Scale Trees

The Lepidodendrales are an extinct lycophyte group that formed some of the first swamps on Earth. These trees grew to over 100 feet, and over 5 feet in diameter (similar in size to a large oak tree). These trees differed from modern trees, such that they were constructed with a small amount of wood, and large amounts of bark. This made the trees less stable than modern plants, and prone to falling over after a few years of maturity. This created large amounts of plant debris on the swamp floor, which piled up and was compressed over many, many years. This large amount of biomass became the coal that we use as fossil fuels today. The closest, living relatives are the quillworts, Isoetes.

Above: Reconstructions of several lepidodendrids

Ecology and Form

  • Arborescent forms (up to 30m long and 2m wide); small shrubs; sprawling forms living in organic-rich, swampy environments

  • Lepidodendrales had 3 basic habits:

    1. Pole-like stem that branched repeatedly to form a crown only late in an individual’s determinate life span, during which it underwent a progressive developmental shutdown (Andrews and Murdy 1958; Eggert 1961)

    2. Large-diameter trunk but one on which were borne small, deciduous lateral branches in two opposite rows; the reproductive organs terminated these branches

      • These trees also had a determinate crown, and the lateral branches continued to be produced within that crown (Hirmer 1927; Phillips and DiMichele 1992; DiMichele et al. 2013; Chomicki et al. 2017; DiMichele and Bateman 2020); thus, they were functionally polycarpic)

    3. Arboreous Sigillaria, cones were borne directly on the trunk in successive whorls, probably representing paedomorphically reduced lateral branches, and the crown underwent comparatively few apical dichotomies prior to developmental shutdown


  • e.g. Lepidodendron, Sigillaria, Diaphorodendron

  • Pseudo-bipolar growth

    • Root decays early in development

    • Early embryonic shoot splits with one "branch" becoming the "root" or rhizomorph

    • The other shoot become upright stem

  • Exarch primary growth in upright portions, which is different from rhizome system

  • Unifacial (one-faced) cambium in trunk or upright stems

    • Small amount of secondary xylem (wood) produced to the inside (centripetal)

    • No secondary phloem found in the trunk, therefore sugars from photosynthesis could not be transported down to root-like rhizomorph system

    • See rhizomorph description (below) for more details about leaves

  • Large amounts of bark (phellem), which was a major structural support for trunk...

    • ...although D'Antonio & Boyce (2020) indicate that periderm was never greater than 15 cm for observed specimens

  • These trees were probably not as durable as modern trees, with trunk that served the primary purpose of elevating spores during reproduction

    • After spores dispersal, trunks may have fallen over into swamp with strong winds or storms.

    • All of their reproductive organs were produced in the crown, thus rendering them monocarpic or nearly so (Hirmer 1927, fig. 263; DiMichele and Phillips 1985; Chomicki et al. 2017)

Above: XS of stem showing large amounts of bark, but minimal wood

Below: outside bark pattern of Lepidodendron showing scale-like leaf scars

Above: Sigillaria bark (by Hectonichus - Own work, CC BY-SA 3.0, https://commons.wikimedia.org/w/index.php?curid=41691308)

Roots (Rhizomorph)

  • The rooting system consisted principally of two morphologically and developmentally distinct components, the main axes or “rhizomorph” and the appendages generally referred to as “rootlets.” (DiMichele et al. 2022)

    • The rooting system is similar to their closest living relative, Isoetes (Stewart 1947; Hetherington et al. 2016; Hetherington and Dolan 2017)

    • The isoetalean rhizomorph is morphologically distinct from the “rhizophore” of the Selaginellales, a unique root-producing organ in that plant group (e.g., Lu and Jernstedt 1996; Mello et al. 2019);

  • The rhizomorphs (Stigmaria) act like the main root system

    • Endarch primary growth in rhizomorphs, which is different from trunk

    • No true roots in this group; adventitious roots grew from rhizomorph

  • Modified leaves on rhizomorph acts like secondary roots to absorb water and minerals

  • Leaves on the top portions of rhizomorph were probably still green and photosynthetic to provide sugars to growing roots since the trunk lacks secondary phloem

    • Rhizomorph has a rhizotaxis (pattern of root insertion) due to modified leaves growing in a spiraling fashion

    • Modern plants display a phyllotaxis (pattern of leaf insertion) such as the Fibonacci pattern, but modern roots do not have a rhizotaxis

Above: Arboreous lycopsid tree stumps with stigmarian rhizomorphs exposed. A, Line drawing from Williamson (1887, xylograph 7). B, Specimen on public display at the Manchester Museum, United Kingdom. C, Whitefield Tree, displayed on the grounds of the University of Kentucky. D, Specimen illustrated in plate XIX in Potonié (1889). E, Specimen formerly displayed at the US National Museum of Natural History, USNM specimen 34989. A used with permission of the Palaeogeographical Society. B and C courtesy of Steve Greb. (DiMichele et al. 2022)


  • The form genus for the leaves is Lepidophylloides

  • Microphylls or lycophylls leaves like other lycopods

    • Some were very long; up to 14" long

  • Spiral phyllotaxy shown in leaf scars on bark

Reproductive Structures

  • Sporangia were aggregated into cones

  • Plants were heterosporous with both megaspores (female) and microspores (male)

    • Form genus for female cones is Lepidocarpon

    • Form genus for male cones is Lepidostrobus

  • Megaspores (Cystosporites) had endosporic development

    • The female gametophyte is not free-living like other gametophytes of spore-bearing plants

    • The female gametophyte remains mostly inside the megasporangium

    • At maturity, the archegonia of the female gametophyte poke out of the megasporangium for fertilization

    • This is analogous to a seed-like habit, in which seed plants also have a female gametophyte that stays inside of the megasporangium (=nucellus)

  • Microspores (Lycospora) were free-living and produced sperm which was released into a watery environment and would swim to megaspores

  • Some members of this group were possibly monocarpic, reproducing once and then dying, similar to modern century plants (Agave americana)


Above: Lepidodendrid leaves (Lepidophylloides)

Below: Male lepidodendrid cone (Lepidostrobus)



Family Lepidodendraceae † (e.g. Lepidodendron, Lepidophloios, Hizemodendron)

  • Intrafoliar parichnos that extend below the leaf scar

  • Dorsiventrally-flattened megaspore with distal dehiscence

Family Diaphorodendraceae (e.g. Diaphorodendron, Synchysidendron)

  • Medullated protostele

  • Dorsiventrally-flattened megaspore with proximal dehiscence

Family Sigillariaceae † (e.g. Sigillaria)

Family Ulodendraceae † (e.g. Paralycopodites)

Incertae sedis: Sublepidophloios, Bothrodendron, Bergeria, Asolanus


Clevelandodendron ohioensis

  • Chitaley & Pigg 1996

  • Late Devonian (Famennian) of Ohio, USA

  • An unbranched, slender (2 cm wide) plant with a partially preserved plant base bearing thick appendages at the base; apically the plant bears a compact, terminal ovoid bisporangiate strobilus

  • Sporophyll/sporangium complexes attached to axis at 90 angle and extending downward at 60 angle to axis, with prominent distal laminae;

  • Clevelandodendron demonstrates that slender unbranched lycopsids with an isoetalean plant habit similar to the Carboniferous genera Chaloneria and Triassic Pleuromeia were present as early as the Late Devonian.

  • The early occurrence of this unique habit suggests that diversification within the isoetalean clade sensu Rothwell and Erwin (including both Isoetales and Lepidodendrales) was well established prior to the Carboniferous


  • Megaspores, with female gametophytes


  • Anatomically preserved trunks similar to Lepidodendron


  • Female cone (contains megaspores)


  • Upright stem with bark and leaf scars


  • Late Devonian (Famennian) to Lower Carboniferous (Tournaisian and Viséan)

  • This taxon dominated coastal and floodplains of Tournaisian swamps

  • L. kazachstanica (Dou et al. 1983)

  • L. theodori (Sze 1960; Dou et al. 1983; Cai & Wang 1995)


  • Leaves (microphylls)


  • Sporophyll (leaf protecting sporangia)


  • Male cones (contains microspores)


  • Microspore, with male gametophytes

Otzinachsonia beerboweri

  • Cormose (swollen) four-lobed base with masses of attached rootlets

  • The stems exhibited a spiral arrangement of elliptical leaf scars without leaf cushions








Geologic Age

Clevelandodendron ohioensis

Above: Clevelandodendron ohioensis (from Figs 1-4, Chitaley & Pigg 1996)

Below: Otzinachsonia beerboweri. Photo by Walt Cressler.

Protolepidodendropsis pulchra

  • Høeg; Berry & Marshall 2015

  • early Frasnian (Late Devonian) of Svalbard

  • Cormose bases and small ribbon-like roots

  • Their height is unknown but estimated to be around 2 to 4 m. They grew 15–20 cm (6–8 in) apart in wet soils

Protostigmaria eggertiana

  • Cormose rooting organ with multiple lobes

Above: In-situ Protolepidodendropsis fossils (From Fig 4, Berry & Marshall 2015


  • Upright stem with bark and leaf scars

  • This taxon may have been more drought tolerant than other arboreous forms due to unique root system modifications that permitted them to tap into deeper sources of water (Pfefferkorn and Wang 2009; Chen et al. 2022)

  • Sigillarian rootlets possessed a continuously developed so-called connective, a ribbon of tissue that linked the parenchymatous inner cortical region surrounding the vascular strand to the outer cortical zone, thus bridging the central hollow region of the rootlet; connectives were intermittent in the other groups

    • The periderm of the various lycopsid lineages also permits their taxonomic recognition and differentiation given adequate preservation


  • Root-like rhizomorph (modified rhizome-like stem that anchors and absorbs water/minerals)


  • Bateman 1992

  • Mississippian

  • Root-like rhizomorph attached to the bottom of a stem that dichotomously branches, and is similar to Paurodendron in anatomy

  • Relatively large roots with monarch traces are emitted from the base of the stem and rhizomorph

  • Oxroadia resmbles a compact Stigmaria

Additional Resources