30 different plants a week sounds ambitious — spices and small servings count, and it's more achievable than it sounds.
Popularised partly by the American Gut Project, this research found that people who ate 30 or more distinct plant types (vegetables, fruit, whole grains, legumes, nuts, seeds, herbs and spices all count) in a week had meaningfully more diverse gut microbiomes than those eating fewer than 10 — diversity that's independently associated with better markers of gut and immune health.
Different plants feed different strains of gut bacteria. Eating a large volume of the same few vegetables repeatedly supports a narrower set of bacterial strains than eating smaller amounts of many different plants — variety, not volume, appears to be the more important lever here.
Herbs, spices and even small amounts of different vegetables in a single dish all count toward the 30 — this is a much more achievable target than it initially sounds, especially if you count spices and variety within meals rather than only whole separate dishes.
This is part of why THE FAD's Food signal specifically rewards plant diversity, not just "ate vegetables today" as a single checkbox.