
1) American plane 2) American sycamore 3) Plane tree 4) Platan 5) Platanus occidentalis 6) Sycamore
Found on
https://www.crosswordclues.com/clue/buttonwood

1) Sycamore
Found on
https://www.crosswordclues.com/clue/buttonwood

• (n.) The Platanus occidentalis, or American plane tree, a large tree, producing rough balls, from which it is named; -- called also buttonball tree, and, in some parts of the United States, sycamore. The California buttonwood is P. racemosa.
Found on
http://thinkexist.com/dictionary/meaning/buttonwood/
But'ton·wood` noun (Botany) The
Platanus occidentalis , or American plane tree, a large tree, producing rough balls, from which it is named; -- called also
buttonball tree , and, in some parts of the United States,
sycamore . The California buttonwood is
P. racemosa ...
Found on
http://www.encyclo.co.uk/webster/B/119

sycamore (def. 1).
Found on
https://www.infoplease.com/dictionary/buttonwood
No exact match found.