The question of how many plants exist on Earth seems simple, yet the answer is far from a fixed number. Plants are the foundation of nearly every terrestrial ecosystem, converting sunlight into energy and serving as the primary producers that sustain all other life forms. Determining the sheer scale of the plant kingdom involves navigating complex scientific definitions and overcoming immense logistical hurdles, not just counting individual organisms. This count is constantly being revised as scientists explore remote regions, refine taxonomic definitions, and confront the ongoing challenge of species discovery and loss.
Defining the Boundaries of “Plant”
The first step in answering the question is to establish what, scientifically, counts as a plant. Modern biology defines plants as organisms belonging to the Kingdom Plantae, specifically the group known as Viridiplantae, or “green plants.” This classification includes the land plants, such as trees, flowers, mosses, and ferns, along with a significant portion of what are known as green algae.
This modern definition excludes many organisms that were historically grouped with plants. Fungi, which lack chlorophyll and obtain nutrients by absorption, are now classified in their own kingdom. Similarly, most red and brown algae are excluded from the Plantae kingdom and placed elsewhere, despite their photosynthetic nature. Focusing on this boundary allows scientists to create a more accurate and consistent census of the world’s botanical diversity.
The Current Global Estimate of Plant Species
The most direct answer to the question of “how many plants” is usually given in terms of species diversity. Scientific reviews estimate that there are currently around 391,000 known and described species of vascular plants worldwide. Approximately 369,000 species are flowering plants, representing the most diverse group within the plant kingdom.
While the species count is substantial, it pales in comparison to the sheer scale of the total living plant material on the planet. When scientists measure the collective weight of all life, known as biomass, plants overwhelmingly dominate the Earth’s biosphere. The total biomass of all life is estimated to be approximately 550 gigatons of carbon (Gt C).
Plants account for about 450 Gt C of this total, representing over 80% of all biomass on Earth. This figure highlights that the world is dominated by plants, most of which are land-based, such as the wood and roots of trees. The difference between the species count and the biomass demonstrates the ecological role of the plant kingdom.
Why Counting Plants is an Ongoing Scientific Challenge
Arriving at the figure of approximately 391,000 known species requires a combination of traditional field work and complex statistical modeling. Scientists rely heavily on meticulous records housed in major herbaria, which are vast libraries of preserved plant specimens collected over centuries. Researchers also use statistical methods, such as species accumulation curves, which extrapolate the total number of species based on the rate of new discoveries over time.
One challenge to accurate counting is synonymy, where a single species may have been described and named multiple times by different botanists. Resolving these naming conflicts is a continuous effort that shifts the official count as names are consolidated. Furthermore, many plants, particularly those in remote tropical rainforests, are difficult to access and have not yet been formally described by science.
The count remains fluid because new species are still being discovered at a significant rate; estimates suggest that around 2,000 new plant species are described every year. These newly found plants are often rare, localized to small geographic regions, and found in biodiversity hotspots. This discovery rate is balanced by the threat of extinction, which further complicates the census.
Current estimates suggest that about 21% of all plant species are at risk of extinction, meaning some species may disappear before they are even documented. The total number of plants is not static but a constantly contested figure. This figure is defined by the slow pace of taxonomic work, the inaccessibility of remote biomes, and the dynamic processes of evolution and species loss.