What is this leafy green with a sharp taste, and how do I safely use/cook it? I recently purchased this vegetable at a farmers' market without getting its name. It was marketed as organic/fresh/local in the Northeastern United States in late September.

The leaves are thin and non-waxy, but a little moist (when I try to slide my fingers across the leaves they stick a little).
When I tasted a small portion of a leaf raw, I immediately felt moderate burning in the mouth which I (mistakenly) believed to be oxalic acid at first. In reality, it was a mustardy spicy/sharp taste (which I didn't expect from greens). Because I don't know the name of this plant, I'm not sure if this is the case. In light of that concern, does it require any special preparation to be safe for healthy individuals?
From the photo &amp; description of the leave look &amp; feel, these sound like green wave mustard--a variety of mustard greens with curly leaves.
Mustard greens have a &quot;spicy&quot; or peppery taste, which also seems to align with your experience.
Mustard greens can be safely eaten raw or cooked. It can be a raw salad ingredient, or be sauteed, braised, grilled, etc. Because of the assertive flavor, some people find it best when mixed with other leafy greens to balance out that spiciness you describe.