My friend just wrote with the follow inquiry regarding her place cards:
"I don't want to go to the expense of having something calligraphed, and the standard folded cards feel kind of formal for the reception I think we'll wind up having. I thought for a while about having the cards somehow attached to tree branches, but I don't want to make it hard for people to actually pick up their cards either. Have you seen anything sort of casual and/or sort of plant-themed that you might recommend for a project?"
Here are my thoughts:

I adore #1 because all you would need to do is buy a stamp set of the alphabet (
like this one for $15) and stamp directly onto leaves you have collected outside. The rest of the options don't necessarily need a calligrapher, just someone with nice handwriting. It is difficult to write on the thin, flaky surface so you might need to collect extras incase you make a mistake.
#4 is also nice if you have darker colored leaves.
This white gel for pen @ $3.25 should work nicely.
*just make sure all your leaves are clean and dry before starting.

A wood element could also work, but you need to have access to nature & a hand saw (something I could not pull off in the city). If you did, you could use the same stamp set from above for the names. #2 is from Etsy
(here) and PS. there are SO many of these on for sale if you would rather purchase them, see
here. Another idea that could work is to buy some woodgrain embossed paper (see credit 3) and simply cut & fold the cards yourself. This is a good way to make the standard folded cards a little more special (and fit with the nature theme). Just make sure you don't buy real wood veneer, as it could crack when you fold it.
credits:
leaves: 1, 2, 3, 4, 5