Juveniles and Adults in the Plant World

By Lew Feldman, Garden Director

Many plants display two distinct phases in their lifecycle: a vegetative (juvenile) phase, where the plant focuses on increasing biomass but cannot flower, and a reproductive (adult) phase, where the plant gains the ability to produce flowers, fruit, and seeds.

Identifying Juvenile and Adult Foliage
The two phases can often be distinguished on the basis of leaf type. One common example of plants with distinct juvenile and adult leaf types are ivy (Hedera helix) and many species of Acacia. In ivy, which is probably the plant most studied for its phase transitions, leaf shape changes from a 3-5 lobed heart-shaped juvenile leaf to unlobed, entire, ovate or diamond-shaped leaves in the adult form. In most Acacia species, the feathery, divided juvenile leaves are eventually replaced by an undivided leaf-like organ in the adult, known as a phyllode. Phyllodes are actually modified petioles (leaf stalks) that have become flattened and widened to function like leaves, while the original leaf blades are reduced or disappear entirely.

Juvenile English Ivy (Hedera helix) leaves are lobed and heart-shaped.

The adult phase is characterized by a more oval shaped leaf

In addition to changes in leaf shape and flowering capacity, differences between juvenile and adult phases can involve many other features. In ivy the juvenile stems are prostrate (parallel to the ground surface), whereas the adult stems grow upright. In acacias, depending on the species, thorns are more likely observed in the juvenile stage, but become fewer or disappear entirely in the adult form.

Feathery juvenile leaves of acacia

Acacia foliage (phyllodes) and flowers in the adult phase

The Genetic “Master Switch”
Scientists have long known that gibberellic acid (GA), a plant growth regulator, plays a key role in this process; high levels of GA are typically associated with the juvenile phase. More recent research suggests that as GA levels decrease, the transition to the adult phase is triggered by a genetic “molecular switch.” This switch lowers the levels of specific molecular messengers while boosting others. Interestingly, this mechanism appears consistent across the plant kingdom—from simple mosses to complex flowering plants—suggesting that the “clock” governing plant maturity is governed by a nearly universal biological control.

For home gardeners, this transition has a very practical implication: it is significantly harder—and sometimes impossible—to grow successful root cuttings from the adult phase of a plant compared to its juvenile counterpart.