Mycorrhizal fungi are the answer, and the arbuscular mycorrhizal fungi cover most of that share. The mycorrhizal fungi land plants rely on grow into the root itself, where they trade soil nutrients for sugar the plant makes up in the leaves. UC Agriculture and Natural Resources puts the partnership in more than 70% of land plants, across a wide range of land ecosystems. That figure is solid. It is also only one of several counts you will run into.
The published percentages disagree because the sources are not counting the same thing. One counts land plants. Another counts plant species, a third counts plant families, and a fourth counts the roots of vascular plants. Those are four different denominators, so you get four different numbers. Blending them into one tidy figure is where most of the bad quotes on this topic start.
Read down that middle column and the argument goes away. Nobody is wrong. Counted by species, the arbuscular fungi partner with almost 90% of plant species. Counted by roots, the same arrangement turns up in 80% of vascular plant roots. Same fungi, two units, two answers. Check which unit a writer used before you repeat any of these numbers, because the swap happens often and it changes what the claim means.
The arbuscular group belongs to the Glomeromycota, a small phylum whose fungi push fine branched structures into living root cells. That branching is the trading floor. Glomeromycota does not fruit into anything you would spot on a walk, so the most common plant partnership on land stays out of sight, under the feet of the people gardening on top of it.
The raw scale behind the percentages is worth holding onto. About 50,000 fungal species are known to form mycorrhizal relationships, and over 95% of plant families have some form of the association. Fossil evidence for the partnership runs back 460 million years, which sets it near the start of plant life on land rather than somewhere along the way. This is not a trick a few odd plants picked up. It is closer to the default setting for a root.
So what does a number like 70% buy you in your own yard? It tells you the plant side is rarely the problem. A vegetable bed, a lawn, and a row of shrubs all sit inside that share, so treat almost everything you plant as a capable host. What changes from bed to bed is the fungal side, and that is a soil question. Ground that gets dug, stripped, or fumigated year after year is the least likely place for native inoculum to have survived.
A high share across all land plants says nothing about your specific bed. It means your plants can host these fungi, not that any given patch of soil still carries them.
That gap matters when somebody tries to sell you a fix. You cannot see colonization without a lab test. A percentage measured across every plant on Earth is no evidence about the corner of dirt in front of you, and no product label can close that distance for you either. Plant into the least disturbed soil you have. The odds that these fungi are already down there sit higher in old, quiet ground than in a bed you rebuild every spring.
Read the full article: Mycorrhizae: What Works and What Is Hype
