Final answer:
Horsetail capsules derive from the genus Equisetum, featuring jointed, hollow stems rich in silica, which serve as an ancient scouring tool and present benefits in herbal medicine for kidney and bladder health. These plants were prominent in the formation of coal and oil and continue to be widespread in terrestrial habitats.
Step-by-step explanation:
Horsetails, known scientifically as the genus Equisetum, have distinctive jointed stems with whorls of small leaves that resemble the appearance of a horse's tail. These stems are hollow and ribbed, reflecting an ancient lineage of plants that were once scrubbing tools, and today, find their role in various applications including herbal remedies. Horsetails are remarkable for their ability to perform photosynthesis primarily through their stems instead of leaves and for possessing silica within their epidermal cells, contributing to their structural stiffness.
In modern times, horsetail capsules are mainly utilized for their purported health benefits. Herbalists employ these capsules to help treat kidney and bladder issues, such as infections and stones, as well as to remedy brittle nails. Moreover, the abrasive nature due to the high silica content made these plants useful as metal polishers and cleansing abrasives historically.
The expansiveness of horsetails in the Paleozoic era bears witness to their dominance in terrestrial habitats, contributing significantly to today's coal and oil reserves. The spore-producing structures of horsetails, known as strobili, disperse spores with the help of elaters, enabling the plant to reproduce and colonize new areas across various habitats worldwide.