Wenshania
Encyclopedia
Wenshania is a genus of extinct vascular plant
s found in the Posongchong Formation, Yunnan
, China, which is of Early Devonian age (Pragian, around ). 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.
of Wenshania zhichangensis, the type species of the genus, was described from compressed fossils preserved in siltstone. The basal part of the plant is not known, preventing a full reconstruction. The overall height is estimated to be greater than 10 cm, based on the length of the preserved parts. Stems (axes) were smooth and leafless, up to 3.1 mm in diameter, and branched dichotomously or pseudomonopodially (i.e. one branch formed more of a 'main' stem than the other). Specimens show up to three orders of branching. The internal anatomy of the stems is unknown. Spore-forming organs or sporangia
were borne laterally on at least the last two orders of branches, possibly more. Sporangia were flattened, more-or-less circular to kidney-shaped (reniform) in face view, and upright on stalks about 2.5 mm long. They were relatively large, typically up to about 4 mm high and 4 mm wide, although a few were significantly larger. To release its spores, a sporangium split into two 'valves' along a thickened margin at the top. Spores have not been observed.
Associated with stems bearing sporangia were other stems with branches at wide angles, some with short side branches. They are thought to represent a system of basal rhizomes, but direct connections to the aerial stems were not observed. The gametophyte
is unknown.
district of southwestern China. The genus name is derived from the district, the specific epithet from the village. Although similar in some characteristics to the genus Zosterophyllum
Penhallow (1892), that genus was described as having its sporangia in a "loose spike", whereas the specimens concerned have their sporangia distributed over more than one order of branching rather than in a terminal spike. Hence the authors considered that a new genus was required.
group basal to the core zosterophylls can be seen in the summary cladogram shown below.
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 found in the Posongchong Formation, Yunnan
Yunnan
Yunnan is a province of the People's Republic of China, located in the far southwest of the country spanning approximately and with a population of 45.7 million . The capital of the province is Kunming. The province borders Burma, Laos, and Vietnam.Yunnan is situated in a mountainous area, with...
, China, which is of Early Devonian age (Pragian, around ). Plants consisted of leafless stems with simple dichotomous branching, and bore spore-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...
all around the sides of stems. Wenshania is part of the broadly defined group of zosterophylls.
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 Wenshania zhichangensis, the type species of the genus, was described from compressed fossils preserved in siltstone. The basal part of the plant is not known, preventing a full reconstruction. The overall height is estimated to be greater than 10 cm, based on the length of the preserved parts. Stems (axes) were smooth and leafless, up to 3.1 mm in diameter, and branched dichotomously or pseudomonopodially (i.e. one branch formed more of a 'main' stem than the other). Specimens show up to three orders of branching. The internal anatomy of the stems is unknown. Spore-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 laterally on at least the last two orders of branches, possibly more. Sporangia were flattened, more-or-less circular to kidney-shaped (reniform) in face view, and upright on stalks about 2.5 mm long. They were relatively large, typically up to about 4 mm high and 4 mm wide, although a few were significantly larger. To release its spores, a sporangium split into two 'valves' along a thickened margin at the top. Spores have not been observed.
Associated with stems bearing sporangia were other stems with branches at wide angles, some with short side branches. They are thought to represent a system of basal rhizomes, but direct connections to the aerial stems were not observed. The 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....
is unknown.
Taxonomy
The genus Wenshania was created by Zhu and Kenrick in 1998 with a single species, Wenshania zhichangensis. The fossil specimens were found in Zhichang village in the WenshanWenshan Zhuang and Miao Autonomous Prefecture
Wenshan Zhuang and Miao Autonomous Prefecture is an autonomous prefecture in Yunnan Province, China.-Subdivisions:-Ethnic groups:Wenshan is highly diverse...
district of southwestern China. The genus name is derived from the district, the specific epithet from the village. Although similar in some characteristics to the genus Zosterophyllum
Zosterophyllum
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...
Penhallow (1892), that genus was described as having its sporangia in a "loose spike", whereas the specimens concerned have their sporangia distributed over more than one order of branching rather than in a terminal spike. Hence the authors considered that a new genus was required.
Phylogeny
Wenshania is clearly related to the broadly defined group of zosterophylls, as it had flattened, oval to reniform sporangia which were attached to the sides of stems on short stalks and which released spores by splitting into two valves along a thickened border. The genus was described later than the publication of the cladistic studies by Kenrick and Crane which have been the foundation for much of the phylogeny of early land plants. It falls outside the core clade of zosterophylls (Zosterophyllopsida sensu Kenrick & Crane), whose members have sporangia arranged in two rows and new growths with coiled tips. The authors of the genus say that Wenshania most closely resembles Gumuia found in the same stratum, whose current phylogenetic placement in a paraphyleticParaphyly
A group of taxa is said to be paraphyletic if the group consists of all the descendants of a hypothetical closest common ancestor minus one or more monophyletic groups of descendants...
group basal to the core zosterophylls can be seen in the summary cladogram shown below.