The minimum leaf number 
of a connected graph 
is the smallest number of tree leaves in any of its spanning trees. (The corresponding largest number of leaves is known as the maximum leaf number.)
A traceable graph on 2 or more vertices therefore has minimum leaf number 2.
See also
Maximum Leaf Number,
Spanning Tree,
Tree Leaf Explore with Wolfram|Alpha
References
Goedgebeur, J.; Ozeki, K.; van Cleemput, N.; and Wiener, G. "On the Minimum Leaf Number of Cubic Graphs." Disc. Math. 342, 3000-3005, 2019. Referenced on Wolfram|Alpha
Minimum Leaf Number Cite this as:
Weisstein, Eric W. "Minimum Leaf Number." From MathWorld--A Wolfram Resource. https://mathworld.wolfram.com/MinimumLeafNumber.html
Subject classifications
