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Scale Trees
Scale Trees
The lepidodendrids are an extinct lycophyte group that dominated 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 in 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 quantities of plant debris on the swamp floor, which accumulated and was compressed over many years. This large amount of biomass became the coal that we use as fossil fuels today. The closest living relatives are the quillworts, specifically the genus Isoëtes.
Above: Reconstructions of several lepidodendrids. From left to right, juvenile lepidodendrid, Lepidodendron †, Lepidophloios †, and Sigillaria †
Ecology & Form
Ecology & 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:
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)
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)
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
Stems
Stems
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 becomes an upright stem
Exarch primary growth in upright portions, which is different from the rhizome system
Unifacial (one-faced) cambium in trunk or upright stems
A small amount of secondary xylem (wood) is produced toward the inside (centripetal)
No secondary phloem found in the trunk, therefore, sugars from photosynthesis could not be transported down to the 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 the 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 trunks that served the primary purpose of elevating spores during reproduction
After spores are dispersed, trunks may fall over into the 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; DiMichele and Phillips, 1985; Chomicki et al., 2017)
Above: Cross-section 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)
Roots & Rhizomorphs
Roots & Rhizomorphs
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 & 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 & 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: Arborescent 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)
Leaves
Leaves
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
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 the megasporangium (=nucellus)
Microspores (Lycospora †) were free-living and produced sperm, which were 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 †)
Diversity
Diversity
Bothrodendraceae †
e.g., Bothrodendron, Arthrocladion, Barsostrobus
Diaphorodendraceae †
e.g., Diaphorodendron, Synchysidendron
Medullated protostele
Dorsiventrally-flattened megaspore with proximal dehiscence
Lepidodendraceae †
e.g., Lepidodendron, Lepidophloios, Hizemodendron
Intrafoliar parichnos that extend below the leaf scar
Dorsiventrally-flattened megaspore with distal dehiscence
Sigillariaceae †
e.g., Sigillaria
Ulodendraceae †
e.g., Paralycopodites
Incertae sedis: Sublepidophloios †, Bergeria †, Asolanus †
Taxa
Taxa
Arthrocladion rhodii †
Arthrocladion rhodii †
Sauveur, 1848
Carboniferous of Belgium
Barsostrobus famennensis †
Barsostrobus famennensis †
Fairon-Demaret, 1977
Famennian of Belgium
Bothrodendron †
Bothrodendron †
Lindley & Hutton, 1833
B. brevifolium
Nathorst, 1902
Late Devonian of Sweden
B. pacificum
Steinmann, 1928
Carboniferous of Peru
Classification
Classification
└Lepidodendrales †
Above: Clevelandodendron ohioensis (from Figs 1-4, Chitaley & Pigg 1996)
Cystosporites †
Cystosporites †
Schopf, 1938
Megaspores, with female gametophytes
C. barbatus
C. bennholdii
C. breretonensis
C. fimbriatus
C. giganteus
C. indicus
C. lageniculoides
C. strictus
C. varius
C. verrucosus
C. zerndtii
Diaphorodendron decurtatum †
Diaphorodendron decurtatum †
Middle Pennsylvanian of Canada
Anatomically preserved trunks similar to Lepidodendron
Hizemodendron serratum †
Bateman & DiMichele, 1991
Moscovian of Illinois
Originally called Lepidodendron serratum
Jurinodendron †
Jurinodendron †
Doweld, 2001
J. aegypticum
J. australe
J. brasiliense
J. brevifolium
J. cambricum
J. dasyphyllum
J. hercynium
J. macconochiei
J. majus
J. pacificum
J. primorskiense
J. sigillarioides
J. sinaicum
J. ungeri
J. ursinum
Lepidocarpon †
Lepidocarpon †
Scott, 1900
Female cone containing megaspores
L. bohdanowiczii
L. braidwoodense
L. cultriforme
L. glabrum
L. ioense
L. lomaxii
L. magnificum
L. takhtajanii
L. wildianum
Lepidodendron †
Lepidodendron †
Sternberg, 1820
Upright stem with bark and leaf scars
L. acerosum
L. aculeatum
L. acuminatum
L. adygense
L. affine
L. albanense
L. alternans
L. alveolare
L. anglicum
L. anomalum
L. appendiculatum
L. batovii
L. bloedii
L. boureaui
L. caelatum
L. confluens
L. crenatum
L. dichotomum
L. elongatum
L. fusiforme
L. griffithii
L. hastatum
L. hexagonum
L. imbricatum
L. kemeroviense
L. laricifolium
L. laricinum
L. liasokeuperinum
L. lissonii
L. lycopodioides
L. megastomum
L. minimum
L. minutum
L. oblongum
L. obovatum
L. ornatissimum
L. ostrogianum
L. papastaramense
L. peruvianum
L. phlegmaria
L. prokopievskiense
L. punctatum
L. rhodeanum
L. rimosum
L. selaginoides
L. sibiricum
L. spetsbergense
L. tamense
L. taxifolium
L. tesselatum
L. tetragonum
L. tomiense
L. tonderae
L. trigonum
L. tyrganii
L. undulatum
L. usovii
L. volkmannianum
Lepidodendropsis †
Lepidodendropsis †
Lutz, 1933
Late Devonian (Famennian) to Lower Carboniferous (Tournaisian and Viséan)
This taxon dominated the coastal and floodplains of the Tournaisian swamps
L. africana
L. baranovkensis
L. breviinternodia
L. concinna
L. cyclostigmatoides
L. devoogdii
L. fenestrata
L. fusiformis
L. guanzuangensis
L. hirmeri
Lutz, 1933 [type]
Tournaisian of Germany
L. karakubensis
L. kazachstanica
Senkevitsch, 1961; Dou et al. 1983
Givetian of Kazakhstan
L. lissonii
L. lutzii
L. niuewanensis
L. orientalis
L. ovata
L. ovoida
L. parvipulvinata
L. peruviana
L. pranabii
L. prisca
L. schuermannii
L. shaoyangensis
L. sigillarioides
L. sinaica
L. sinensis
L. songziensis
L. steinmannii
L. taoshanensis
L. theodorii
Sze 1960; Dou et al. 1983; Cai & Wang 1995
L. tiaomaensis
L. vandergrachtii
L. varia
L. yangtziensis
L. yiduensis
Lepidophloios †
Lepidophloios †
Sternberg, 1825
L. acadianum
L. acerosum
L. antiquum
L. crassicaule
L. crassicaule
L. geminum
L. gracile
L. ichthyoderma
L. ichtyolepis
L. irregulare
L. laricinum
L. lepidophyllifolium
L. macrolepidotum
L. orientale
L. parvum
L. platystigma
L. prominulum
L. tetragonum
L. vsevolodii
L. yajidoensis
Lepidophylloides †
Lepidophylloides †
Snigirevskaya, 1958
Leaves (microphylls)
L. aciculum
L. alatum
L. angulatum
L. delicatum
L. hippocrepicus
L. latifolium
L. morrisianum
L. sclereticum
L. taiyuanensis
Lepidostrobophyllum †
Lepidostrobophyllum †
Hirmer, 1927
Sporophyll (leaf protecting sporangia)
L. alatum
L. brevifolium
L. caudatum
L. hastatum
L. lanceolatum
L. majus
L. ovatifolium
L. rotundatum
L. tongshanense
L. xiphidium
Lepidostrobus †
Lepidostrobus †
Brongniart, 1828
Male cones (contains microspores)
L. acutisquamus
L. ambiguus
L. aristatus
L. arrectus
L. attenuatus
L. bailyanus
L. bartlettii
L. bohdanowiczii
L. braidwoodensis
L. brongniartii
L. brownii
L. brownii
L. collombianus
L. comosus
L. dabadianus
L. dentatus
L. dubius
L. emarginatus
L. fastigiatus
L. faudelii
L. fischeri
L. gallowayi
L. geinitzii
L. gemmiformis
L. germarii
L. giganteus
L. giganteus
L. globosus
L. goldenbergii
L. grabaui
L. gracilis
L. gracilis
L. hibbertianus
L. hookeri
L. imbricatus
L. insignis
L. kashmirensis
L. latus
L. laurentii
L. lepidophyllaceus
L. levidensis
L. linearis
L. longifolius
L. longiformis
L. macrolepis
L. major
L. mintoensis
L. moyseyi
L. muelleri
L. nemejcii
L. oblongifolius
L. oblongiformis
L. ornatus
L. ornatus
L. pachyrhachis
L. parvulus
L. pinaster
L. princeps
L. radians
L. richardsonii
L. ronnaensis
L. russellianus
L. senkevitschiae
L. silesiacus
L. squamosus
L. stachyoides
L. stephanicus
L. takhtajanii
L. tenuis
L. tevelevii
L. thomasii
L. undulatus
L. variabilis
L. weberensis
L. wuenschianus
L. wufengensis
L. xinjiangensis
L. yabei
L. zalesskyi
L. zeilleri
Lycospora †
Lycospora †
Microspore, with male gametophytes
Oxroadia †
Oxroadia †
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 resembles a compact Stigmaria
Above: Reconstruction of Oxroadia from Wyman et al., 2025, Fig. 4A
Otzinachsonia beerboweri †
Otzinachsonia beerboweri †
Cressler & Pfefferkorn, 2005
Famennian of Pennsylvanian
Cormose (swollen) four-lobed base with masses of attached rootlets
The stems exhibited a spiral arrangement of elliptical leaf scars without leaf cushions
Above: Otzinachsonia beerboweri. Photo by Walt Cressler.
Protolepidodendropsis pulchra †
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 †
Protostigmaria eggertiana †
Cormose rooting organ with multiple lobes
Above: In-situ Protolepidodendropsis † fossils (From Fig 4, Berry & Marshall 2015
Ulodendron †
Sigillaria †
Sigillaria †
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 & 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
Stigmaria †
Stigmaria †
Root-like rhizomorph (modified rhizome-like stem that anchors and absorbs water/minerals)
Sublepidophloios †
Sublepidophloios †
Synchysidendron †
Synchysidendron †
Additional Resources
Additional Resources
The root of the problem: Ancient trees may have grown their roots backwards (ScienceX 5May2026)
└A shoot at the root? Unique development and evolution of the stigmarian apical meristem (D'Antonio et al., 2026)
The Rise and Fall of the Scale Trees (In Defense of Plant, 2018)
Scale trees (Hans Steur Fossil Plant webpage)
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