Sigillariaceae
| Sigillariaceae | ||||||||||||
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Sigillaria sp. |
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| Temporal occurrence | ||||||||||||
| Carbon to Permian | ||||||||||||
| 359 to 251 million years | ||||||||||||
| Systematics | ||||||||||||
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| Scientific name | ||||||||||||
| Sigillariaceae | ||||||||||||
The Sigillariaceae are a family of extinct club moss plants that grow predominantly in the shape of trees and that were part of the coal swamps in the Carboniferous . Well-known fossils from this family are the trunks of the genus Sigillaria, also known as seal trees .
features
The distinguishing features ( synapomorphies ) that distinguish the Sigillariaceae from the other families of the order are: the leaf traces arise from two protoxylem strands; the periderm contains bands of "resinous" cell aggregates; to see the periderm massive Parichnos strands; each leaf is supplied by two xylem strands that form a pair of central bundles; on the leaf there is a central pit adaxially; the ornaments of the microspores are prickly-conical. Features that the family shares with individual other representatives of the order are: the cone stems or the cone-bearing side branches sit on the main stem; the periderm is "resinous"; the ratio of leaf cushion height to width is 1: 1 or smaller on side branches; there are paired abaxial pits on the leaf.
Vegetative characteristics
The Sigillariaceae are tree-shaped plants, few and only distally branched, and smaller than the related Lepidodendraceae . Most representatives stayed under 20 m high, even if individual specimens were over 30 m high. A characteristic feature are the leaf bases , which are hexagonal in outline, more rarely elliptical, and have led to the name "seal tree". They are arranged helically on the trunk, but often seem to be in vertical rows. The actual leaf scar is usually elliptical, in the middle sits the leaf track scar that of two large Parichnos flanked -Narben. The vascular bundle is V-shaped and sometimes divided into two strands. The scar of the ligula sits above the leaf scar .
- leaves
The Sigillariaceae had leaves only at the ends of the stem axes, where they were close together. The long leaves are partially traversed by two laterally flattened vascular bundles. This feature distinguishes the leaf genera Sigillariophyllum and Sigillariopsis from representatives of the Lepidodendraceae , while they were otherwise quite similar. There are two longitudinal furrows on the underside of the leaf, which are covered with conspicuous trichomes . The stomata are arranged in rows, the escort cells have sunk. Cyperites is a genus of isolated leaves that are more than 1 cm wide and have a butterfly-shaped or x-shaped cross-section.
- tribe
While compression fossils from the Carboniferous are very common, structurally preserved shoot axes are quite rare. The center of the stem consists of parenchymal marrow surrounded by a continuous band of primary xylem . In cross-section, the outer edge of the exarch primary xylem appears wavy, with the leaf marks arising in the furrows. The tracheids of the metaxylema have fimbrillen between the bars of the ladder-like bars. Little secondary xylem is formed, which consists of ladder tracheids and narrow wood rays. The distribution of the bark tissue is similar to that of the related genus Diaphorodendron , tangentially banded periderm is common. In the periderm there are concentric bands of - probably - secretion cells. Pairs of cylindrical or laterally flattened strands of Parichnos tissue pass radially through the periderm. It is related to the Parichnos scars of the leaf bases and possibly acted as ventilation tissue.
Fossils in the debarked state are summarized in the form genus Syringodendron . Their surface shows vertical rows of large, often double-elliptical scars that resemble rabbit tracks. These are Parichnos strands in a tangential section.
- Underground organs
The underground organs of the Sigillariaceae are essentially similar to the stigmaria of the other Lepidodendrales, but there are some anatomical differences. The pith is relatively narrow compared to the diameter of the stele . It consists of an inner zone of pure parenchyma and an outer zone where parenchyma and tracheids occur together. The bark is relatively narrow and consists of two primary zones. The secondary growth of the cortex occurs through two concentric rings of meristems in the outer cortex. The form genus Stigmariopsis includes subterranean organs that are assigned to the subgenus Subsigillaria . They differ from Stigmarien by their unequal branching, with the smaller side branch pointing downwards.
Reproductive organs
Sigillaria was heterospore , so it produced spores of different sizes . The cones, however, were monosporangiate, so each formed only one of the two types of spores. The cones stood between the leaf bases.
Mazocarpon oedipternum from the late Pennsylvania of North America consists of cones with a diameter of 1.2 cm and a length of often 10 cm. The sporophylls are arranged in a flat screw or in pseudo whorls. The distal end of a sporophyll is rather short. The megasporangia are roughly triangular, they contain a central parenchymatic cushion surrounded by eight megaspores. The megaspores are large and trilet (have a three-pointed scar). Short archegonia necks protrude from their proximal suture .
The microspore-bearing cones, also included in the genus Mazocarpon , contain trilateral spores about 60 micrometers in diameter. Late Pennsylvania Mazocarpo villosum is 2.2 cm in diameter.
The mega gametophytes are known from several species . They consist of prothallium tissue and rhizoids , their archegonia are up to 65 micrometers in size with three layers of cervical cells.
In their reproduction, the Sigillariaceae were quite diverse with three ways of megasporic spread:
- The spores developed rapidly and were released from the sporangium. The representative is Mazocarpon villosum .
- The sporophylls remain on the cone at maturity, the megaspores are scattered when the sporangia wall ruptures. Representatives is about Mazocarpon oedipternum .
- The megaspores were expanded with their sporophylls by disintegrating the cones. Representatives are Mazocarpon pettycurense and Mazocarpon cashii .
Sigillariostrobus are compression fossils of cones up to 30 cm in length. They are likely to be another form of mazocarpon .
Systematics
The Sigillariaceae are the sister group of the group Lepidodendraceae + Diaphorodendraceae .
The form and arrangement of the leaf bases were used for the systematic classification within the genus Sigillaria . There are the following sub-genres and sections:
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Sigillaria subg. Eusigillaria has ribbed trunk surfaces .
- In the section Rhytidolepis , the leaf bases and the ribs are separated, the furrows between adjacent ribs are straight or almost straight.
- In the section Favularia , leaf bases and ribs are close together, the furrows are zigzag.
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Sigillaria subg. Subsigillaria has no ribs.
- Section Leiodermaria has vertical rows of leaf scars standing far apart from one another without raised leaf cushions.
- In the section Clathraria the leaf bases are close together.
Temporal and spatial distribution
The Sigillariaceae had their heyday in the late Pennsylvania . They grew in areas near the swamp, which were somewhat drier than the locations of the other tree-shaped club moss plants.
supporting documents
- William A. DiMichele, Richard M. Bateman: The Rhizomorphic Lycopsids: A Case-Study in Paleobotanical Classification . Systematic Botany, 1996, Vol. 21, pp. 535-552.
- 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. 303-307.
