orthostichy

from The Century Dictionary.

• noun In botany, a vertical rank; an arrangement of members at different heights on an axis so that their median planes coincide, as the vertical ranks of leaves on a stem.

from the GNU version of the Collaborative International Dictionary of English.

• noun (Bot.) A longitudinal rank, or row, of leaves along a stem.

from Wiktionary, Creative Commons Attribution/Share-Alike License.

• noun botany A row of leaves along a stem