Lepidodendrales (Lepidodendron or Sigillaria)

            Lepidodendrales (Lepidodendron or Sigillaria) refers to a group of extinct arborescent lycopsid plants that dominated the wetland forests of the Carboniferous period, approximately 359 to 299 million years ago. These tree-like vascular plants formed extensive tropical coal-forming swamps across what are now Europe and North America. While precise identification may be uncertain in many fossil specimens, they are typically attributable to one of the two principal genera within this group: Lepidodendron or Sigillaria.

Lepidodendrales are members of the division Lycopodiophyta, a lineage of primitive vascular plants distinguished by their simple leaves (microphylls), dichotomous branching, and reproduction by spores. Unlike modern lycopsids—such as clubmosses (Lycopodium)—the Carboniferous representatives attained impressive sizes and developed highly specialised growth and reproductive strategies to thrive in humid, waterlogged environments.

Individuals within this group often exceeded 30 metres in height, with trunks sometimes over a metre in diameter. These plants lacked true wood, instead relying on a thick, photosynthetic cortex and a relatively thin layer of vascular tissue to provide structural support. The interior of the stem was composed largely of soft parenchymatous pith, and the outer surfaces were marked by a quilted pattern of leaf scars arranged in regular spirals or vertical rows, depending on genus. In Lepidodendron, these scars formed rhomboidal patterns, while in Sigillaria, they tended to be more vertically elongated and organised into distinctive rows, often with prominent grooves (parichnos) associated with gas exchange.

Despite their massive size, Lepidodendrales had relatively short lifespans. These trees followed a rapid growth cycle, reaching maturity within decades before producing spore-bearing cones (strobili) and dying shortly thereafter. Reproduction was heterosporous, with megaspores and microspores borne in separate structures, usually at the tips of branches. The spores were dispersed into the surrounding swamp atmosphere, where they germinated into gametophytes independent of the parent plant.

The rooting structures of Lepidodendrales are referred to as Stigmaria, a form genus used for the distinctive, radially spreading subterranean systems associated with these trees. Stigmaria rootstocks bore spirally arranged rootlets and often formed dense networks in ancient soils (palaeosols), anchoring the trees in soft, water-saturated substrates. These root systems were often as robust as the aerial trunks, and are among the most commonly preserved plant fossils in Carboniferous coal measures.

Lepidodendrales flourished in low-lying, equatorial wetlands, where high humidity, stable temperatures, and waterlogged soils provided ideal conditions for their growth. The elevated atmospheric oxygen levels of the Carboniferous—likely exceeding 30%—further supported the gigantism seen in both plant and animal life during this period. These lycopsid forests played a crucial role in carbon sequestration and the formation of extensive coal beds that remain economically important today.

The decline of Lepidodendrales coincided with climatic shifts towards drier and more seasonal conditions during the late Carboniferous and early Permian. As the great tropical wetlands fragmented and contracted, seed-bearing plants such as early conifers and pteridosperms came to dominate upland and more arid habitats, eventually replacing the lycopsid forests entirely.

Fossils of Lepidodendrales are among the most abundant and recognisable components of Carboniferous strata. Their bark impressions, root systems, and spore cones are commonly found in situ, preserved in fine-grained mudstones, siltstones, and coal seams.

Taken in: UK / Scotland / Crail (show map)

Taken on: June 18, 2025

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Camera: Nikon D5600, f/8.0, 1/400 sec, 18mm (=27mm), ISO 100 (more info) (hide info)

Camera:	Nikon D5600
Aperture:	f/8.0
Exposure Time:	0.003 sec (1/400)
Focal Length:	18mm (35mm equivalent: 27mm)
ISO:	100
Exposure Bias:	-1 EV
Flash:	Off, Did not fire
Exposure Program:	Aperture-priority AE
Exposure Mode:	Auto
Metering Mode:	Multi-segment
White Balance:	Manual
Light Source:	Cloudy
Color Space:	sRGB
Software:	Ver.1.10
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