| Stigmaria | |
|---|---|
 | |
| Stigmaria, a fossil lycopsid rhizome | |
Scientific classification  | |
| Kingdom: | Plantae |
| Clade: | Tracheophytes |
| Clade: | Lycophytes |
| Class: | Lycopodiopsida |
| Order: | † Lepidodendrales |
| Genus: | † Stigmaria Brongn. |
Stigmaria is a form taxon for common fossils found in Carboniferous rocks. [1] They represent the underground rooting structures of arborescent lycophytes such as Sigillaria and Lepidodendron under the order Lepidodendrales.
The Paleozoic swamps had tree-like lycopsids that grew up to 30 m (98 ft), [2] and even 50 m (160 ft) in height. [3] These lycopsid plants were anchored by an extensive network of branching underground structures with root-like appendages attached to them. The underground organs or structures of these lycopsids is referred to as Stigmaria. [4] Lycopsids first evolved during a rapid diversification of terrestrial land plants in the Devonian period [5] and became common plants within the Carboniferous coal forest flora. Lycopsids grew in low-level swampy wetland areas which they flourished during the Pennsylvanian age. [6] [7] Analysis of the morphology and anatomy of the stigmarian systems suggests that the axes around the structure were shoot-like, and so they are called rhizomes or rhizomorphs. [8] In general, common species of Stigmaria (Stigmaria ficoides sp.) have been analyzed extensively to provide an understanding of its morphology and histology. [4]
The stigmarian systems had rhizomorph axes that presented circular scars around the rhizomorph apices of Stigmaria species, where the root-like appendages were attached to the circular scars. These appendages were branched dichotomously, meaning that there were multiple orders of branching functionality to comprise areas of the stigmarian system. Since the stigmarian systems were root-like, these lateral appendages indicate that these were modified leaves adapted to serve the function of the stigmarian system. Stigmaria had a complex branching structure; therefore, it is comparable to the rhizomes of the extant (living) relative, the quillworts (genus Isoetes). The stigmarian system extends leaning from the foundation of the stem as four proximal axes, leading to a hollow rooting structure. [8]
Along the rhizomorph axes, the appendages are linked to each axis in a circular pattern and would shed during the growth stage, forming the circular scars of Stigmaria. The lateral appendages have a circular layout, and the growth abscission is more distinctive of leaves than present lateral roots. 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 vary in size and do not dichotomize as they move further away from the central points of the axes. In terms of the position, each stigmarian rootlet has a vascular strand monarch which is surrounded by a condensed inner cortex. Externally, this inner cortex consists of a thin outer cortex and hollow middle cortex, and a network enlarges from the inner cortex to the outer cortex. [9]
Endarch is defined as the primary xylem of Stigmaria, and organized in forked vascular strands encompassed by vascular cambium. Tracheids of the secondary xylem are formed in spiral lines and consist of scalariform wall thickenings, while the fimbrils are similar to those in the aerial branches. The tracheids uniform to the stigmarian rhizomorph axes did not form vascular cambium, but dense meristem. [10]
Stigmaria development is linked to the changes in aerial stems found in typical rhizomic structures seen in present plants. Stigmaria's features are unrelated (in functionality) when linking to the functions of present plant roots and rhizomes. Moreover, the spiral structure of the stigmarian rootlet attachment is distinct to the unsymmetrical adjustment of roots and rhizomes typically 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 indicate that there is a similarity in the Lepidodendrales aerial structure system, and carries support to its stability features including absorbent organs, branching, and forking of proximal sectors of the axis. The linkage to the Lepidodendrales vascular plants proposes that the development and changes of the aerial shoot system including the stems existed among stigmarian systems. [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, it may be that the 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 lycopyhtes 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]
In vascular plants, the roots are the organs of a plant that are modified to provide anchorage for the plant and take in water and nutrients into the plant body, which allows plants to grow taller and faster. They are most often below the surface of the soil, but roots can also be aerial or aerating, that is, growing up above the ground or especially above water.
The lycophytes, when broadly circumscribed, are a group of vascular plants that include the clubmosses. They are sometimes placed in a division Lycopodiophyta or Lycophyta or in a subdivision Lycopodiophytina. They are one of the oldest lineages of extant (living) vascular plants; the group contains extinct plants that have been dated from the Silurian. Lycophytes were some of the dominating plant species of the Carboniferous period, and included the tree-like Lepidodendrales, some of which grew over 40 metres (130 ft) in height, although extant lycophytes are relatively small plants.
Lepidodendron is an extinct genus of primitive lycopodian vascular plants belonging the order Lepidodendrales. It is well preserved and common in the fossil record. Like other Lepidodendrales, species of Lepidodendron grew as large-tree-like plants in wetland coal forest environments. They sometimes reached heights of 50 metres, and the trunks were often over 1 m (3.3 ft) in diameter. They are often known as "scale trees", due to their bark having been covered in diamond shaped leaf-bases, from which leaves grew during earlier stages of growth. However, they are correctly defined as arborescent lycophytes. They thrived during the Carboniferous Period, and persisted until the end of the Norian around 208 million years ago. Sometimes erroneously called "giant club mosses", the genus was actually more closely related to modern quillworts than to modern club mosses. In the form classification system used in paleobotany, Lepidodendron is both used for the whole plant as well as specifically the stems and leaves.
In biology, stolons, also known as runners, are horizontal connections between parts of an organism. They may be part of the organism, or of its skeleton. Typically, animal stolons are exoskeletons.
Calamites is a genus of extinct arborescent (tree-like) horsetails to which the modern horsetails are closely related. Unlike their herbaceous modern cousins, these plants were medium-sized trees, growing to heights of 30–50 meters. They were components of the understories of coal swamps of the Carboniferous Period.
Equisetidae is one of the four subclasses of Polypodiopsida (ferns), a group of vascular plants with a fossil record going back to the Devonian. They are commonly known as horsetails. They typically grow in wet areas, with whorls of needle-like branches radiating at regular intervals from a single vertical stem.
The zosterophylls are a group of extinct land plants that first appeared in the Silurian period. The taxon was first established by Banks in 1968 as the subdivision Zosterophyllophytina; they have since also been treated as the division Zosterophyllophyta or Zosterophyta and the class or plesion Zosterophyllopsida or Zosteropsida. They were among the first vascular plants in the fossil record, and had a world-wide distribution. They were probably stem-group lycophytes, forming a sister group to the ancestors of the living lycophytes. By the late Silurian a diverse assemblage of species existed, examples of which have been found fossilised in what is now Bathurst Island in Arctic Canada.
Sigillaria is a genus of extinct, spore-bearing, arborescent lycophyte, known from the Carboniferous and Permian periods. It is related to the more famous Lepidodendron, and more distantly to modern quillworts.
In botany, secondary growth is the growth that results from cell division in the cambia or lateral meristems and that causes the stems and roots to thicken, while primary growth is growth that occurs as a result of cell division at the tips of stems and roots, causing them to elongate, and gives rise to primary tissue. Secondary growth occurs in most seed plants, but monocots usually lack secondary growth. If they do have secondary growth, it differs from the typical pattern of other seed plants.
Asteroxylon is an extinct genus of vascular plants of the Division Lycopodiophyta known from anatomically preserved specimens described from the famous Early Devonian Rhynie chert and Windyfield chert in Aberdeenshire, Scotland. Asteroxylon is considered a basal member of the Lycopsida.
The rhyniophytes are a group of extinct early vascular plants that are considered to be similar to the genus Rhynia, found in the Early Devonian. Sources vary in the name and rank used for this group, some treating it as the class Rhyniopsida, others as the subdivision Rhyniophytina or the division Rhyniophyta. The first definition of the group, under the name Rhyniophytina, was by Banks, since when there have been many redefinitions, including by Banks himself. "As a result, the Rhyniophytina have slowly dissolved into a heterogeneous collection of plants ... the group contains only one species on which all authors agree: the type species Rhynia gwynne-vaughanii". When defined very broadly, the group consists of plants with dichotomously branched, naked aerial axes ("stems") with terminal spore-bearing structures (sporangia). The rhyniophytes are considered to be stem group tracheophytes.
This page provides a glossary of plant morphology. Botanists and other biologists who study plant morphology use a number of different terms to classify and identify plant organs and parts that can be observed using no more than a handheld magnifying lens. This page provides help in understanding the numerous other pages describing plants by their various taxa. The accompanying page—Plant morphology—provides an overview of the science of the external form of plants. There is also an alphabetical list: Glossary of botanical terms. In contrast, this page deals with botanical terms in a systematic manner, with some illustrations, and organized by plant anatomy and function in plant physiology.
The Fossil Grove is a group of plant fossils located within Victoria Park, Glasgow, Scotland. It was discovered in 1887 and contains the fossilised stumps and the stigmarian system of eleven extinct Lepidodendron lycopsids, which are sometimes described as "giant club mosses" but are more closely related to quillworts. The Fossil Grove is managed as a museum and has been a popular tourist attraction since it opened for public viewing in 1890.
Lepidodendrales or arborescent lycophytes are an extinct order of primitive, vascular, heterosporous, arborescent (tree-like) plants belonging to Lycopodiopsida. Members of Lepidodendrales are the best understood of the fossil lycopsids due to the vast diversity of Lepidodendrales specimens and the diversity in which they were preserved; the extensive distribution of Lepidodendrales specimens as well as their well-preservedness lends paleobotanists exceptionally detailed knowledge of the coal-swamp giants’ reproductive biology, vegetative development, and role in their paleoecosystem. The defining characteristics of the Lepidodendrales are their secondary xylem, extensive periderm development, three-zoned cortex, rootlike appendages known as stigmarian rootlets arranged in a spiralling pattern, and megasporangium each containing a single functional megaspore that germinates inside the sporangium. Many of these different plant organs have been assigned both generic and specific names as relatively few have been found organically attached to each other. Some specimens have been discovered which indicate heights of 40 and even 50 meters and diameters of over 2 meters at the base. The massive trunks of some species branched profusely, producing large crowns of leafy twigs; though some leaves were up to 1 meter long, most were much shorter, and when leaves dropped from branches their conspicuous leaf bases remained on the surface of branches. Strobili could be found at the tips of distal branches or in an area at the top of the main trunk. The underground organs of Lepidodendrales typically consisted of dichotomizing axes bearing helically arranged, lateral appendages serving an equivalent function to roots. Sometimes called "giant club mosses", they are believed to be more closely related to extant quillworts based on xylem, although fossil specimens of extinct Selaginellales from the Late Carboniferous also had secondary xylem.
A stem is one of two main structural axes of a vascular plant, the other being the root. It supports leaves, flowers and fruits, transports water and dissolved substances between the roots and the shoots in the xylem and phloem, photosynthesis takes place here, stores nutrients, and produces new living tissue. The stem can also be called halm or haulm or culms.
Adoketophyton is a genus of extinct vascular plants of the Early Devonian. The plant was first described in 1977 based on fossil specimens from the Posongchong Formation, Wenshan district, Yunnan, China. These were originally named Zosterophyllum subverticillatum; later the species was transferred to a new genus as Adoketophyton subverticillatum. One cladistic analysis suggested that it is a lycophyte, related to the zosterophylls. Other researchers regard its placement within the vascular plants as uncertain.
Discalis is a genus of extinct vascular plants of the Early Devonian. The name is derived from the Greek δίσκος, referring to the disc-shaped sporangia. The genus was first described by Hao in 1989 based on fossil specimens from the Posongchong Formation, Wenshan district, Yunnan, China.
Nothia was a genus of Early Devonian vascular plants whose fossils were found in the Rhynie chert in Scotland. It had branching horizontal underground stems (rhizomes) and leafless aerial stems (axes) bearing lateral and terminal spore-forming organs (sporangia). Its aerial stems were covered with small 'bumps' (emergences), each bearing a stoma. It is one of the best described early land plants. Its classification remains uncertain, although it has been treated as a zosterophyll. There is one species, Nothia aphylla.
Archaeopteris macilenta is distinguished from other species of the genus by leaves which are divided into narrow segments at their tips. Sporangia were borne on different parts of the branches with ordinary foliage leaves. Archaeopteris macilenta leaves and fertile shoots are attached to wood which when permineralized is called Callixylon newberryi. Archaeopteris is retained in the class Progymnospermopsida which includes plants with gymnospermous anatomy and pteridophytic reproduction.
Leptophloeum is an extinct genus of vascular plants in the lycophyte clade. It is widely distributed being, known from the Laurasian and Gondwanan settings between the Devonian and Early Carboniferous periods.
