A botanist studying a plant with geographically separated and morphologically distinct populations ...

Two classic experimental approaches would be useful here. The first is reciprocal transplant, which involves switching the environments of the plants, for example, by creating test plots in each area and planting seeds or seedlings collected from the other site. The second would be to create a common garden, in which seeds or seedlings of plants from each population are reared under identical conditions, for example, side by side in a greenhouse. Comparison of key morphological traits across the populations will provide a way to estimate heritability of the traits.