Protolepidodendrids
Clubmosses with branched microphylls
Plants in the Protolepidodendrales are from the Middle Paleozoic, and may be the ancestors of the enormous scale trees during the Carboniferous. One defining feature is that these herbaceous plants had forked or brancheleaves, which is unique among clubmosses.
Ecology & Form
Stems
Herbaceous or sub-woody with isotomous and anisotomous branching;
Prostrate rhizome was probably indeterminate
Leaves
Branched microphylls for leaves
No other lycophytes display forked leaves
Some leaves have a ligule
Classification
└Protolepidodendrales †
Geologic Age
Diversity
Archaeosigillariaceae
Archaeosigillaria †
A. vanuxemii † (Vanuxem 1842; Grierson & Banks 1963)
Leaves 5-6 mm long, simple, possibly petiolate, with a deltoid lamina that bears three or four opposite pairs of small serrations and tapers to an acute apex tipped by a tiny hair (Senkewich, 1956; Fairon-Demaret & Banks, 1978).
Stems are regarded as characterized by hexagonal patterns produced by subepidermal thick-walled cells that surround the areas of attachment of leaves
Gilboaphyton †
G. goldringiae † (Arnold 1937; emended Berry and Edwards 1996)
Dichotomous branching.
Leaves spirally-arranged, their enlarged bases forming broadly fusiform to hexagonal patterns delimited by narrow grooves.
Persistent leaves laminar, divided into a large medial segment and two substantially smaller and shorter distal-pointing opposite lateral segments about midway along the total leaf length.
Protostelic xylem column lobate in outline, exarch.
G. griersonii † Berry and Edwards 1996
"no younger than Frasnian, and no older than late Eifelian"
Vegetative stems, 8-14.5 mm diameter, and up to at least 11 cm in length, bifurcating probably isotomously.
Stem surfaces divided into spirally arranged, adjoining, longitudinally elongate hexagonal or fusiform swollen leaf bases; 7-8 bases per horizontal turn, separated by narrow grooves, each bearing a persistent leaf just above its center.
Leaves slender, upright, up to 9 mm long and 1.20-1.49mm wide with broad base, divided approximately halfway along their length to give a narrow central segment and two much shorter lateral upwards-pointing segments, all tips acute.
Cortex differentiated into layers, Outer zone of stem tissues most resistant to decay, containing elongate regions of softer tissues seated within the leaf bases connected to a cylinder of similar tissue associated with the leaf trace.
Atasudendraceae
Atasudendron †
Senkevitsch et al. 1993
Blasariaceae
Barrandeina
Stur 1882
Barrandeinopsis
Kristofovic 1955
Blasaria
Zalessky 1934
Broeggeria
Nathorst 1914-1915
Cyclostigmataceae
Cyclostigma
Haughton 1859
Knorria
Sternberg 1825
Jurinodendron
Doweld, 2001 †
Eleutherophyllaceae
Eleutherophyllum
Stur 1877
Zimmermannia
Gothan & Zimmermann 1932
Lepidosigillariaceae
Lepidosigillaria
Kräusel & H. Weyland 1949
Genus Libyaria
Lejal-Nicol 1975
Leptophloeaceae
Omphalophloiaceae
Protolepidodendraceae
Leclercqia †
L. andrewsii (Gensel and Kasper 2005)
L. complexa (Banks, Bonamo and Grierson 1972; Bonamo, Banks and Grierson 1988)
L. uncinata (Xu et al. 2011)
Axes branching isotomously or anisotomously at angles of 15–45
1.6–2.6 mm wide, at least 70 mm long
Leaf bases elongate-fusiform, tightly arranged in helices or pseudowhorls
8-10 leaves inserted on the axis per gyre
Leaf consists of a basal segment, dividing just below the midpoint into three major segments, a long narrow central segment, and two further divided opposite lateral segments arranged in three dimensions
Deflected abaxially, tapering distally and terminating in an abaxially tightly recurved hook
Pairs of lateral major segments are divided near the base into two or very often three more or less equal minor segments
Sporophyll similar in morphology to sterile leaf; no strobilus formed
Sporangium ovate to fusiform in lateral view, ovate in adaxial view, attached by an oval pad proximal to the division of the leaf,
Plant homosporous
Above: Reconstruction of Leclercqia complexa
Protolepidodendron †
There is debate whether Protolepidodendron is a valid genus. The Protolepidodendrales are plants that exhibit forked leaves. The holotype specimen of P. scharyanum (in Prague) is poorly preserved and possibly shows a forked leaf, but the apices of other leaves are missing.
P. scharyanum (Krejci 1880; Krausel & Weyland 1929; Jurina 2009)
Middle Devonian
The axis width is 3.1–3.3 mm and does not change over the entire specimen. Leaves with conical bases and narrowing
The length of fragmentary leaves is 2–3 mm, with a bifurcation approximately in its middle area (2 mm from the base) into two thin segments of apices about 2 mm long.
The apices are at an angle slightly exceeding 90° to each other.
Leaf scars are fusiform, acuminate at both extremities, about 2 mm long and 0.4–0.5 mm wide, are arranged in a very low spiral. There are three or, rarely, four leaf scars in each row.
Sublepidodendraceae
Artschaliphyton unicum †
Senkevich 1971 (originally called Gilboaphyton goldringae Arnold)
Herbaceous plants with isotomous or pseudomonopodial branching
Leaves are petiolate, permanent, hastate, possibly toothed margin
Leaf scars are circular to oval
Sporangia are unknown
Cervicornus wenshanensis †
Pragian compression fossil from Yunnan China
Herbaceous axes with leaves arranged in openly spaced helices
The distal portion of each of the leaves is divided three times, resulting in eight segments
Anatomy is not preserved.
Above: Holotype specimen (Plate 1) of Cervicornus
Clwydia decussata †
Leaves (originally called Archaeosigillaria kidstoni) are 12 mm in length with a rhomboid lamina whose upturned distal portion tapers into a long hair (Lacey, 1962). On younger axes the leaves are opposite decussate.
Artschaliphyton unicum †
Senkevich 1971 (originally called Gilboaphyton goldringae Arnold)
Herbaceous plants with isotomous or pseudomonopodial branching
Leaves are petiolate, permanent, hastate, possibly toothed margin
Leaf scars are circular to oval
Sporangia are unknown
Colpodexylon †
Axes up to 2.5cm wide with isotomous branching
Lobed protostele with exarch maturation; no secondary xylem
Leaf cushion lacking scars or markings
Leaves are persistent and up to 3 cm long, and 3-forked
Sporangia adaxial and below the forking
C. deatsii †
Frasnian (Late Devonian)
C. gracilentum †
Dou et al. 1983; Xu & Wang 2011
Middle Devonian of NW China
C. pullumpedes †
Famennian of Waterloo Farm, South Africa
‘Short-tipped’ species
High latitude taxon, probably living in refugia into the Late Devonian
C. mergae †
Famennian of Coombs Hill, South Africa
‘Long-tipped’ species similar to C. deatsii, but with different proportions
High latitude taxon, probably living in refugia into the Late Devonian
C. trifurcatum †
Eifelian (Middle Devonian)
Estinnophyton (?) †
E. gracile (Fairon-Demaret 1979)
E. wahnbachense (Kräusel et Weyland; Fairon-Demaret 1979)
Originally described as Protolepidodendron wahnbachense (Kräusel et Weyland 1932) from the Siegenian of Germany
Narrow axes with persistent leaves, which are bifurcated and spirally arranged.
The vegetative and fertile leaves bifurcate twice and the four resulting segments are spread in various planes
The fertile leaves support two pairs of stalked elongate sporangia which are directed towards the axis
E. yunnanense (Hao et al. 2004)
Lower Devonian (upper Pragian) Posongchong Formation at Zhichang village, Gumu Town, Wenshan District, Yunnan Province, China.
This plant possesses aerial stems with isotomous branching
The leaves are slender, once- or twice-bifurcated, and arranged in low spirals or pseudo-whorls
Fertile leaves are morphologically identical to the vegetative ones, clustered on the axis, forming a loose strobilus-like structure
There are three to six fertile leaves in each gyre
Two ovoid-elongate sporangia are singly attached to the adaxial surface each subtended by a recurved stalk, either at the base of each segment in a once-bifurcate fertile leaf or below the points of successive divisions in a twice-bifurcate fertile leaf
E. yunnanense differs from E. gracile and E. wahnbachense, mainly in possessing two single stalked sporangia on each fertile leaf rather than two pairs of sporangia, as well as in the dimensions of its leaves.
Estinnophyton is considered to have had a closer affinity with primitive sphenopsids than the protolepidodendralean lycopsids
Above: Line drawing of the fertile leaves of E. yunnanense
Haskinsia †
Three known species from the Middle Devonian
H. colophylla † (Grierson & Banks 1983) --> originally called Drepanophycus colophylla Grierson & Banks (1963)
H. hastata † (Berry & Edwards 1996)
H. sagittata † (Edwards & Benedetto 1985)
Middle Devonian
Stems are narrow and isotomous
Leaves are petiolate and helically-arranged
Leaf lamina is roughly deltoid in shape; H. hastata has hastate leaves and H. sagittata has sagittate leaves
During the Middle Devonian, Haskinsia was distributed in tropical, warm temperate and high southern latitude, cool (?) temperate zones (Cingolani et al. 2002)
Above, left: Reconstruction of Haskinsia colophylla growing on a Lepidosigillaria stump (from Retallack 2018); Above, right: leaves of H. sagittata and H. hastata (Berry & Edwards 1996)
Zhenglia radiata †
A small and slender herbaceous I ycopsid, possessing simple, entire, possibly ligulate microphylls, with decurrent, swollen bases
Rhomboid leaf bases, showing lepidodendroid-like phyllotaxic arrangement.
Leaf having a single vein.
Fertile structure consisting of closely arranged sporophylls.
Sporophylls basically identical with microphylls.
Each sporophyll bearing a single, ovoid-elongate sporangium attached adaxially.
Sporangia partly enclosed by lateral extensions of the sporophyll lamina.
Above: Zhenglia radiata † (Fig 2, Hao et al. 2006)