Oxalidaceae

Trifoliate (or multi-leafleted) leaves that visibly fold down and close at night or when touched; five-petalled flowers with sour, oxalic-acid-rich tissue ripen into a capsule that, in star fruit, forms a distinctive five-ridged, star-shaped cross-section.

Sharply sour oxalic acid runs throughout the leaves and fruit — pleasant in small amounts in wood sorrel and star fruit, but toxic to kidneys in large quantities.

To check whether a plant belongs to Oxalidaceae, compare the leaf arrangement, leaf type, flower symmetry, fruit type, and one distinctive marker together. A single feature can mislead; the family pattern is the combination.