How did Equisetopsida plants become important in Carboniferous coal-forming forests?

During the Carboniferous Period, members of the class Equisetopsida—specifically the treelike genus Calamites—played a significant role in the formation of coal deposits. These plants became important contributors to coal-forming forests due to several key factors:

• Tree-like Stature: Unlike modern horsetails, which are typically small and herbaceous, Calamites grew as large trees, reaching heights of up to 30 metres (100 feet) and diameters of 1 metre (3 feet).12
• Swamp Habitats: These plants thrived in the wet, equatorial environments that characterized the coal swamps of the Carboniferous.132
• Vigorous Growth: Calamites possessed the ability to sprout vigorously from underground rhizomes, allowing them to recover and persist even when their upper portions were damaged.4
• Abundance: As part of the diverse flora of the era, their massive remains accumulated in these swampy basins, where they were eventually transformed over millions of years into the coal used as a fuel source today.41

While other plants like lycopsids also contributed to these forests, the extinct giant sphenophytes were a defining component of the vegetation that fueled the creation of major coal beds.12