Ooh a mystery! I can tell you that it's not chard, spinach, or a brassica. It'd be helpful to know where you're gardening at.

Also, sheep poo paper?! I think I need some of that.

I think the real problem here is in using native species (which could dilute genetic material of a different native population, as mentioned earlier), or in using species that might escape from gardens and invade natural areas. There are plenty of horticultural plants that are benign, and if these cards are going to be made and sent, they should be using plants that are clearly in that category. Unfortunately, it's often difficult to spot a potential invasion. There are some programs (I think there's one at the Chicago Botanic Garden) where researchers are starting to evaluate horticultural plants before they're introduced into gardens so that some of these invasions can be avoided. It seems to be a difficult thing to evaluate however.

I'm all for reuse and zero-waste, especially in place of things like greeting cards that often, well, get wasted, but this is not necessarily as benign as it seems. One of the seeds included in these greeting cards is Columbine, a native wildflower pollinated by hummingbirds. I'm an aspiring botanist working with native plants here in the Midwest, and the thing about native plants is that they can be extremely localized. The genetics of a plant in one county can be different from the genetics of that same species in the next county over due to climatic, topographical, or geological differences. The danger is in cross-fertilization. If a seed from Texas is planted in Michigan and it grows up and cross pollinates a Michigan bred plant, the offspring may be, for instance, less able to deal with cold temperatures. Native plants are already under a lot of stress, what with habitat loss, pollution, and invasive species. If we're trying to do good things for the environment and revolutionize the greeting card industry in the process, let's make cards out of compost. It's not as pretty, but I'm all for that.