Stigmaria
Stigmaria | |
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Stigmaria, a fossil lycopsid rhizome | |
Scientific classification | |
Kingdom: | Plantae |
Clade: | Tracheophytes |
Clade: | Lycophytes |
Class: | Lycopodiopsida |
Order: | †Lepidodendrales |
Genus: | †Stigmaria Brongn. |
Stigmaria is a
Description and morphology
Overview
The
Appendages ("rootlets")
Stigmaria had a complex branching structure; thus, it is comparable to the rhizomes of the extant (living) relative, the quillworts (genus Isoetes). The stigmarian systems had rhizomorph axes that shows circular scars or a helical arrangement where the root-like appendages were formerly attached. These appendages were branched dichotomously, establishing the root abscission areas of the stigmarian system. Since the stigmarian systems were root-like, the lateral appendages indicate that they were modified leaves adapted to serve the function of abscission. Along the rhizomorph axes, the appendages are connected to each axis in a circular pattern which would shed during the growth stage, forming the helical arrangements of Stigmaria root abscission areas.[8]
Stigmaria consists of four proximal axes connected to the trunk of arborescent lycophytes. The four proximal axes dichotomize, creating a long underground system ranging up to 15 m (49 ft) in radius, while being up to 40 cm (16 in) long and 0.5–1 cm (0.20–0.39 in) wide. The stigmarian rootlets consist of monarch vascular bundle enclosed by the inner and outer cortex. Evidently, the inner cortex and outer cortex is anchored by a hollow middle cortex, and a network of vascular branches extends between them.[9]
Development
Stigmaria development is linked to the changes in aerial stems found in typical rhizomic structures seen in present plants. Stigmaria's features are unrelated when connecting to present plant functionality. Moreover, the spiral structure of the stigmarian rootlet attachment is separate from the asymmetrical changes of roots and rhizomes commonly seen in modern plants. While there were lateral appendages in Stigmaria, none were found in the root systems of modern plants. However, fungi has mycorrhizae, which are functioned from cortical parenchyma cells.[11]
Though vascular bundles in leaves are bilaterally symmetrical including the appendages of Stigmaria and the monarch vascular bundle, present rhizomes have a radial point of symmetric vascular tissues. Furthermore, within a certain growth stage, foliar abscission (active shedding) of the appendages occurs from the stigmarian axis. Nonetheless, root abscission is relatively absent in modern plants. The stigmarian rootlets have a similarity to arborescent lycophytes, with functions related to absorbent organs, branching, and forking of proximal axes.[12]
Since many lycopsids from the Paleozoic had a height of up to 50 m (160 ft) meters, and grew in unsteady engulfed and saturated soil, the lycopods and their stigmarian system grew around the river systems.[3][13] Therefore, it is debatable to how the underground system could handle the plants. Evidence to support their height was compared to the extensive stigmarian system. Thus, progression of the rhizomorph axes appeared to have secondary growth in their growth stages of the cortex. They may have been preferred to stand upright since arborescent lycophytes had bushy branches and only a few secondary xylem. The branches of neighboring lycopsids could interweave and deliver foundational support to the base stem.[11] On the other hand, the branch density and development of the wood in present trees can prevent uprooting.[14]
Gallery
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Bedding plane view of a flattened Stigmaria preserved atop a shallow-water carbonaceous limestone. Joggins, Nova Scotia, Canada.
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In situ Stigmaria fossil from the Joggins Formation (Pennsylvanian), Cumberland Basin, Nova Scotia, Canada
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In situlycopsidwith attached stigmarian system from Joggins, Nova Scotia, Canada
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Stigmaria impression with visible rootlets connecting from the rhizome
References
- JSTOR 2443571.
- . Retrieved 13 January 2024.
- ^ a b V. V. Alekhin (1961). Geografiia rastenii s osnovani botaniki (Geography of plants and basics of botany). Gos. nauchno-pedagog. izd-vo. p. 167. Retrieved 2020-10-05.
- ^ a b Williamson, William Crawford (1887). A monograph on the morphology and histology of Stigmaria ficoides. Vol. 40. Palaeontographical society.
- S2CID 244048051. Retrieved 25 November 2023.
- ^ Cleal, C. J. & Thomas, B. A. (2005). "Palaeozoic tropical rainforests and their effect on global climates: is the past the key to the present?" Geobiology, 3, p. 13-31.
- ISBN 0-901702-53-6.
- ^ PMID 27226309. Retrieved 15 February 2017.
- JSTOR 43235190.
- .
- ^ ISBN 9780226586311.
- ^ Frankenberg, Julian M.; Eggert, Donald A. (1969). "Petrified Stigmaria from North America: Part I. Stigmaria ficoides, the underground portions of Lepidodendraceae". Palaeontographica Abteilung B. Schweizerbart'sche Verlagsbuchhandlung: 1–47.
- doi:10.1038/ngeo1237.
- ISSN 0016-7061.