sinistrorse

Sinistrorse is an adjective used in biology and related disciplines to indicate a left-handed or counterclockwise orientation of a spiral, coil, or growth pattern. It is the counterpart of dextrorse, which describes a right-handed, clockwise orientation. The precise viewpoint depends on the structure being described: for shells and other coiled forms, sinistrorse denotes a left-handed coil; for climbing plants, sinistrorse refers to stems that wrap around a support counterclockwise when viewed from the base upward, while dextrorse describes clockwise wrapping.

In malacology and conchology, sinistral (or sinistrorse) shells coil to the left; this is relatively rare among terrestrial snails and can have taxonomic or evolutionary significance. Some species may exhibit both sinistral and dextral individuals due to genetic variation, while others maintain a fixed handedness.

In botany, the term is commonly applied to twining climbers and tendrils, where the direction of rotation around a support is used as a descriptive character in keys and descriptions. Sinistrorse and dextrorse growth can influence how plants attach and climb in their environment.

Etymology and related terms: sinistrorse derives from Latin sinistrus "left-handed" with a suffix indicating direction, and is used interchangeably with sinistral in some contexts. The opposite term is dextrorse (dextrorotatory/right-handed). See also chirality and helicity.