This Activity is meant for Boy Scouts.

pencil and paper to keep score

Emphasizes leaf identification and speed to recognize and match items.
It would be good to have a presentation or training about trees before this activity.

Give all patrols 5 minutes to gather a single leaf from as many different trees as they can. Emphasize that their entire patrol needs to be back when the 5 minutes is up or they will lose points for every second they are late.

When scouts have returned, arrange patrols in a large circle, providing a place for each of them to organize their leaf collections. Make sure there is plenty of space between patrols.

Starting with the patrol with the lowest rank scout, one of their leafs is held up and identified. That patrol receives 10 points.
The first scout on another patrol that holds up the same kind of leaf receives 6 points for his team. The second patrol to hold up the same kind receives 4 points.
Whichever scout held up the first matching leaf gets to pick a leaf from his patrol's collection, hold it up and identify it.
The competition continues in this manner.

If a leaf is held up and incorrectly identified, the patrol receives no points, but the first patrol to hold up and correctly identify the same leaf in their collection receives the 10 points. 6 points and 4 points can be awarded to the next two patrols that have the same leaf.

If a patrol holds up and correctly identifies a leaf that no other patrol has, they receive their 10 points and get to go again.

When a patrol runs out of leafs, the turn passes around the circle until all patrols are out of leafs. This gives more points to those that have a wide range of leaf types that they can identify.

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You may add a rule that only the patrol leader can hold up and identify leafs. This makes patrols talk together more and uses the patrol hierarchy more.

You may emphasize that only leafs and needles from plants with woody trunks are allowed. No flowers, weeds, or grasses. Or, expand the scope and include those items if you prefer.