestre also known as ¨The Man On Horse Back¨, was originally described by Linnaeus in 1753 in Species Plantarum Vol 2 as Agaricus equestris. As one can imagine ¨equestris¨, was derived from the Latin root word for horse or equestrian.

While it’s not exactly clear why Linnaeus chose this name, there are a handful of hypotheses. One of the most cited is that the mushroom caps are saddle-like in form. While it’s not obvious at first, these mushrooms do often have undulating margins that, under the right conditions, could be shaped like a saddle. Perhaps Linnaeus wasn’t specifically saying this mushroom looks like a saddle but perhaps just referring to the unevenly upturned cap margin that it often displays. Another but less convincing hypothesis is that it the mushroom looks like a man riding a horse. 

Another curious reason for this name was described in the 1810 book ¨Glossaire de botanique ou Dictionnaire étymologique de tous les noms et termes relatifs à cette science¨ (Glossary of Botany or Etymological Dictionary of All Names and Terms Related to This Science) that says the following passage ¨(An) agaric, whose cap opening in the shape of a star presents some resemblance to the decoration of a chivalric order.” Again, perhaps this is simply a reference to the undulating margin that could possibly be star-shaped.

Lastly, another theory suggests that equestris may be referencing to the wealthy, high ranking Knights. Thus this mushroom, due to its delicious flavor, was highly valued by the noble classes of Europe and was truly seen as a gourmet food. 

While there are many common names for this mushroom, many European names reference Knights or Equestrians. Whether these predated the naming by Linneaus isn’t clear in the records. It would make sense that Linnaeus didn´t fathom this name out of pure imagination but likely based it on an existing common name from Sweden, France, or another part of Europe.