Protolepidodendrales
| Protolepidodendrales | ||||||||||||
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Leclercqia complexa |
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| Temporal occurrence | ||||||||||||
| Devon to Mississippium | ||||||||||||
| Systematics | ||||||||||||
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| Scientific name | ||||||||||||
| Protolepidodendrales | ||||||||||||
The Protolepidodendrales are an extinct group of club moss plants (Lycopodiopsida) and occurred from the Devonian to the Lower Carboniferous . The best known genus is Leclercqia .
features
The representatives were herbaceous plants , slightly woody or small trees. They had small, helically arranged microphylls , which were supplied by a single vascular bundle and were branched at the tip. A ligula is only known from one genus , but is absent from all other representatives.
Representative
Several dichotomously branched forms from the middle Devonian are grouped under the name protolepidodendron . The stem axes have a diameter of up to two centimeters and are covered with helically arranged microphylls, which are forked in two at the top.
Minarodendron cathaysiense was first as Protolepidodendron described. The finds have a diameter of 3 to 4 mm. They have longitudinal rows of elongated pillows on which the leaves sit. The tip of each leaf is forked into three parts, with the two lateral tips pointing upwards and the middle one pointing downwards. The trunk has an exarch or mesarche strand of primary xylem that is serrated or triangular in cross-section. The sporangia are spherical to kidney-shaped and are adaxially to the surface of unmodified sporophylls .
Estinnophyton - earlier also listed as protolepidodendron - are, like Estinnophyton gracile , small, herbaceous plants with stem axes of around 4 mm in diameter. The helically arranged leaves are up to 7 mm long. Sporophylls carry two pairs of sporangia, each on a short stalk. Estinnophyton yunnanense from Lower Devonian China has two single, stalked sporangia per leaf. While the forked leaves refer to the protolepidodendrales, the paired sporangia are more a feature of the trimerophytes .
Colpodexylon deatsii is a fairly well preserved species from the Middle and Upper Devonian of New York . The shoot axes are dichotomously branched and up to 2.5 cm thick. The leaf bases are elliptical, their arrangement a flat screw or a pseudo whorl . The leaves are forked into three parts and up to 3 cm long. The sporangia sit on the upper surface of normal leaves.
Clwydia (formerly Archaeosigillaria ) is a small, herbaceous, dichotomous branched representative, which is known from the Devonian and Carboniferous. The leaf bases are spindle-shaped on smaller axes and hexagonal on larger ones. Their helical arrangement appears cross-opposite . Some species have needle-shaped leaves, in Clwydia vanuxemii they are deltoid with a serrated edge, the tip ends in a long hair. The leaves of the genus probably did not fall off. The vascular system of the axes is a lobed protostele with an exarchic primary xylem and stair tracheids in the metaxylem.
Hubeiia dicrofollia is an herbaceous representative from the Upper Devonian of Hubei . The protoxylem is located on ribs on the outside of the stele and consists of ring tracheids . The metaxylem consists of stair tracheids , the stairs are connected by the longitudinal trabeculae (fimbrilles) that are otherwise typical of the Lepidodendrales . The primary phloem forms a narrow band around the stele. The bark is quite thick. The leaf marks are mesarchic and arise directly from the protoxylem. The leaf bases are circular or slightly elliptical and are arranged in flat screws or pseudo whorls . The leaves are divided into four segments by two consecutive dichotomies.
Wuxia bistrobilata from the Upper Devonian China has shoots up to 1.4 cm thick, the sterile leaves sit in groups of six in whorls. In the dichotomous branches of the rungs sit megasporangiate structures, which consist of elongated megasporophylls with a distinct midrib. There are irregular spines on the megasporophyll. The megaspores are up to 4 mm in size. Morphologically, it is most similar to Minarodendron cathaysiense .
Chamaedendron multisporangiatum , whose megasporophylls each carry four to six megasporangia, also comes from the Devonian of China . The microsporangia of this species are stalked and contain spores of the Longhuashanispora type. Chamaedendron is reconstructed as a narrow, tree-like plant with no secondary xylem.
Longostachys latisporophyllus from the Central Devon of China is also reconstructed as a small tree. The megasporophylls are elongated, the distal part is curved upwards, the leaf margin has trichome- like appendages. The species is regarded as an intermediate form between the herbaceous Protolepidodendrales and the tree-shaped Lepidodendrales.
Zhenglia radiata from the Lower Devonian of southeast Yunnan is also considered to be a transitional form to the Lepidodendrales. Your microphylls are undivided, the sporophylls are screwy and form a compact zone that resembles a cone. The ovoid-elongated sporangia sit adaxially on the widened, proximal part of the sporophyll. The arrangement of the leaf scars is similar to that of the Lepidodendrales.
Protolepidodendropsis pulchra from the Middle and Upper Devonian of Spitsbergen is tree-shaped and has a trunk diameter of up to 10 cm, the height is estimated at 1.5 to 2 m. The trunk surface is covered with helically arranged, wide-rhombic leaf cushions. Their size depends on their position on the trunk, with a size of 1.5 × 1.2 cm in the lower area. The clear leaf scar is located in the middle of the leaf cushion. Parichnos -Narben and Ligula Pit missing. The trunks branch dichotomously up to five times and thus form a loose crown. The leaves are narrow and simple. Protolepidodendropsis frickei from Upper Devonian Silesia was probably herbaceous.
supporting documents
- Thomas N. Taylor, Edith L. Taylor, Michael Krings: Paleobotany. The Biology and Evolution of Fossil Plants . Second Edition, Academic Press 2009, ISBN 978-0-12-373972-8 . Pp. 271-279.