Citrus Tree Leaves Identification Chart: 10 Types by Leaf

Citrus leaves identification starts with four checks, all taken from Citrus ID, the citrus identification tool on idtools.org, the identification site of the US Department of Agriculture's plant protection program.

• Leaflet count. Cultivated citrus leaves are unifoliolate: a single leaflet on a petiole. Three leaflets means trifoliate orange or one of its hybrids.
• Petiole wings. The leaf stalk may be bare or carry a leafy wing from narrow to wide. Wings vary even on one tree, so Citrus ID says to look at a number of leaves and go by the usual form.
• Scent. Crush a young leaf. Citrus ID calls this one of the most helpful characters: sweet in sweet oranges, grapefruits and pummelos; freshly spicy in lemons; spicy or peppery in sour oranges; bread-dough in calamondins.
• Shape and folding. Leaves in full sun fold along the midrib and get wavy edges; shade leaves are flatter. Compare leaves from the same side of the tree.

From the Citrus ID fact sheets, which quote Swingle and Reece (1967) and other standard references:

• Lemon - light green, lanceolate leaves with short, wing-margined petioles; young leaves and flower buds reddish, new shoots purple-tinted; margins serrate; crushed leaf freshly lemon-like.
• Meyer lemon - short petiole, wings absent or narrow; scent sweetly orange-like or lemon-like.
• Key (West Indian) lime - small leaves, 5 to 7.5 cm, pale green, narrowly winged petioles, twigs with short, very sharp spines. Citrus ID notes it has much smaller, paler leaves and far more thorns than the Tahiti lime.
• Tahiti or Bearss lime - short petiole without wings; freshly lemon-like scent.
• Sweet orange - petiole wings absent or narrow to wide; margins entire to bluntly toothed; sweetly orange-like scent.
• Sour orange - petioles 2 to 3 cm long and rather broadly winged, often 1.2 to 1.8 cm wide at the top. Ruggieri (1935), quoted by Citrus ID, measured sour orange petioles at 25.89 mm on average against 15.91 mm for sweet orange, 63% longer. The leaf is darker and more taper-pointed than sweet orange.
• Grapefruit - leaves larger than sweet orange and smaller than pummelo, with rather broadly winged petioles that are not as broad as pummelo's.
• Pummelo - large to very large leaves whose rounded base can overlap the petiole wing; wings broad and more or less heart-shaped; young twigs and midribs often downy.
• Mandarin - wings absent, or narrow to medium; mandarin-like scent.
• Kumquat - small, rather thick, blunt leaves; the underside is pale green with very numerous small dark-green oil dots; petioles narrowly winged or only margined.
• Citron - short, wingless petiole not clearly jointed to the blade; serrate margins; stout, short spines; lemon-like scent.
• Trifoliate orange - three leaflets, deciduous, single stout spines; leaflets not scented.

Four quick checks, in order:

• New growth color. Lemon shoots and young leaves are purple or reddish; lime new growth is not described that way.
• Leaf size and color. Key lime leaves are small (5 to 7.5 cm) and pale; lemon leaves are longer and lanceolate.
• Thorns. Key lime is very thorny with short, sharp spines.
• Scent. Both can smell lemon-like, so scent helps less here than between orange and lemon.

If the tree has fruit, that settles it; if not, Citrus ID's point applies: check many leaves, not one.

Most citrus trees are grafted onto a rootstock, often trifoliate orange or one of its hybrids. Greg Alder's guide to reading citrus leaves points out that rootstock suckers show three-leaved clusters and a lot of thorns. If shoots below the graft union carry three leaflets, they are rootstock growth rather than the variety you bought; the Citrus ID sheet confirms trifoliate orange leaves have three leaflets and no scent.

Greg Alder's field notes and a University of Florida IFAS publication cover the common signs:

• Squiggly tracks, curled shiny leaves - citrus leafminer.
• Yellow blotches with white fluff underneath - woolly whitefly.
• Orange or brown bumps - scale insects; ants tending them are a clue.
• Black film - sooty mold growing on honeydew from sap-sucking insects.
• Cupped, rolled leaves - thirst; they unroll within hours of watering.
• Dark, water-soaked leaves in winter - cold damage.
• Yellow blotches along the midrib of mature leaves near fruit, leaving an inverted green V at the base - magnesium deficiency (UF/IFAS). UF/IFAS adds that magnesium deficiency appears only on mature leaves, while deficiencies of iron, zinc, manganese and copper show on new growth.

New growth that is slightly yellow before it matures is normal, Greg Alder notes.

Epsom salt is magnesium sulfate (Wikipedia), so it only addresses one problem: magnesium deficiency. UF/IFAS says soil application of magnesium sulfate or oxide can correct a deficiency when soil pH is raised, that foliar sprays of magnesium nitrate can work on spring and summer flush leaves that are two-thirds to fully expanded, and that one foliar spray is not always enough. It lists the optimum leaf range as 0.30 to 0.49% magnesium in 4- to 6-month-old spring flush leaves from non-fruiting twigs, and names acidic sandy soils and fertilizers high in potassium as common causes.

So confirm the inverted-V pattern on older leaves, or get a leaf test through your local extension office, before adding magnesium. Yellowing on new growth points to a different nutrient.

The same method, leaf arrangement first and details second, works on any tree. Our oak leaf identification and maple leaf identification guides walk through two common groups. For a quick answer, WoodLens can identify a tree from a photo of a leaf, bark or wood.