An alvar is a biological environment based on a limestone plain with thin or no soil and, as a result, sparse grassland vegetation. Often flooded in the spring, and affected by drought in midsummer, alvars support a distinctive group of prairie-like plants. Most alvars occur either in northern Europe or around the Great Lakes in North America. This stressed habitat supports a community of rare plants and animals, including species more commonly found on prairie grasslands . Lichen and mosses are common species. Trees and bushes are absent or severely stunted.
15-475: The primary cause of alvars is the shallow exposed bedrock. Flooding and drought, as noted, add to the stress of the site and prevent many species from growing. Disturbance may also play a role. In Europe, grazing is frequent, while in North America, there is some evidence that fire may also prevent encroachment by forest. The habitat also has strong competition gradients, with better competitors occupying
30-587: A representative set of four Ontario alvars, seven habitat types were described. From deep to shallow soil these were: tall grassy meadows, tall forb -rich meadows, low grassy meadows, low forb-rich meadows, dry grassland, rock margin grassland and bare rock flats. Alvars comprise a small percentage of the Earth's ecosystems by land extent. Although some 120 exist in the Great Lakes region, in total there are only about 43 sq mi (110 km) left across
45-607: Is declining elsewhere. Rare plants include Kalm's lobelia ( Lobelia kalmii ) , Pringle's aster ( Symphyotrichum pilosum var. pringlei ) , juniper sedge ( Carex juniperorum ), lakeside daisy ( Hymenoxys acaulis ), ram's-head lady's-slipper ( Cypripedium arietinum ) , and dwarf lake iris ( Iris lacustris ) . Also associated with alvars are rare butterflies and snails . The use of the word "alvar" to refer to this type of environment originated in Sweden . The largest alvar in Europe
60-475: Is located on the Swedish island of Öland . Here the thin soil mantle is only 0.5 to 2.0 centimeters thick in most places and in many extents consists of exposed limestone slabs. The landscape there has been designated a UNESCO World Heritage Site . There are other more local names for similar landforms, such as a pavement barren , although this term is also used for similar landforms based on sandstone . In
75-544: The Pteridophyte Phylogeny Group divided order Polypodiales into six suborders. Pteridaceae is the sole family in suborder Pteridiineae, with 52 genera . The suborder has the same circumscription as Smith et al. used for the family. The phylogenetic relationship between these six suborders is shown in this cladogram : Saccolomatineae Lindsaeineae Pteridiineae Dennstaedtiineae Aspleniineae Polypodiineae The oldest fossil of
90-493: The United Kingdom the exposed landform is called a limestone pavement and thinly covered limestone is known as calcareous grassland . [REDACTED] Media related to Alvar at Wikimedia Commons Pellaea atropurpurea Pellaea atropurpurea , commonly known as purple-stem cliffbrake or just purple cliffbrake , is a fern native to North and Central America. Brake is an old word for fern, related to
105-625: The Vittarioideae subfamily name. The approach was followed by the Pteridophyte Phylogeny Group classification of 2016 (PPG I). Smith et al. (2006) carried out the first higher-level pteridophyte classification published in the molecular phylogenetic era. Smith referred to the ferns as monilophytes, dividing them into four groups. The vast majority of ferns were placed in the Polypodiopsida . In 2016,
120-616: The adiantoid, cheilanthoid, pteridoid, and hemionitidoid ferns. Relationships among these groups remain unclear, and although some recent genetic analyses of the Pteridales suggest that neither the family Pteridaceae nor the major groups within it are all monophyletic , as yet these analyses are insufficiently comprehensive and robust to provide good support for a revision of the order at the family level. Members of Pteridaceae have creeping or erect rhizomes . The leaves are almost always compound and have linear sori that are typically on
135-410: The blade are purple, while the blade itself has a blue-gray tinge to it. The upper pinnae are long, narrow, and undivided, while the lower ones are divided into 3–15 pinnules . The pinnae are, for the most part, opposite. Fertile fronds are longer and more heavily divided. They produce sori , which lack a true indusium , within the inrolled margins of the pinnae. This plant may be distinguished from
150-441: The deeper soil and excluding other species to less productive locations. Crevices in the limestone provide a distinctive habitat which is somewhat protected from grazing, and which may provide habitat for unusual ferns such as Pellaea atropurpurea . Bare rock flats provide areas with extremely low competition that serve as refugia for weak competitors such as the sandwort Minuartia michauxii and Micranthes virginiensis . In
165-543: The entire Great Lakes basin, and many of these have been degraded by agriculture and other human uses. More than half of all remaining alvars occur in Ontario. There are smaller areas in New York, Michigan, Ohio, Wisconsin and Quebec. In North America , alvars provide habitat for birds such as bobolinks , eastern meadowlarks , upland sandpipers , eastern towhees , brown thrashers and loggerhead shrikes whose habitat
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#1732766116794180-522: The limestone caprock of a salt dome at Winfield , the only location for the fern in the state, was quarried away. This Pteridaceae -related article is a stub . You can help Misplaced Pages by expanding it . 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 recognized as separate families:
195-543: The margins of the leaves and lack a true indusium , typically being protected by a false indusium formed from the reflexed margin of the leaf. As traditionally defined, the groups within Pteridaceae are as follows: Based on phylogenetic research, Christenhusz et al. (2011) divided the Pteridaceae genera into five subfamilies. These roughly correspond with the groups listed above, with the main difference being that adiantoid and vittarioid ferns are combined under
210-651: The similar Pellaea glabella by its larger form and by the presence of hairs on the leaf axis (the main leaf stem) and on the underside of the leaflet midribs, which are absent in Pellaea glabella (as reflected in its common name smooth cliffbrake). Pellaea atropurpurea grows in the crevices of dry limestone cliffs, rocky slopes, crevices in alvars, and mortared walls. It is endangered in Florida , Iowa , and Rhode Island . It has become extinct in Louisiana since
225-547: The word bracken . Like many other members of the Pteridaceae , 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 Pteridaceae . This fern produces clumps of widely arching fronds . The stipe and rachis of
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