Pertica
Encyclopedia
Pertica is a genus of extinct vascular plant
s of the Early to Middle Devonian
(around ). It has been placed in the "trimerophytes", a strongly paraphyletic group of early members of the lineage leading to modern ferns and seed plants.
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.
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.
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 of the Early to Middle Devonian
Devonian
The Devonian is a geologic period and system of the Paleozoic Era spanning from the end of the Silurian Period, about 416.0 ± 2.8 Mya , to the beginning of the Carboniferous Period, about 359.2 ± 2.5 Mya...
(around ). It has been placed in the "trimerophytes", a strongly paraphyletic 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 plantPlant
Plants are living organisms belonging to the kingdom Plantae. Precise definitions of the kingdom vary, but as the term is used here, plants include familiar organisms such as trees, flowers, herbs, bushes, grasses, vines, ferns, mosses, and green algae. The group is also called green plants or...
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 paraphyletic stem group basal to the seed plants (spermatophytes) which have such leaves.Other researchers have produced rather different analyses. Rothwell's analysis separates "trimerophytes", like Pertica, from progymnosperms, like Tetraxylopteris
Tetraxylopteris
Tetraxylopteris is a genus of extinct vascular plants of the Middle to Upper Devonian . Fossils were first found in New York State, USA. A second species was later found in Venezuela.-Description:...
, with only the latter being closely related to seed plants.