Averrhoa carambola aka Starfruit

Averrhoa carambola is the tree that bears star fruit. It belongs to the wood sorrel family, Oxalidaceae. Kew places its native range from central and eastern Java to Maluku. Other sources give a broader Southeast Asian origin. Growers now raise it across tropical and warm subtropical regions. It grows in humid forests and woodland on sandy loam.

This evergreen tree has a short trunk and many branches. Its crown spreads into a broad, rounded shape. Garden accounts give heights of 20–33 feet [6–10 metres]. Some sources describe smaller trees, at 10–16 feet [3–5 metres]. Others report heights reaching 39 feet [12 metres]. Its spread can reach 30 feet [9.14 metres]. Sources differ on whether growth is slow or fast. Cool weather can cause some or all leaves to fall. The green, pinnate leaves carry several smaller leaflets. These fold at night or when touched.

Small, scented flowers range from pink to lavender or rose. They grow in clusters on twigs and sometimes larger branches. Bees and flies visit the flowers. The fleshy berries have thin, waxy, yellow skin when ripe. Raised ribs give cut slices their star shape. The flesh is crisp, juicy, and low in fibre. Fruit flavour ranges from sour to sweet. People eat it fresh or make juice, jam, and pickles. Flowers, leaves, and seeds also have recorded food uses.

Grow this tree in full sun with shelter from wind. It needs rich, acidic loam that drains well but stays moist. Drought can cause leaf loss and reduce flowering and fruit size. It suits USDA zones 10–12 and does not tolerate frost well. Growth slows or stops as temperatures fall. In cold regions, containers need an indoor home for winter. Such plants may fail to bear fruit. In warm gardens, it provides fruit, shade, and year-round green foliage. Growers also train it as bonsai.

Serious pest and disease trouble is not usual. Wet soil can lead to root rot. Leaf spots, anthracnose, and sooty mould can also occur. Fruit flies, beetles, caterpillars, scale, and stinkbugs may attack it. The fruit contains oxalates and the nerve toxin caramboxin. People with kidney disease should avoid it unless their doctor approves. Sour fruit can poison pets and harm their kidneys. Sweet fruit poses less risk to pets with healthy kidneys. Recorded folk remedies do not establish that medicinal use is safe.