''Pertica'' 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 to Middle

Devonian The Devonian ( ) is a geologic period and system of the Paleozoic era, spanning 60.3 million years from the end of the Silurian, million years ago (Mya), to the beginning of the Carboniferous, Mya. It is named after Devon, England, wh ...

(around ). It has been placed in the " trimerophytes", a strongly

paraphyletic In taxonomy, a group is paraphyletic if it consists of the group's last common ancestor and most of its descendants, excluding a few monophyletic subgroups. The group is said to be paraphyletic ''with respect to'' the excluded subgroups. In ...

group of early members of the lineage leading to modern ferns and seed plants.

Description

''Pertica quadrifaria'' (the type species of the genus) was described in 1972 from compression fossils found in the Trout Valley Formation of northern Maine, USA. It was an upright

plant Plants are predominantly photosynthetic eukaryotes of the kingdom Plantae. Historically, the plant kingdom encompassed all living things that were not animals, and included algae and fungi; however, all current definitions of Plantae excl ...

which grew to perhaps as much as a metre (3 ft) in height. It comprised a main, straight stem (axis) with side branches which developed dichotomously, branching many times at increasingly shorter intervals. Some of the terminal branchlets bore masses of erect paired, ellipsoidal sporangia in distinctive tight clusters. The branches were arranged in a spiral pattern, forming four vertical rows. The specific epithet ''quadrifaria'' refers to this growth habit. ''Pertica varia'' was described in 1976 from the Devonian of Eastern Canada. It was considerably taller than ''P. quadrifaria'', reaching a height of nearly 3 m. The sporangia were similar to those of ''P. quadrifaria'', although there were fewer in each cluster. ''Pertica dalhousii'' was described in 1978 from fossils of Early or Middle Devonian age found in New Brunswick, Canada. The plant appears to have been similar to ''P. quadrifaria'' (only part is known), comprising a central stem (axis) with spirally arranged dichotomous side branches, some of which terminated in erect clusters of between 32 and 128 sporangia. Further specimens from the same rocks possibly belonged to another species of ''Pertica'', but were not sufficiently well preserved to be named.

Phylogeny

The clear differentiation between a main stem (axis) and lateral branches in ''Pertica'', as in other "trimerophytes", has been considered to represent an early stage in the development of a growth pattern that later led to the evolution of megaphylls (large true leaves). Consistent with this, a cladogram published in 2004 by Crane et al. places ''Pertica'' in a

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. ...

basal to the

seed plant A spermatophyte (; ), also known as phanerogam (taxon Phanerogamae) or phaenogam (taxon Phaenogamae), is any plant that produces seeds, hence the alternative name seed plant. Spermatophytes are a subset of the embryophytes or land plants. They inc ...

s (spermatophytes) which have such leaves. Other researchers have produced rather different analyses. Rothwell's analysis separates "trimerophytes", like ''Pertica'', from progymnosperms, like ''

Tetraxylopteris '' Tetraxylopteris'' is a genus of extinct vascular plants of the Middle to Upper Devonian (around ). Fossils were first found in New York State, USA. A second species was later found in Venezuela. Description Fossils of ''Tetraxylopteris'' ha ...

'', with only the latter being closely related to seed plants.

References

{{Taxonbar, from=Q3900572 Early Devonian plants Middle Devonian plants Early Devonian first appearances Middle Devonian genus extinctions Paleozoic life of New Brunswick Prehistoric plant genera