sympodium

from The American Heritage® Dictionary of the English Language, 5th Edition.

• noun An apparent axis that develops when growth occurs by means of lateral branches rather than continuing along the principal stem, often having a zigzag or irregular form.

from The Century Dictionary.

• noun In botany, an axis or stem which imitates a simple stem, but is made up of the bases of a number of axes which arise successively as branches one from another. The grape-vine furnishes a perfect example. Compare monopodium and dichotomy. Also called pseudo-axis.

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

• noun (Bot.) An axis or stem produced by dichotomous branching in which one of the branches is regularly developed at the expense of the other, as in the grapevine.

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

• noun A pattern of branching, similar to dichotomous branching.