Please help me identify this plant.
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This is Plectranthus verticillatus. It grows well if the soil is kept dry for a few days between watering and it will gain a bit of colour on the stems. If watered regularly when the light is not too strong, the plant grows bigger and the stems and the venations on leaves remain green, like in your picture.
Yours looks pretty good for a plant that size and if you are wondering when to water, just take a look at the leaves as they will become a little bit softer and will start to roll on the edge when they are thirsty.