The subtropical evergreen family of citrus trees is very popular throughout the world for landscaping, culinary and medicinal purposes. Although the trees may be easily recognizable by the fruit on the branches, it is important to understand how to identify citrus trees by their foliage, shape or flowers in case the tree has no fruit on it at the moment. The most common citrus trees on landscapes include mandarins, oranges, grapefruits, lemons and limes. All citrus trees cannot survive in temperatures that drop below 20 degrees Fahrenheit.
Examine the size of the citrus tree, as some grow small and squat and others are tall and skinny. Grapefruit and orange trees can grow to more than 30 feet tall, and they appear rounder in shape. Limes and lemons usually don't exceed 10 to 15 feet and have a shrubby appearance. Mandarin trees usually grow around 15 feet tall but can reach 25 feet at full maturity. Consider branch shape as well. Limes have slender, spiky branches, and lemons have twiggy branches with thorny offshoots.
Observe the fruit on the citrus tree if there is any apparent. Consider the size and shape of the fruit, particularly the color. Lemons are bright yellow, are 2 to 4 inches long and have an oval shape. Grapefruits range from a paler shade of yellow to pinkish yellow to bright yellow, have a round shape, and are large and heavy, averaging around 4 inches in diameter (larger than any of the other citrus). Limes are much smaller and bright green, 1 to 2 inches in diameter. Oranges are bright orange and spherical, 2 to 4 inches in diameter. Oranges are usually bumpy with a thick rind.
Look at the shape and size of the leaves. Lemon trees have elliptical leaves with fine-tooth edges, dark green on top and light green on the bottom, and the leaves grow close together. Lime trees have similar leaves but are very glossy and grow 2 to 4 inches long, and the leaves grow separately. Orange tree leaves are very dark green and glossy, with a rounded base, and are 3 to 5 inches long. Tangerine leaves are the same but a little smaller and grow in clumps. Grapefruit leaves are very glossy and range from 3 to 5 inches long. They have a round base and pointed tip.
Check for flowers on the citrus tree. All of the trees flower before fruiting with small, white flowers. Lemon, lime and orange trees have flowers that have a strong, sweet fragrance, while the grapefruit tree flowers do not have any aroma. Lemon and lime flowers also have a slightly pink to purple-tinged underside.