''Pertica'' 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 to Middle

Devonian The Devonian ( ) is a period (geology), geologic period and system (stratigraphy), system of the Paleozoic era (geology), era during the Phanerozoic eon (geology), eon, spanning 60.3 million years from the end of the preceding Silurian per ...

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

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 ...

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

Description

''Pertica quadrifaria'' (the

type Type may refer to: Science and technology Computing * Typing, producing text via a keyboard, typewriter, etc. * Data type, collection of values used for computations. * File type * TYPE (DOS command), a command to display contents of a file. * ...

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 the eukaryotes that form the Kingdom (biology), kingdom Plantae; they are predominantly Photosynthesis, photosynthetic. This means that they obtain their energy from sunlight, using chloroplasts derived from endosymbiosis with c ...

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 basal to the

seed plant A seed plant or spermatophyte (; New Latin ''spermat-'' and Greek ' (phytón), plant), also known as a phanerogam (taxon Phanerogamae) or a phaenogam (taxon Phaenogamae), is any plant that produces seeds. It is a category of embryophyte (i.e. la ...

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