If you are unsure as to the content, either ask the herbalist you are purchasing it from, or grown you own and pick it yourself. I say grow your own herbs, then you will know positively the identity of the plant. While very few people die each year from plant mis-identification while wild crafting, picking plants in the wild, it does one no good to be among those dozen or so who make a fatal error. Be safe, buy it dried, or grow it yourself. If dried herbs are not available, fresh plants may be substituted.
Alchemists have personal preferences as to when an where to use fresh versus dried plants.
Experience will help you sort this out later on. For now, either plant will suffice for this experiment. The 190 proof is sufficient, and the most commonly used in plant work for beginners. If neither of these is available, vodka can be substituted, or alcohol can be distilled from red wine, or strong brandy. Check if you think this may be a problem.