How many letters does the top answer for “a tree of the genus fagus.” have?

The most common answer is beech (5 letters).

Crossword clue: a tree of the genus fagus.

1 answer found in Letterora's clue database (Wikidata facts, Open Trivia DB, WordNet and Webster definitions — all licensed sources).

beech 5 letters web-def

any of several large deciduous trees with rounded spreading crowns and smooth grey bark and small sweet edible triangula

a genus of fossil trees. 50% similar → ulodendron

a genus of trees; the plane tree. 50% similar → platanus

a tree of the genus eucalyptus 50% similar → eucalypt