Demersatheca
Encyclopedia
Demersatheca is a genus of extinct vascular plant
s of the Early Devonian (Pragian, around ). Fossils were first found in the Posongchong Formation of eastern Yunnan, China. The plant had smooth leafless stems at least 1 mm in diameter, but only regions which bore spore
-forming organs or sporangia
are well-known. Sporangia were borne in 'spikes' or strobili, at least 40 mm long; one had 32 sporangia. Sporangia were arranged in four rows, two sporangia being opposite to one another on the stem with the next two being at right angles. Each sporangium consisted of two 'valves' which opened at the top to release their spores. A particular feature of Demersatheca which distinguishes it from other zosterophylls is that the stalk-less sporangia were sunken into the stem of the spike, so that the outer valve was flush with the surface.
contiguum by Li and Cai, based on parts of two spikes (strobili) of sporangia. When further specimens were found, a review by Li and Edwards agreed that the plant was a zosterophyll, but decided that the sunken sporangia and the absence of sporangial stalks were sufficient to require a new genus, Demersatheca. The name is derived from demersus, Latin for sunken, and theca, Latin for container, referring to the organization of the sporangia.
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 (Pragian, around ). Fossils were first found in the Posongchong Formation of eastern Yunnan, China. The plant had smooth leafless stems at least 1 mm in diameter, but only regions which bore 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...
are well-known. Sporangia were borne in 'spikes' or strobili, at least 40 mm long; one had 32 sporangia. Sporangia were arranged in four rows, two sporangia being opposite to one another on the stem with the next two being at right angles. Each sporangium consisted of two 'valves' which opened at the top to release their spores. A particular feature of Demersatheca which distinguishes it from other zosterophylls is that the stalk-less sporangia were sunken into the stem of the spike, so that the outer valve was flush with the surface.
Taxonomy
D. contigua was initially called ZosterophyllumZosterophyllum
Zosterophyllum was a genus of Silurian-Devonian land plant with branching axes.Some species have been transferred to other genera:* Z. artesianum to Danziella artesiana* Z. contiguum to Demersatheca contigua...
contiguum by Li and Cai, based on parts of two spikes (strobili) of sporangia. When further specimens were found, a review by Li and Edwards agreed that the plant was a zosterophyll, but decided that the sunken sporangia and the absence of sporangial stalks were sufficient to require a new genus, Demersatheca. The name is derived from demersus, Latin for sunken, and theca, Latin for container, referring to the organization of the sporangia.