''Pellaea atropurpurea'', commonly known as purple-stem cliffbrake or just purple cliffbrake, is a

fern A fern (Polypodiopsida or Polypodiophyta ) is a member of a group of vascular plants (plants with xylem and phloem) that reproduce via spores and have neither seeds nor flowers. The polypodiophytes include all living pteridophytes except t ...

native to North and Central America. ''Brake'' is an old word for fern, related to the word ''

bracken Bracken (''Pteridium'') is a genus of large, coarse ferns in the family Dennstaedtiaceae. Ferns (Pteridophyta) are vascular plants that have alternating generations, large plants that produce spores and small plants that produce sex cells (eggs ...

''. Like many other members of the

Pteridaceae Pteridaceae is a family of ferns in the order Polypodiales, including some 1150 known species in ca 45 genera (depending on taxonomic opinions), divided over five subfamilies. The family includes four groups of genera that are sometimes recogni ...

, it is a rock plant, needing a calcareous substrate. ''P. atropurpurea'' is an apogamous autotriploid, with ''3n=87'' (actual base number, ''n=29''), and is one of the historical parents of the hybrid species complex, '' Pellaea glabella''. Apogamy, or the ability to reproduce non-sexually, is common among rock ferns in the

Characteristics

This fern produces clumps of widely arching

frond A frond is a large, divided leaf. In both common usage and botanical nomenclature, the leaves of ferns are referred to as fronds and some botanists restrict the term to this group. Other botanists allow the term frond to also apply to the lar ...

s. The stipe and

rachis In biology, a rachis (from the grc, ῥάχις [], "backbone, spine") is a main axis or "shaft". In zoology and microbiology In vertebrates, ''rachis'' can refer to the series of articulated vertebrae, which encase the spinal cord. In this c ...

of the blade are purple, while the blade itself has a blue-gray tinge to it. The upper

pinnae The auricle or auricula is the visible part of the ear that is outside the head. It is also called the pinna (Latin for "wing" or " fin", plural pinnae), a term that is used more in zoology. Structure The diagram shows the shape and location ...

are long, narrow, and undivided, while the lower ones are divided into 3–15

pinnule A leaflet (occasionally called foliole) in botany is a leaf-like part of a compound leaf. Though it resembles an entire leaf, a leaflet is not borne on a main plant stem or branch, as a leaf is, but rather on a petiole or a branch of the leaf. Co ...

s. The pinnae are, for the most part, opposite. Fertile fronds are longer and more heavily divided. They produce sori, which lack a true

indusium A sorus (pl. sori) is a cluster of sporangia (structures producing and containing spores) in ferns and fungi. A coenosorus (plural coenosori) is a compound sorus composed of multiple, fused sori. Etymology This New Latin word is from Ancient ...

, within the inrolled margins of the pinnae. This plant may be distinguished from the similar '' Pellaea glabella'' by its hairier nature and larger form.

Ecology

''Pellaea atropurpurea'' grows in the crevices of dry

limestone Limestone ( calcium carbonate ) is a type of carbonate sedimentary rock which is the main source of the material lime. It is composed mostly of the minerals calcite and aragonite, which are different crystal forms of . Limestone forms whe ...

cliffs, rocky slopes, crevices in alvars, and mortared walls. It is endangered in

Florida Florida is a state located in the Southeastern region of the United States. Florida is bordered to the west by the Gulf of Mexico, to the northwest by Alabama, to the north by Georgia, to the east by the Bahamas and Atlantic Ocean, and to ...

Iowa Iowa () is a state in the Midwestern region of the United States, bordered by the Mississippi River to the east and the Missouri River and Big Sioux River to the west. It is bordered by six states: Wisconsin to the northeast, Illinois to the ...

, and

Rhode Island Rhode Island (, like ''road'') is a U.S. state, state in the New England region of the Northeastern United States. It is the List of U.S. states by area, smallest U.S. state by area and the List of states and territories of the United States ...

. It has become extinct in

Louisiana Louisiana , group=pronunciation (French: ''La Louisiane'') is a state in the Deep South and South Central regions of the United States. It is the 20th-smallest by area and the 25th most populous of the 50 U.S. states. Louisiana is borde ...

since the limestone caprock of a

salt dome A salt dome is a type of structural dome formed when salt (or other evaporite minerals) intrudes into overlying rocks in a process known as diapirism. Salt domes can have unique surface and subsurface structures, and they can be discovered using ...

at Winfield, the only location for the fern in the state, was quarried away.

References

Other sources

* * * atropurpurea Ferns of the United States Flora of the Eastern United States {{Pteridaceae-stub