Nothia aphylla Temporal range: | |
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Scientific classification ![]() | |
Kingdom: | Plantae |
Clade: | Tracheophytes |
Clade: | Lycophytes |
Plesion: | † Zosterophylls (?) |
Genus: | † Nothia A.G.Lyon ex El-Saadawy & Lacy [1] |
Species: | †N. aphylla |
Binomial name | |
†Nothia aphylla Lyon ex El-Saadawy & Lacy [1] | |
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. [1]
Fossilized remains, including bare stems (axes) and detached spore-forming organs (sporangia), were first described by Kidston and Lang in 1920 from the Rhynie chert of Aberdeenshire, Scotland – rocks which are of Pragian age ( 411 to 408 million years ago). 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. [2] The first full description based on further specimens was published in 1979. [3] A very detailed description was published in 2001, making this species one of the best-known early polysporangiophytes. [1]
The sporophyte 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 rhizoids 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. [4] 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. [1] [3]
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. [1]
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. [5]
The plant described as Kidstonophyton discoides is possibly the male gametophyte of Nothia aphylla. [6]
The genus and species were first named by Lyon in 1964. [2] However, Nothia aphylla has been regarded as a nomen nudum 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", [3] or by El-Saadawy and Lacy in 1979, making the authority "Lyon ex El-Saadawy & Lacy". [1]
Nothia has been placed in the group initially established by Banks as the subdivision Zosterophyllophytina or the class Zosterophyllopsida (zosterophylls). El-Saadawy and Lacy regard the plant as having affinities with both the rhyniophytes and the zosterophylls. [3] As discussed further below, Kerp et al. regard its taxonomic placement as unclear.
A cladogram published in 2004 by Crane et al. places Nothia in a paraphyletic stem group of broadly defined "zosterophylls", basal to the lycopsids (living and extinct clubmosses and relatives). [7]
lycophytes |
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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. [8] Earlier, El Saadawy and Lacey had concluded that Nothia was in some ways intermediate between the rhyniophytes and the zosterophylls. [3] Hao and Xue in 2013 listed the genus as a zosterophyll. [9]
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.
Psilotum is a genus of fern-like vascular plants. It is one of two genera in the family Psilotaceae commonly known as whisk ferns, the other being Tmesipteris. Plants in these two genera were once thought to be descended from the earliest surviving vascular plants, but more recent phylogenies place them as basal ferns, as a sister group to Ophioglossales. They lack true roots and leaves are very reduced, the stems being the organs containing photosynthetic and conducting tissue. There are only two species in Psilotum and a hybrid between the two. They differ from those in Tmesipteris in having stems with many branches and a synangium with three lobes rather than two.
The Rhynie chert is a Lower 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. The Rhynie chert contains exceptionally preserved plant, fungus, lichen and animal material preserved in place by an overlying volcanic deposit. The bulk of the Devonian fossil bed consists of primitive plants, along with arthropods, lichens, algae and fungi.
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.
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.
Drepanophycales is an order of extinct lycophyte plants of Late Silurian to Late Devonian age, found in North America, China, Russia, Europe, and Australia. Sometimes known as the Asteroxylales or Baragwanathiales.
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.
Polysporangiophytes, also called polysporangiates or formally Polysporangiophyta, are plants in which the spore-bearing generation (sporophyte) has branching stems (axes) that bear sporangia. The name literally means 'many sporangia plant'. The clade includes all land plants (embryophytes) except for the bryophytes whose sporophytes are normally unbranched, even if a few exceptional cases occur. While the definition is independent of the presence of vascular tissue, all living polysporangiophytes also have vascular tissue, i.e., are vascular plants or tracheophytes. Extinct polysporangiophytes are known that have no vascular tissue and so are not tracheophytes.
Aglaophyton major was the sporophyte generation of a diplohaplontic, pre-vascular, axial, free-sporing land plant of the Lower Devonian. It had anatomical features intermediate between those of the bryophytes and vascular plants or tracheophytes.
Rhynia is a single-species genus of Devonian vascular plants. Rhynia gwynne-vaughanii was the sporophyte generation of a vascular, axial, free-sporing diplohaplontic embryophytic land plant of the Early Devonian that had anatomical features more advanced than those of the bryophytes. Rhynia gwynne-vaughanii was a member of a sister group to all other eutracheophytes, including modern vascular plants.
Horneophyton is an extinct early plant which may form a "missing link" between the hornworts and the Rhyniopsida. It is a member of the class Horneophytopsida. Horneophyton is among the most abundant fossil organisms found in the Rhynie chert, a Devonian Lagerstätte in Aberdeenshire, UK. A single species, Horneophyton lignieri, is known. Its probable female gametophyte is the form taxon Langiophyton mackiei.
Psilophytopsida is a now obsolete class containing one order, Psilophytales, which was previously used to classify a number of extinct plants which are now placed elsewhere. The class was established in 1917, under the name Psilophyta, with only three genera for a group of fossil plants from the Upper Silurian and Devonian periods which lack true roots and leaves, but have a vascular system within a branching cylindrical stem. The living Psilotaceae, the whisk-ferns, were sometimes added to the class, which was then usually called Psilopsida. This classification is no longer in use.
Hicklingia is a genus of extinct plants of the Middle Devonian. Compressed specimens were first described in 1923 from the Old Red Sandstone of Scotland. Initially the genus was placed in the "rhyniophytes", but this group is defined as having terminal sporangia, and later work showed that the sporangia of Hicklingia were lateral rather than strictly terminal, so that it is now regarded as having affinities with the zosterophylls.
Huia is a genus of extinct vascular plants of the Early Devonian. The genus was first described in 1985 based on fossil specimens from the Posongchong Formation, Wenshan district, Yunnan, China.
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.
Dutoitia is a genus of Devonian rhyniophyte, named after the renowned South African geologist Alex du Toit. It is one of the earliest plants from Gondwana to colonize land. Its fossils were preserved in fine mudstones of the 400-million-year-old Bokkeveld and Witteberg Groups of South Africa. This erect, gracile plant is less than 10 cm high and very simple in structure. Its diminutive stems, which are devoid of leaflike appendages, branch in two and end in club- or cup-shaped sporangia, occasionally containing its reproductive spores. Stomata are present in the cuticle of their stems for gas exchange, and primitive cells inside the stems transported water from the roots to the aerial parts of the plant. Three species are recognized, D. pulchra Hoeg 1930, D. alfreda Plumstead 1967 and D. maraisia Plumstead 1967.
Ventarura is a genus of extinct vascular plants of the Early Devonian. Fossils were found in the Windyfield chert, Rhynie, Scotland. Some features, such as bivalved sporangia borne laterally and the anatomy of the xylem, relate this genus to the zosterophylls. Other features are unclear due to poor preservation.
Trichopherophyton is a genus of extinct vascular plants of the Early Devonian. Fossils were found in the Rhynie chert, Scotland. The remains are very fragmentary, but the plant appears to be related to the zosterophylls.
Wenshania is a genus of extinct vascular plants found in the Posongchong Formation, Yunnan, China, which is of Early Devonian age. Plants consisted of leafless stems with simple dichotomous branching, and bore spore-forming organs or sporangia all around the sides of stems. Wenshania is part of the broadly defined group of zosterophylls.
Macivera is a genus of extinct vascular plants. Fossils were found in sediments in Bathust Island, Nunavut, Canada, from the upper Silurian. The leafless stems (axes) branched dichotomously and were relatively thin, being between 0.7 and 1.0 mm wide. Spore-forming organs or sporangia, which were elliptical, being longer than wide, were borne on the end regions of stems. Macivera is considered to be a zosterophyll.