The question of whether all herbs are plants is a common source of confusion because the word “herb” holds two distinct meanings. The straightforward answer is yes, every herb is a plant, but the botanical definition and the common usage definition are not the same. Understanding the term requires separating how botanists classify the plant structure from how people utilize the plant’s properties. This dual nature means some plants widely known as herbs do not technically fit the scientific category.
Defining the Term Herb
The ambiguity of the term “herb” arises from its usage across both scientific classification and human utility. In the most general sense, an herb is any plant whose leaves, seeds, or flowers are used for flavoring, medicine, or fragrance. This functional definition is what most people encounter in cooking or traditional health practices. However, the scientific community uses a much more specific, structural definition. Botanists use the term to refer to a specific type of plant known as an herbaceous plant, focusing on the physical characteristics of the plant’s stem and its life cycle.
Structural Classification: Herbaceous Versus Woody Plants
From a botanical perspective, an herb is precisely defined as an herbaceous plant. This is fundamentally a plant that does not develop a persistent, woody stem above ground. Woody plants, such as trees and shrubs, develop rigid stems reinforced by lignin, a complex organic polymer that provides strength and durability. In contrast, herbaceous plants have soft, flexible, green stems composed primarily of cellulose, which lacks structural rigidity.
The aerial parts of these plants typically die back to the ground at the end of the growing season or during winter. Herbaceous plants can follow different life cycles, including annuals, biennials, and many perennials whose roots survive underground to regrow. This die-back mechanism separates them from woody plants, whose stems persist above ground year after year. For example, while rosemary is commonly called an herb, its woody, persistent stem means it is botanically classified as a shrub, not an herbaceous plant.
Functional Classification: Culinary and Medicinal Uses
The common understanding of “herb” is almost exclusively functional, focusing on the plant’s aromatic properties. In the culinary world, an herb typically refers to the fresh or dried leafy green parts of a plant used in small quantities for seasoning food, such such as basil, parsley, or mint. This usage separates herbs from spices, which are derived from other parts of the plant, such as dried bark, seeds, roots, or fruit. When used for medicinal or aromatic purposes, the definition expands to include a wider range of plant parts and types, and it is not limited to non-woody species. For instance, the leaves of a bay tree or the berries of a juniper shrub are functionally considered herbs despite their woody classification.