Sigillaria was one of the most striking and unusual plants of the Paleozoic era, flourishing from the late Carboniferous to the end of the Permian period around 254 million years ago.

Though it resembled a towering tree, it was actually a giant lycophyte - an ancient relative of modern club mosses. Reaching heights of up to 30 meters, Sigillaria had a tall, unbranched (or occasionally forked) trunk covered in photosynthetic tissue, giving it a green, vibrant appearance from canopy to base. Its long, grass-like leaves sprouted in a spiral from near the top of the trunk, forming a brush-like crown.

As the lower leaves fell away, they left behind diamond-shaped scars arranged in vertical rows, creating a distinct pattern that inspired the plant’s name - Sigillaria, from the Latin sigillum, meaning “seal.”

Unlike modern trees, Sigillaria lacked true wood. Instead, its support came from a dense outer layer of leaf bases beneath the surface, while its center was filled with soft pith.

It reproduced by releasing spores from cone-like structures hanging from its stem, and these spores came in two sizes—microspores and megaspores—indicating a complex reproductive strategy known as heterospory.

It thrived in coal swamp forests alongside its close relative Lepidodendron, especially in better-drained soils on river floodplains, which helped it endure drier conditions that challenged other swamp plants.

Its fossilized trunks and roots, marked with their characteristic leaf scar "seals," remain some of the most recognizable plant fossils from the Carboniferous period.

As a dominant feature of prehistoric landscapes, Sigillaria played a vital role in shaping ancient ecosystems and contributing to the vast coal beds that power our world today.