Ventarura
Encyclopedia
Ventarura is a genus of extinct vascular plant
s of the Early Devonian (around ). 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.
, both located near the village of Rhynie, Scotland. Only fragmentary fossils were found, the longest being around 12 cm long. Stems (axes) of two kinds were found, although without clear connections between them. Aerial stems were leafless, smooth and dichotomously branched. They contained an exarch
xylem
strand containing G-type tracheid
s. Alone among the Rhynie chert plants, there was evidence of sclerenchyma – supporting tissue made up of dead cells with thick cell walls. Spore
-forming organs or sporangia
were borne on the sides of the stems, attached without clear stalks. They consisted of two circular to pear-shaped 'valves', one slightly narrower facing the stem, one away from it. Sporangia may have formed a two-rowed spike or strobilus. Spores were shed via a slit at the top of the sporangium between thickened valve borders. Spores were of one kind, about 67 µm in diameter, without trilete marks.
What are thought to be the underground stems of Ventarura had single-celled hairs, presumably rhizoids, on all sides. They branched irregularly and more often compared to aerial stems.
studies published by Kenrick and Crane in 1997 which are the source of much of the information on the phylogeny of early land plants (see Polysporangiophytes: Taxonomy). The shape of the sporangia and their lateral position as well as the anatomy of the xylem show a clear relationship to the zosterophylls. However, the arrangement of the sporangia is difficult to determine from the fossil specimens. Zosterophylls are thought to be the earliest diverging group of lycophytes, a group which includes modern clubmosses and relatives.
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 of the Early Devonian (around ). Fossils were found in the Windyfield 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...
, Rhynie, Scotland. Some features, such as bivalved sporangia borne laterally and the anatomy of the xylem
Xylem
Xylem is one of the two types of transport tissue in vascular plants. . The word xylem is derived from the Classical Greek word ξυλον , meaning "wood"; the best-known xylem tissue is wood, though it is found throughout the plant...
, relate this genus to the zosterophylls. Other features are unclear due to poor preservation.
Description
Fossils of Ventarura were found in the Windyfield chert, slightly separate from the better-known Rhynie chertRhynie 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...
, both located near the village of Rhynie, Scotland. Only fragmentary fossils were found, the longest being around 12 cm long. Stems (axes) of two kinds were found, although without clear connections between them. Aerial stems were leafless, smooth and dichotomously branched. They contained an exarch
Exarch
In the Byzantine Empire, an exarch was governor with extended authority of a province at some remove from the capital Constantinople. The prevailing situation frequently involved him in military operations....
xylem
Xylem
Xylem is one of the two types of transport tissue in vascular plants. . The word xylem is derived from the Classical Greek word ξυλον , meaning "wood"; the best-known xylem tissue is wood, though it is found throughout the plant...
strand containing G-type tracheid
Tracheid
Tracheids are elongated cells in the xylem of vascular plants that serve in the transport of water and mineral salts. Tracheids are one of two types of tracheary elements, vessel elements being the other. All tracheary elements develop a thick lignified cell wall, and at maturity the protoplast...
s. Alone among the Rhynie chert plants, there was evidence of sclerenchyma – supporting tissue made up of dead cells with thick cell walls. Spore
Spore
In biology, a spore is a reproductive structure that is adapted for dispersal and surviving for extended periods of time in unfavorable conditions. Spores form part of the life cycles of many bacteria, plants, algae, fungi and some protozoa. According to scientist Dr...
-forming organs or 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...
were borne on the sides of the stems, attached without clear stalks. They consisted of two circular to pear-shaped 'valves', one slightly narrower facing the stem, one away from it. Sporangia may have formed a two-rowed spike or strobilus. Spores were shed via a slit at the top of the sporangium between thickened valve borders. Spores were of one kind, about 67 µm in diameter, without trilete marks.
What are thought to be the underground stems of Ventarura had single-celled hairs, presumably rhizoids, on all sides. They branched irregularly and more often compared to aerial stems.
Phylogeny
Ventarura was described too late to be included in the cladisticCladistics
Cladistics is a method of classifying species of organisms into groups called clades, which consist of an ancestor organism and all its descendants . For example, birds, dinosaurs, crocodiles, and all descendants of their most recent common ancestor form a clade...
studies published by Kenrick and Crane in 1997 which are the source of much of the information on the phylogeny of early land plants (see Polysporangiophytes: Taxonomy). The shape of the sporangia and their lateral position as well as the anatomy of the xylem show a clear relationship to the zosterophylls. However, the arrangement of the sporangia is difficult to determine from the fossil specimens. Zosterophylls are thought to be the earliest diverging group of lycophytes, a group which includes modern clubmosses and relatives.