This is a young meyer lemon tree grown from seed. Maybe about 1-2 years old. Leaves get darker in warmer seasons with more sun. Does well as an indoor plant near a window.
Citrus × meyeri, the Meyer lemon (Chinese 香柠檬 xiangningmeng), is a hybrid citrus fruit native to China. It is a cross between a citron and a mandarin/pomelo hybrid.
Mature trees are around 6 to 10 ft (2 to 3 m) tall with dark green shiny leaves. Flowers are white with a purple base and fragrant. The fruit is rounder than a true lemon, deep yellow with a slight orange tint when ripe, and has a sweeter, less acidic flavor. The lemons contain a highly acidic pH of between 2 and 3. This acidity level allows for these lemons to be used as antibacterial and antiseptic cleaners.
It was introduced to the United States in 1908 as S.P.I. #23028 by the agricultural explorer Frank Nicholas Meyer, an employee of the United States Department of Agriculture who collected a sample of the plant on a trip to China. Though it is given his name, this variety was established as 香柠檬 likely thousands of years before he introduced it to America.