Nisha is sorting plants: "small = herb, medium = shrub, big = tree" — going only by height

Why

Nisha's rule works often enough that it feels safe — most herbs really are short and most trees really are tall. But height is a rough hint, not the actual dividing line, and it breaks on real plants. What sorts a plant is its STEM: a herb has a soft, green, non-woody stem; a shrub has several woody stems branching out from near the ground; a tree has one thick woody trunk with branches high up. Test it: a rose bush is short but has several woody stems from the base, so it is a shrub, not a herb; a young mango sapling is short too, but has one woody stem, so it is already a tree; a banana plant is very tall but its stem is soft, so it is a herb. Her friend is right: herb, shrub, and tree are decided by the kind of stem — height only lines up with that most of the time, not always.