Nothia
Encyclopedia
Nothia was a genus of Early Devonian
vascular plant
s 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, N. aphylla.
), were first described by Kidston and Lang in 1920 from the Rhynie chert
of Aberdeenshire, Scotland – rocks which are of Pragian age . The fragments were considered to be parts of Asteroxylon
mackiei. In 1964 Lyon described sporangia belonging to Asteroxylon mackiei and suggested that Kidston and Lang's specimens were a new species which he called Nothia aphylla. The first full description based on further specimens was published in 1979. A very detailed description was published in 2001, making this species one of the best-known early polysporangiophyte
s.
of Nothia aphylla consisted of thin underground and aerial stems (axes). The underground stems or rhizomes were up to 2 mm in diameter and branched laterally. The underside of the rhizomes had a longitudinal ridge from which unicellular rhizoid
s emerged. There were no true roots. At intervals the rhizomes turned upwards to emerge as upright stems. Around the region of the upwards bend, horizontal branches appeared at right angles to continue the growth of the rhizomes. The upright stems were generally less than 2.5 mm in diameter; a reconstruction suggests a height of around 20 cm. Aerial stems branched dichotomously in a three-dimensional pattern, with the last two sets of branches bearing sporangia. The sporangia were attached by short stalks at the end and along the sides of the stem, in a more-or-less spiral fashion. The stalks curved upwards so that the sporangia were roughly upright. Spores were released through a longitudinal slit which appeared at the apex of the sporangia. The spores were trilete and around 65 µm in diameter.
Both the horizontal rhizomes and the vertical stems had vascular tissue
which formed a central core (protostele), and is described as having centrarch development. The precise structure of the vascular core varied between the rhizomes and the aerial stems.
Although Nothia aphylla was leafless, its aerial stems were covered with 'emergences': bumps on the stems which were oval, around 0.3 mm high and 0.7 to 1.2 mm long by up to 0.5 mm wide. The emergences were formed by existing cells expanding, not by extra cells being produced as in other Early Devonian zosterophylls and trimerophytes. Each emergence had a single stoma
. The density of the emergences varied so that in regions which had them there were between 3 and 5 or more stomata per mm2. The sporangia did not have emergences, although there were a few stomata.
Kerp et al. suggest that Nothia aphylla was a geophyte which inhabited sandy soils and had a clonal life-style. The underground rhizomes persisted from year to year, continually spreading via lateral branches. The aerial stems appeared annually. They base this analysis on a number features, including evidence that the rhizomes were subterranean, and that rhizomes were still living when erect stems had decayed.
The plant described as Kidstonophyton discoides is possibly the male gametophyte
of Nothia aphylla.
since no description was published along with the name. Validation of the name has been variously considered to have been by Høeg in 1967, making the botanical authority
"Lyon ex Høeg", or by El-Saadawy and Lacy in 1979, making the authority "Lyon ex El-Saadawy & Lacy".
Nothia has been placed in the group initially established by Banks as the subdivision Zosterophyllophytina or the class Zosterophyllopsida
. El-Saadawy and Lacy regard the plant as having affinities with both the rhyniophytes and the zosterophylls. As discussed further below, Kerp et al. regard its taxonomic placement as unclear.
(living and extinct clubmosses and relatives).
A detailed study of Nothia aphylla questions this positioning of the genus, concluding that its taxonomic placement remains unclear, and that the cladistic analyses of Kenrick and Crane (on which the above cladogram is based) have ignored "fundamental differences" between different kinds of emergences (protrusions from stems). Features of the vascular tissue of typical zosterophylls, such as characteristic thickenings of the cells which conduct water, are also absent in Nothia. Earlier, El Saadawy and Lacey had concluded that Nothia was in some ways intermediate between the rhyniophytes and the zosterophylls.
Devonian
The Devonian is a geologic period and system of the Paleozoic Era spanning from the end of the Silurian Period, about 416.0 ± 2.8 Mya , to the beginning of the Carboniferous Period, about 359.2 ± 2.5 Mya...
vascular plant
Vascular plant
Vascular plants are those plants that have lignified tissues for conducting water, minerals, and photosynthetic products through the plant. Vascular plants include the clubmosses, Equisetum, ferns, gymnosperms and angiosperms...
s whose fossils were found in the Rhynie chert
Rhynie chert
The Rhynie chert is an Early Devonian sedimentary deposit exhibiting extraordinary fossil detail or completeness . It is exposed near the village of Rhynie, Aberdeenshire, Scotland; a second unit, the Windyfield chert, is located some 700 m away...
in Scotland. It had branching horizontal underground stems (rhizomes) and leafless aerial stems (axes) bearing lateral and terminal spore-forming organs (sporangia
Sporangium
A sporangium is an enclosure in which spores are formed. It can be composed of a single cell or can be multicellular. All plants, fungi, and many other lineages form sporangia at some point in their life cycle...
). Its aerial stems were covered with small 'bumps' (emergences), each bearing a stoma
Stoma
In botany, a stoma is a pore, found in the leaf and stem epidermis that is used forgas exchange. The pore is bordered by a pair of specialized parenchyma cells known as guard cells that are responsible for regulating the size of the opening...
. 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, N. aphylla.
History of discovery
Fossilized remains, including bare stems (axes) and detached spore-forming organs (sporangiaSporangium
A sporangium is an enclosure in which spores are formed. It can be composed of a single cell or can be multicellular. All plants, fungi, and many other lineages form sporangia at some point in their life cycle...
), were first described by Kidston and Lang in 1920 from the Rhynie chert
Rhynie chert
The Rhynie chert is an Early Devonian sedimentary deposit exhibiting extraordinary fossil detail or completeness . It is exposed near the village of Rhynie, Aberdeenshire, Scotland; a second unit, the Windyfield chert, is located some 700 m away...
of Aberdeenshire, Scotland – rocks which are of Pragian age . The fragments were considered to be parts of Asteroxylon
Asteroxylon
Asteroxylon is an extinct genus of plants of the Division Lycopodiophyta known from anatomically preserved specimens in an Early Devonian deposit of chert at Rhynie, Aberdeenshire in North-East Scotland that has been dated at...
mackiei. In 1964 Lyon described sporangia belonging to Asteroxylon mackiei and suggested that Kidston and Lang's specimens were a new species which he called Nothia aphylla. The first full description based on further specimens was published in 1979. A very detailed description was published in 2001, making this species one of the best-known early polysporangiophyte
Polysporangiophyte
Polysporangiophytes, also called polysporangiates or more formally Polysporangiophyta, are plants in which the spore-bearing generation has a structure of branching stems terminating in sporangia...
s.
Description
The sporophyteSporophyte
All land plants, and some algae, have life cycles in which a haploid gametophyte generation alternates with a diploid sporophyte, the generation of a plant or algae that has a double set of chromosomes. A multicellular sporophyte generation or phase is present in the life cycle of all land plants...
of Nothia aphylla consisted of thin underground and aerial stems (axes). The underground stems or rhizomes were up to 2 mm in diameter and branched laterally. The underside of the rhizomes had a longitudinal ridge from which unicellular rhizoid
Rhizoid
Rhizoids are thread-like growths from the base or bottom of a plant, found mainly in lower groups such as algae, fungi, bryophytes and pteridophytes, that function like roots of higher plants ....
s emerged. There were no true roots. At intervals the rhizomes turned upwards to emerge as upright stems. Around the region of the upwards bend, horizontal branches appeared at right angles to continue the growth of the rhizomes. The upright stems were generally less than 2.5 mm in diameter; a reconstruction suggests a height of around 20 cm. Aerial stems branched dichotomously in a three-dimensional pattern, with the last two sets of branches bearing sporangia. The sporangia were attached by short stalks at the end and along the sides of the stem, in a more-or-less spiral fashion. The stalks curved upwards so that the sporangia were roughly upright. Spores were released through a longitudinal slit which appeared at the apex of the sporangia. The spores were trilete and around 65 µm in diameter.
Both the horizontal rhizomes and the vertical stems had vascular tissue
Vascular tissue
Vascular tissue is a complex conducting tissue, formed of more than one cell type, found in vascular plants. The primary components of vascular tissue are the xylem and phloem. These two tissues transport fluid and nutrients internally. There are also two meristems associated with vascular tissue:...
which formed a central core (protostele), and is described as having centrarch development. The precise structure of the vascular core varied between the rhizomes and the aerial stems.
Although Nothia aphylla was leafless, its aerial stems were covered with 'emergences': bumps on the stems which were oval, around 0.3 mm high and 0.7 to 1.2 mm long by up to 0.5 mm wide. The emergences were formed by existing cells expanding, not by extra cells being produced as in other Early Devonian zosterophylls and trimerophytes. Each emergence had a single stoma
Stoma
In botany, a stoma is a pore, found in the leaf and stem epidermis that is used forgas exchange. The pore is bordered by a pair of specialized parenchyma cells known as guard cells that are responsible for regulating the size of the opening...
. The density of the emergences varied so that in regions which had them there were between 3 and 5 or more stomata per mm2. The sporangia did not have emergences, although there were a few stomata.
Kerp et al. suggest that Nothia aphylla was a geophyte which inhabited sandy soils and had a clonal life-style. The underground rhizomes persisted from year to year, continually spreading via lateral branches. The aerial stems appeared annually. They base this analysis on a number features, including evidence that the rhizomes were subterranean, and that rhizomes were still living when erect stems had decayed.
The plant described as Kidstonophyton discoides is possibly the male gametophyte
Gametophyte
A gametophyte is the haploid, multicellular phase of plants and algae that undergo alternation of generations, with each of its cells containing only a single set of chromosomes....
of Nothia aphylla.
Taxonomy
The genus and species were first named by Lyon in 1964. However, Nothia aphylla has been regarded as a nomen nudumNomen nudum
The phrase nomen nudum is a Latin term, meaning "naked name", used in taxonomy...
since no description was published along with the name. Validation of the name has been variously considered to have been by Høeg in 1967, making the botanical authority
Author citation (botany)
In botanical nomenclature, author citation refers to citing the person who validly published a botanical name, i.e. who first published the name while fulfilling the formal requirements as specified by the International Code of Botanical Nomenclature...
"Lyon ex Høeg", or by El-Saadawy and Lacy in 1979, making the authority "Lyon ex El-Saadawy & Lacy".
Nothia has been placed in the group initially established by Banks as the subdivision Zosterophyllophytina or the class Zosterophyllopsida
Zosterophyllopsida
The Zosterophylls are a group of extinct plants. The taxon was first established by Banks in 1968 as the subdivision Zosterophyllophytina; they have since also been treated as the division Zosterophyllophyta and the class Zosterophyllopsida. They were among the first vascular plants in the fossil...
. El-Saadawy and Lacy regard the plant as having affinities with both the rhyniophytes and the zosterophylls. As discussed further below, Kerp et al. regard its taxonomic placement as unclear.
Phylogeny
A cladogram published in 2004 by Crane et al. places Nothia in a paraphyletic stem group of broadly defined "zosterophylls", basal to the lycopsidsLycopodiophyta
The Division Lycopodiophyta is a tracheophyte subdivision of the Kingdom Plantae. It is the oldest extant vascular plant division at around 410 million years old, and includes some of the most "primitive" extant species...
(living and extinct clubmosses and relatives).
A detailed study of Nothia aphylla questions this positioning of the genus, concluding that its taxonomic placement remains unclear, and that the cladistic analyses of Kenrick and Crane (on which the above cladogram is based) have ignored "fundamental differences" between different kinds of emergences (protrusions from stems). Features of the vascular tissue of typical zosterophylls, such as characteristic thickenings of the cells which conduct water, are also absent in Nothia. Earlier, El Saadawy and Lacey had concluded that Nothia was in some ways intermediate between the rhyniophytes and the zosterophylls.
External links
- Cladogram from
