Sigillaria sp.
Sigillaria is an extinct genus of arborescent lycopsid plants that formed a major component of Carboniferous swamp ecosystems, particularly during the Late Carboniferous period (approximately 323 to 299 million years ago). These towering, spore-producing trees were close relatives of Lepidodendron and belonged to the order Lepidodendrales, within the division Lycopodiophyta—a group of ancient vascular plants characterised by microphyllous leaves and dichotomous branching.
Unlike Lepidodendron, which displays a diamond-shaped leaf scar pattern, Sigillaria is readily distinguished by its vertically aligned rows of elongated leaf scars, often bordered by distinctive grooves called parichnos. These surface features give the bark a banded or ‘sealed’ appearance, from which the genus derives its name (Latin sigillum, meaning ‘seal’). The scars represent points of attachment for long, narrow microphylls, which covered much of the trunk surface during the tree’s life.
Sigillaria was capable of reaching heights in excess of 20 to 30 metres, with trunks up to a metre in diameter. Like other Lepidodendrales, it did not produce true wood. Instead, structural support was provided by a thick, photosynthetic cortex surrounding a central parenchymatous core. The plant’s ability to grow rapidly and achieve great height in soft, waterlogged soils was critical to its ecological dominance in Carboniferous wetland forests.
The rooting system of Sigillaria, classified under the form genus Stigmaria, featured radiating rootlets arranged in a spiral around horizontal rhizomes. These extensive roots anchored the tree in swamp substrates and are commonly preserved as fossils, often associated with upright trunk remains in coal measures.
Sigillaria reproduced by means of spores produced in cone-like strobili located at the ends of its branches. Like other lycopsids, it was heterosporous, bearing megaspores and microspores in separate organs. The life cycle included an alternation of generations, with the large sporophyte phase (the tree) dominating and a much-reduced gametophyte stage developing independently.
The decline of Sigillaria during the Permian is linked to the drying of Carboniferous wetlands and the expansion of seed-bearing plants. However, during its peak, Sigillaria was among the tallest and most ecologically important plants on Earth, forming vast, mono-dominant stands in tropical lowland swamps.
