Monochasial

Monochasial is a term used in botany to describe a pattern of branching in which a single main axis bears lateral branches on only one side, while the main axis continues to grow. This results in a zigzag or unilateral growth habit. The side on which the lateral branch arises can be used to describe the form as monochasial-left or monochasial-right.

Monochasial branching contrasts with dichotomous branching, where the axis splits into two roughly equal branches at a node, and with polychasial branching, where multiple lateral branches arise from a single node. In addition to vegetative branching, the concept is applied to inflorescences, where monochasial cymes produce flowers successively on one side of the axis.

Occurrence and use: Monochasial patterns are observed in a variety of plant groups, including some ferns and lycophytes, and are noted for describing growth forms and inflorescence architecture. The term is descriptive and used to characterize morphology rather than to designate a taxonomic group.

Related concepts: Dichasia or dichasial branching (two-sided), monochasia as a related term for one-sided growth, and other branching modalities such as sympodial and monopodial growth describe different ways the main axis continues after branching.