Arabis perstellata
Encyclopedia
Arabis perstellata is a rare species of flowering plant in the mustard family
known by the common names Braun's rockcress and Nevada rockcress. It is native to Kentucky
and Tennessee
, where it is known from perhaps 25 total populations. Most of the occurrences have few individuals, and all are deteriorating in quality. The plant grows in shady forest habitat on limestone
substrates, usually near streams or rivers. This is a federally listed endangered species
of the United States.
is a raceme
of flowers with four white or lavender petals each a few millimeters long. The fruit is a hairy silique
1.5 to 2 centimeters in length which contains tiny reddish seeds.
, in the vicinity of the Kentucky River
, and var. ampla (large rockcress), which is known only from Tennessee
. Other authorities do not divide the species and suggest any physical differences are caused by the local environment.
cuts, excessive disturbance is a threat to its existence. Forces such as development, erosion
, and logging
disrupt its habitat. Other threats include competition from non-native plants
, including the invasive
garlic mustard (Alliaria petiolata) and amur honeysuckle
(Lonicera maackii).
Brassicaceae
Brassicaceae, a medium sized and economically important family of flowering plants , are informally known as the mustards, mustard flowers, the crucifers or the cabbage family....
known by the common names Braun's rockcress and Nevada rockcress. It is native to Kentucky
Kentucky
The Commonwealth of Kentucky is a state located in the East Central United States of America. As classified by the United States Census Bureau, Kentucky is a Southern state, more specifically in the East South Central region. Kentucky is one of four U.S. states constituted as a commonwealth...
and Tennessee
Tennessee
Tennessee is a U.S. state located in the Southeastern United States. It has a population of 6,346,105, making it the nation's 17th-largest state by population, and covers , making it the 36th-largest by total land area...
, where it is known from perhaps 25 total populations. Most of the occurrences have few individuals, and all are deteriorating in quality. The plant grows in shady forest habitat on limestone
Limestone
Limestone is a sedimentary rock composed largely of the minerals calcite and aragonite, which are different crystal forms of calcium carbonate . Many limestones are composed from skeletal fragments of marine organisms such as coral or foraminifera....
substrates, usually near streams or rivers. This is a federally listed endangered species
Endangered species
An endangered species is a population of organisms which is at risk of becoming extinct because it is either few in numbers, or threatened by changing environmental or predation parameters...
of the United States.
Characteristics
This rockcress is a perennial herb with decumbent stems reaching 80 centimeters in length. The stems spread out horizontally, and often droop over the side of any structure the plant may be growing on, such as a rock or cliffside. The leaves are arranged in a basal rosette with some alternately arranged along the stem. The stems and leaves are gray-green in color due to a coating of whitish star-shaped hairs. The inflorescenceInflorescence
An inflorescence is a group or cluster of flowers arranged on a stem that is composed of a main branch or a complicated arrangement of branches. Strictly, it is the part of the shoot of seed plants where flowers are formed and which is accordingly modified...
is a raceme
Raceme
A raceme is a type of inflorescence that is unbranched and indeterminate and bears pedicellate flowers — flowers having short floral stalks called pedicels — along the axis. In botany, axis means a shoot, in this case one bearing the flowers. In a raceme, the oldest flowers are borne...
of flowers with four white or lavender petals each a few millimeters long. The fruit is a hairy silique
Silique
A silique or siliqua is a fruit of 2 fused carpels with the length being more than three times the width. The outer walls of the ovary usually separate when ripe, leaving a persistent partition...
1.5 to 2 centimeters in length which contains tiny reddish seeds.
Habitat
Some authorities divide the species into two varieties, var. perstellata (small rockcress), which is mostly limited to Franklin County, KentuckyFranklin County, Kentucky
As of the census of 2000, there were 47,687 people, 19,907 households, and 12,840 families residing in the county. The population density was . There were 21,409 housing units at an average density of...
, in the vicinity of the Kentucky River
Kentucky River
The Kentucky River is a tributary of the Ohio River, long, in the U.S. state of Kentucky. The river and its tributaries drain much of the central region of the state, with its upper course passing through the coal-mining regions of the Cumberland Mountains, and its lower course passing through the...
, and var. ampla (large rockcress), which is known only from Tennessee
Tennessee
Tennessee is a U.S. state located in the Southeastern United States. It has a population of 6,346,105, making it the nation's 17th-largest state by population, and covers , making it the 36th-largest by total land area...
. Other authorities do not divide the species and suggest any physical differences are caused by the local environment.
Endangered status
While the plant is often found in disturbed habitat such as roadRoad
A road is a thoroughfare, route, or way on land between two places, which typically has been paved or otherwise improved to allow travel by some conveyance, including a horse, cart, or motor vehicle. Roads consist of one, or sometimes two, roadways each with one or more lanes and also any...
cuts, excessive disturbance is a threat to its existence. Forces such as development, erosion
Erosion
Erosion is when materials are removed from the surface and changed into something else. It only works by hydraulic actions and transport of solids in the natural environment, and leads to the deposition of these materials elsewhere...
, and logging
Logging
Logging is the cutting, skidding, on-site processing, and loading of trees or logs onto trucks.In forestry, the term logging is sometimes used in a narrow sense concerning the logistics of moving wood from the stump to somewhere outside the forest, usually a sawmill or a lumber yard...
disrupt its habitat. Other threats include competition from non-native plants
Introduced species
An introduced species — or neozoon, alien, exotic, non-indigenous, or non-native species, or simply an introduction, is a species living outside its indigenous or native distributional range, and has arrived in an ecosystem or plant community by human activity, either deliberate or accidental...
, including the invasive
Invasive species
"Invasive species", or invasive exotics, is a nomenclature term and categorization phrase used for flora and fauna, and for specific restoration-preservation processes in native habitats, with several definitions....
garlic mustard (Alliaria petiolata) and amur honeysuckle
Lonicera maackii
Lonicera maackii is a species of honeysuckle in the family Caprifoliaceae, native to temperate Asia in northern and western China , Mongolia, Japan , Korea, and southeastern Russia .It is listed as an endangered species in Japan...
(Lonicera maackii).