''Huia'' is a

genus Genus ( plural genera ) is a taxonomic rank used in the biological classification of living and fossil organisms as well as viruses. In the hierarchy of biological classification, genus comes above species and below family. In binomial nom ...

of extinct

vascular plant Vascular plants (), also called tracheophytes () or collectively Tracheophyta (), form a large group of land plants ( accepted known species) that have lignified tissues (the xylem) for conducting water and minerals throughout the plant. They ...

s of the

Early Devonian The Early Devonian is the first of three epochs comprising the Devonian period, corresponding to the Lower Devonian series. It lasted from and began with the Lochkovian Stage , which was followed by the Pragian from and then by the Emsian, ...

(Pragian or Siegenian, around ). The genus was first described in 1985 based on fossil specimens from the Posongchong Formation,

Wenshan district Wenshan District is a district in Taipei, Taiwan. It is the southernmost district of the twelve districts in Taipei. ''Wenshan'' previously referred to the region south of the Taipei Basin (including Xindian and Pinglin). History In 1894 (lat ...

, Yunnan, China.

Description

The sporophyte of ''H. recurvata'' consisted of leafless stems (axes), branching both dichotomously and pseudomonopodially (i.e. with unequal divisions creating a 'main stem'). The

sporangia A sporangium (; from Late Latin, ) is an enclosure in which spores are formed. It can be composed of a single cell or can be multicellular. Virtually all plants, fungi, and many other lineages form sporangia at some point in their life cyc ...

(spore-forming organs) were born in terminal spikes on fertile stems, with the sporangia spirally arranged on stalks which curved downwards. The central strand of

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. The ...

contained G-type

tracheid A tracheid is a long and tapered lignified cell in the xylem of vascular plants. It is a type of conductive cell called a tracheary element. Angiosperms use another type of tracheary element, called vessel elements, to transport water through th ...

s. It was initially provisionally assigned to the "

rhyniophyte 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 (around ). Sources vary in the name and rank used for this group, some treating it as the class ...

s". However, this group is defined as having terminal sporangia, whereas those of ''Huia'' are lateral, suggesting affinity with the

zosterophyll 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 Zoste ...

s. A second species, ''H. gracilis'', was described from the Xujiachong Formation (Pragian–early Emsian), Qujing district, Yunnan, China. It differs from ''H. recurvata'' in its more slender morphology and its lack of pseudomonopodial branching. The adaxial sporangia, which were oval or elongated oval in shape, split (dehisced) along their length at right angles to the stem. It is suggested that ''Huia'' may have originated from early ''

Cooksonia ''Cooksonia'' is an extinct group of primitive land plants, treated as a genus, although probably not monophyletic. The earliest ''Cooksonia'' date from the middle of the Silurian (the Wenlock epoch); the group continued to be an important comp ...

''-like plants. Others suggest that its position is uncertain., p. 249

Phylogeny

A cladogram published in 2004 by Crane ''et al.'' places ''Huia'' in a paraphyletic

stem group In phylogenetics, the crown group or crown assemblage is a collection of species composed of the living representatives of the collection, the most recent common ancestor of the collection, and all descendants of the most recent common ancestor. ...

of broadly defined "

s", basal to the lycopsids (living and extinct clubmosses and relatives). By contrast, Hao and Xue in 2013 listed the genus as a

, thus placing it outside the zosterophylls and even lycophytes.

References

External links

Cladogram
from {{Taxonbar, from=Q5934922 Early Devonian plants Prehistoric lycophytes Prehistoric lycophyte genera