Definition of orthostichy in US English:

orthostichy

nounPlural orthostichies

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

    Contrasted with parastichy
    • ‘Spiral phyllotaxis patterns have only parastichies, whereas whorled patterns have both orthostichies and parastichies.’
    • ‘Phyllotactic rows are easiest to identify in columnar cacti because vertically aligned leaf primordia merge together forming ribs (orthostichies).’
    • ‘Longitudinal section of shoot apex and an orthostichy of leaf primordia that are forming a rib.’
    • ‘On the dorsal surface of the branch there are also two orthostichies of leaves of the usual form.’
    • ‘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.’

Origin

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

Pronunciation

orthostichy

/ôrˈTHästikē/