James R. Gracen
I personally play that the L/R have to come from the side of the trunk card, but I have met others who split the card in half (virtually!) and play that Left/Right is either side of the centre line. This is something your group needs to agree on before play begins.
The actual text on the card is...
Kodama card wrote:
Score 3 points for each card that can be traced back to the left side or right side of your trunk card, whichever is fewer.
Emphasis in bold is mine. So it does say left and right *side*, rather than left and right *half* of the card. I would be inclined to rule that you would only count the cards that trace back to the sides of your trunk card, not those that trace back to either half of the top of your trunk card.