Definition of orthostichy in US English:

orthostichy

noun

Botany
  • (in phyllotaxis) a vertical row of leaves arranged one directly above another.

    Contrasted with parastichy
    • ‘On the dorsal surface of the branch there are also two orthostichies of leaves of the usual form.’
    • ‘Phyllotactic rows are easiest to identify in columnar cacti because vertically aligned leaf primordia merge together forming ribs (orthostichies).’
    • ‘Typically, they traverse the same number of internodes between the position at which they diverge from the minor axial bundles until they enter the branch base as the number of leaf orthostichies on the shoot.’
    • ‘Longitudinal section of shoot apex and an orthostichy of leaf primordia that are forming a rib.’
    • ‘Spiral phyllotaxis patterns have only parastichies, whereas whorled patterns have both orthostichies and parastichies.’

Origin

Late 19th century: from ortho- ‘upright, straight’ + Greek stikhos ‘row, rank’.

Pronunciation

orthostichy

/ôrˈTHästikē/