''Discalis'' is a

genus Genus (; : genera ) is a taxonomic rank above species and below family (taxonomy), family as used in the biological classification of extant taxon, living and fossil organisms as well as Virus classification#ICTV classification, viruses. In bino ...

of extinct

vascular plant Vascular plants (), also called tracheophytes (, ) or collectively tracheophyta (; ), are plants that have lignin, lignified tissues (the xylem) for conducting water and minerals throughout the plant. They also have a specialized non-lignified Ti ...

s of the

Early Devonian The Early Devonian is the first of three Epoch (geology), epochs comprising the Devonian period, corresponding to the Lower Devonian Series (stratigraphy), series. It lasted from and began with the Lochkovian Stage , which was followed by the Pr ...

(

Pragian The Pragian is one of three faunal stages in the Early Devonian Epoch. It lasted from 410.8 ± 2.8 million years ago to 407.6 ± 2.8 million years ago. It was preceded by the Lochkovian Stage and followed by the Emsian Stage. The most important ...

or Siegenian stage, around ). The name is derived from the Greek , referring to the disc-shaped

sporangia A sporangium (from Late Latin, ; : sporangia) is an enclosure in which spores are formed. It can be composed of a unicellular organism, single cell or can be multicellular organism, multicellular. Virtually all plants, fungus, fungi, and many ot ...

(spore-forming organs). The genus was first described by Hao in 1989 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 ...

, Yunnan, China.

Description

The leafless

sporophyte A sporophyte () is one of the two alternation of generations, alternating multicellular organism, multicellular phases in the biological life cycle, life cycles of plants and algae. It is a diploid multicellular organism which produces asexual Spo ...

of ''D. longistipa'' consisted of creeping stems (axes) up to in diameter with many K- or H-shaped branches as well as upturned or trailing stems, slightly smaller in diameter, which also branched. All stems had irregularly arranged multicellular spines up to long with expanded tips. The stems which did not bear sporangia had coiled (circinnate) tips. Fertile stems bore disc-shaped sporangia laterally on stalks up to 5 mm long, forming open spikes. The sporangia, which were about in diameter, had spines like the stems, and split (dehisced) along their margin to release the trilete

spore In biology, a spore is a unit of sexual reproduction, sexual (in fungi) or asexual reproduction that may be adapted for biological dispersal, dispersal and for survival, often for extended periods of time, in unfavourable conditions. Spores fo ...

s, which were in diameter.

Vascular tissue Vascular tissue is a complex transporting 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. T ...

was present in the stems, with

tracheid A tracheid is a long and tapered Lignin, lignified cell in the xylem of Tracheophyta, vascular plants. It is a type of conductive cell called a tracheary element. Angiosperms also use another type of conductive cell, called vessel elements, to t ...

s having annular, spiral thickenings., p. 254 ''D. longistipa'' somewhat resembles ''

Sawdonia Sawdonia is an extinct genus of early vascular plants, known from the Upper Silurian to the Lower Carboniferous (). ''Sawdonia'' is best recognized by the large number of spikes ( enations) covering the plant. These are vascular plants that do ...

'', but differs in branching pattern and in the arrangement of the sporangia, including their long stalks.

Phylogeny

The evolutionary relationship between spines in early plants and the small leaves (' lycophylls') of later

lycopsid Lycopodiopsida is a class of vascular plants also known as lycopsids, lycopods, or lycophytes. Members of the class are also called clubmosses, firmosses, spikemosses and quillworts. They have dichotomously branching stems bearing simple leaves ...

s (club-mosses and allies) has been much discussed. Hao considered that the spines of ''Discalis'' could be precursors of lycophylls. Boyce regarded the occurrence of the spines of ''Discalis'' on sporangia as evidence that they were not related to lycophylls in this way., p. 491 A cladogram published in 2004 by Crane et al. places ''Discalis'' in a

paraphyletic Paraphyly is a taxonomic term describing a grouping that consists of the grouping's last common ancestor and some but not all of its descendant lineages. The grouping is said to be paraphyletic ''with respect to'' the excluded subgroups. In co ...

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 "

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 Zostero ...

s", basal to the lycopsids (living and extinct clubmosses and relatives). Hao and Xue in 2013 used the absence of terminal

to place the genus in the

order

Gosslingiales Gosslingiales is an Order (biology), order of extinct zosterophylls. The zosterophylls were among the first vascular plants in the fossil record, and share an ancestor with the Lycopodiopsida, living lycophytes. The group has been divided up in ...

, in the family Discaliaceae. The Gosslingiales are considered to be zosterophylls with indeterminate growth and fertile branches generally showing

circinate vernation Vernation or leafing is the formation of new leaves or fronds. In plant anatomy, it is the arrangement of leaves in a bud. In pine species, new leaves are short and encased in sheaths. Each leaf bundle consists of two to five needles. All the l ...

(initially curled up).

References

External links

Cladogram
from {{Taxonbar, from=Q5281411 Early Devonian plants Zosterophylls Prehistoric lycophyte genera