Lycopods
(or Clubmosses)
Class Lycopsida
Lycopods are a group of living and extinct plants that were hugely successful during the Paleozoic Era. Living representatives include ground pines, quillworts, and spikemosses. Scale trees, an extinct group of tree-sized lycopods, formed some of the first swamp forests on the Earth, dominating during the Carboniferous Period. Today lycopods are small plants with moss-like leaves, called microphylls. Because of their stature and leafy appearance, some people confuse this group for true mosses. Unlike mosses, lycopods are vascular plants, and they exhibit dichotomous branching. They have spore cases that sit ontop (adaxial) of specialized leaves called sporophylls. These sporophylls are usually clumped together to create a cone with a club-like appearance. The moss-like leaves combined with the club-like cones is how they they got the name "clubmoss".
Diversity
The Lycopsida includes both extinct (†) and extant groups:
* Diverts to the Plant Diversity site
Ecology & Form
Sporophyte (spore-bearing phase)
Stems
Morphology
Dichotomous branching: Isotomous generally in ancestral taxa, and anisotomous branching in derived forms
Some taxa display anistomy in proximal portions of the plant, and isotomous branching in the distal branches
Anatomy
Protostele in herbaceous forms, with haplosteles, actinosteles, and plectosteles found in different lycopod groups
In some large Paleozoic forms, such as the scale trees (Lepidodendridales), there was cambium that produced wood (secondary xylem), as well as a cork cambium that produced bark
The living quillwort, Isoetes, which is the closest relatives to the scale trees, still produced tiny amounts of wood in their corm
Leaves
The lycopods are the earliest plant group to produce leaves (e.g. Bara
Their leaves are called lycophylls or microphylls,
In many lycopod groups the leaves are helically-arranged on the stem (e.g. Lycopodiales, Lepidodendrales), but the Selaginellales have evolved to exhibit a planated
Roots
Adventitious roots, sometimes from root-like stems called rhizophores
Reproductive Structures
Sporangia associated with a leaf (=sporophyll) and frequently clustered into cones or strobili for many species
Sporangia located on the adaxial (top) surface of sporophyll (contrast this with the abaxial position for ferns)
Homosporous sporangia in ancestral groups (e.g., Huperzia, Lycopodium)
Heterosporous in derived groups (e.g., Selaginella, Isoetes)
Gametophyte (gamete-bearing phase)
The gametophytes of lycophytes may be non-photosynthetic or photosynthetic
Classification
└Lycopsida
Geologic Range
Late Silurian - present
Above: Huperzia selago, a clubmoss in the Lycopodiaceae
Additional Resources
Ferns of the World: a comprehensive list of living lycophytes
Incertae sedis
Atasudendron mirum †
Senkevich et al., 1993
Late Middle Devonian of Kazakhstan
Originally called Mixostrobilus givetensis
Stems up to 100 mm wide and 1–2 m tall
Sporophylls are simple and entire
Strobili are bisporangiate
Sporangia are stalked
Microspores are elongate to ellipsoidal, 40–76 µm in size
Megaspores 480–650 µm in size
Chamaedendron multisporangiatum †
Schweitzer & Li, 1996; Wang & Berry, 2003
Upper Devonian (Frasnian) of Hubei province
Up to 7 mm wide and 0.5 m in height
Stems with isotomous branching and lack secondary tissues
Sporophylls spindle-shaped, with dentate margins; sporophylls with an enlarged proximal region crudely protecting the sporangium
No strobilus observed
On the fertile leaves observed structures were interpreted as 4-6 megasporangia (800 x 600 um) and up to 12 microsporangia (750 x 225 um)
Megaspores about 750 µm in size
Hueberia zhichangensis †
Plant with vegetative creeping and erect stems and dichotomous branching that occurs at irregular intervals producing clustering in the creeping stems.
Most stems crowded with falcate enations inserted in a helical phyllotaxis.
Stems 1.3-1.8 mm wide.
Enations 0.6-1.0 mm wide and 0.9-1.6 mm long, with the angle of insertion on the axes varying from 30° to 80° (most between 40° and 60°).
Enations arranged in a regular helix with 6 to 8 per gyre and are more closely spaced distally.
The spacing between two gyres is about 1 mm.
Above: Hueberia zhichangensis † (Plate I, Yang et al. 2016)
Hoxtolgaya robusta †
Homosporous, arborescent lycopsid, which is unique compared to other Devonian-Carboniferous tree-like clubmosses
Leaf bases fusiform, tightly arranged in a pseudowhorled fashion
Leaf persistent, long linear with a middle vein from the basal and minute teeth in the basal margins
Fertile zone without specialized strobili
Isomorphic sporophyll curving downwardly from the basal
Sporangium oval in shape, attaching to the sporophyll by a pad
Above: Hoxtolgaya robusta † (Fig 4, Xu et al. 2012)
Kossoviella timanica †
Petrosjan, 1984, Orlova & Zavialova, 2018
Heterosporous lycopsids with erect, dichotomously divided axes covered with leaves without a ligule
Leaves with smooth margins, linear, rarely lanceolate, with a single vein.
Leaves in tight spiral or in pseudo-whorls
Leaf bases fusiform.
Strobili bisporangiate
Megasporangia in proximal-middle part
Microsporangia in middle-distal part of strobilus
Sporadic megasporangia and microsporangia occur at the same level on opposite sides of the axis in the transition zone
Sporophylls lanceolate, with spoon-like base and crenulated margins
Each sporophyll bears a single adaxial, sessile sporangium
Megasporangia large, with usually destroyed sporangial walls and with four to eight trilete megaspores
Microsporangia globose, ovoid, with numerous tetrads of rounded-triangular, trilete microspores
Above: Kossoviella timanica † sterile axes and strobil (From Fig 2, Orlova & Zavialova 2018)
Longostachys latisporophyllus †
Cai & Chen, 1996; Zhu et al.
Middle Devonian (Givetian) of Hunan Province
Longostachys has a pseudobipolar growth habit, with a downward-directed dichotomizing rooting system (lacking rootlets) and an upward-directed trunk with a crown of upward-pointing isodichotomous branches with terminal cones.
It reached an estimated height of 1.5 m.
Sporophylls with spoon-like, spiny appendages
Sporangia are sessile and ellipsoidal with Laevigatisporites-type megaspores
Lycopodolica tsegelnjucki †
Ishchenko, 1969
Late Silurian (Pridoli) of Ukraine
Plants there are preserved as compressions without internal detail.
Lycopodolica had stems (axes) which appear to have branched and which are covered with lax, hair- or thread-like outgrowths
Lycopodolica differs from Baragwanathia in the nature of its outgrowths or enations
Some researchers consider it a lycopsid (Hao and Xue 2013)
Monilistrobus yixingensis †
Upper Devonian (Famennian) of the Wutung Formation, Jiangsu, China.
Small lycopsid with isodichotomous branching,
Helically-arranged obovate expanded leaf bases, linear leaves with spiny appendages along the lateral margins
Sporophylls widened proximally, and one elliptical sporangium attached to the adaxial surface
Ellipsoid sporangia borne singly on the adaxial surface; compacted into cone-like structures borne on the axes, both terminal and intercalary, including at dichotomies of the axes, and spaced along the axis separated by lengths of more distantly spaced sterile leaves
The most distinctive novel feature of the plant is that the modified sporophylls are arranged tightly into fertile zones or cone-like structures that are separated by lengths of axes with more lax sterile microphylls only
Therefore, the cone-like structures are strung along the branches like beads on a necklace
Above: Monilistrobus yixingensis (from Fig 5, Wang & Berry 2003)
Wuxia bistrobilata †
Late Devonian (Famennian) of Wuxi, Jiangsu Province, China
Isodichotomous branches and long leaves with spiny margins
Two types of fertile structures are present
Megasporangia-bearing conelike structures are found at dichotomies of the branches, having large, densely inserted leaves with enlarged bases, bearing adaxial sporangia containing large megaspores
The other type are terminal cones, having slender, closely inserted leaves, and dark carbonaceous areas adjacent to the axis are interpreted as the remains of microsporangia
The new plant closely resembles lycopsids previously reported from the Middle and lower Upper Devonian of China, but the reproductive characters are more advanced
It demonstrates that the early history of large lycopsids is more complex than has been recognized
Above: Wuxia bistrobilata (Fig. 5 Berry et al. 2003)
Additional Resources
A consistent genetic structure in lycophytes for over 350 million years (Phys.org 19Jan2023)
└Li et al. (2023) Extraordinary preservation of gene collinearity over three hundred million years revealed in homosporous lycophytes