Streptanthus polygaloides
Encyclopedia
Streptanthus polygaloides is a species of flowering plant in the mustard family
known by the common name milkwort jewelflower. It is endemic to the Sierra Nevada foothills of California
, where it grows in woodlands and chaparral
, generally on serpentine soil
s.
. In general, it is an annual herb producing a hairless, sometimes waxy-textured stem under 10 centimeters to nearly one meter tall. The ephemeral basal leaves have blades divided into narrow segments and borne on petioles
. Leaves higher on the stem have simple, linear blades up to 10 centimeters long which lack petioles. Flowers occur at intervals along the upper stem. Each has a folded, hooded, calyx of deeply keeled sepal
s in shades of greenish yellow to purple. Brown-veined white petals emerge from the tip. The fruit is a smooth, straight, flat or four-angled silique
up to 5 centimeters in length.
, with hyperaccumulation defined as the presence of at least 1,000 µg
nickel per gram of dry mass. This species averages 2,430 to 18,600 µg/g. This trait helps protect the plant against many types of pathogen
s, including the powdery mildew
Erysiphe polygoni
, the bacterium Xanthomonas campestris
, and the fungus Alternaria brassicola. It also helps defend the plant from leaf-chewing insects such as the red-legged grasshopper (Melanoplus femurrubrum
) and the moth Evergestis rimosalis
, and root-feeding insects like the cabbage maggot (Delia radicum). The high nickel levels in the plant have also been shown to protect it against the diamondback moth (Plutella xylostella
). On the other hand, they do not affect all herbivorous insects that attack the plant, perhaps because some insects eat parts of the plant low in nickel, or can tolerate high-nickel diets, or include other, less toxic plant matter in their diets. In fact, some insects thrive on a high-nickel diet, such as the mirid bug
Melanotrichus boydi, which specializes on this plant.
in soils polluted with heavy metals.
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 name milkwort jewelflower. It is endemic to the Sierra Nevada foothills of California
California
California is a state located on the West Coast of the United States. It is by far the most populous U.S. state, and the third-largest by land area...
, where it grows in woodlands and chaparral
Chaparral
Chaparral is a shrubland or heathland plant community found primarily in the U.S. state of California and in the northern portion of the Baja California peninsula, Mexico...
, generally on serpentine soil
Serpentine soil
A serpentine soil is derived from ultramafic rocks, in particular serpentinite, a rock formed by the hydration and metamorphic transformation of ultramafic rock from the Earth's mantle....
s.
Description
Streptanthus polygaloides is quite variable in morphologyMorphology (biology)
In biology, morphology is a branch of bioscience dealing with the study of the form and structure of organisms and their specific structural features....
. In general, it is an annual herb producing a hairless, sometimes waxy-textured stem under 10 centimeters to nearly one meter tall. The ephemeral basal leaves have blades divided into narrow segments and borne on petioles
Petiole (botany)
In botany, the petiole is the stalk attaching the leaf blade to the stem. The petiole usually has the same internal structure as the stem. Outgrowths appearing on each side of the petiole are called stipules. Leaves lacking a petiole are called sessile, or clasping when they partly surround the...
. Leaves higher on the stem have simple, linear blades up to 10 centimeters long which lack petioles. Flowers occur at intervals along the upper stem. Each has a folded, hooded, calyx of deeply keeled sepal
Sepal
A sepal is a part of the flower of angiosperms . Collectively the sepals form the calyx, which is the outermost whorl of parts that form a flower. Usually green, sepals have the typical function of protecting the petals when the flower is in bud...
s in shades of greenish yellow to purple. Brown-veined white petals emerge from the tip. The fruit is a smooth, straight, flat or four-angled 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...
up to 5 centimeters in length.
Hyperaccumulator of nickel
The Streptanthus polygaloides plant is a hyperaccumulator of nickelNickel
Nickel is a chemical element with the chemical symbol Ni and atomic number 28. It is a silvery-white lustrous metal with a slight golden tinge. Nickel belongs to the transition metals and is hard and ductile...
, with hyperaccumulation defined as the presence of at least 1,000 µg
Microgram
In the metric system, a microgram is a unit of mass equal to one millionth of a gram , or 1/1000 of a milligram. It is one of the smallest units of mass commonly used...
nickel per gram of dry mass. This species averages 2,430 to 18,600 µg/g. This trait helps protect the plant against many types of pathogen
Pathogen
A pathogen gignomai "I give birth to") or infectious agent — colloquially, a germ — is a microbe or microorganism such as a virus, bacterium, prion, or fungus that causes disease in its animal or plant host...
s, including the powdery mildew
Powdery mildew
Powdery mildew is a fungal disease that affects a wide range of plants. Powdery mildew diseases are caused by many different species of fungi in the order Erysiphales. It is one of the easier diseases to spot, as its symptoms are quite distinctive. Infected plants display white powdery spots on the...
Erysiphe polygoni
Erysiphe betae
Erysiphe betae is a plant pathogen. It is a form of powdery mildew that affects sugar beet. The fungus occurs worldwide in all regions where sugar beet is grown and it also infects other edible crops, e.g...
, the bacterium Xanthomonas campestris
Xanthomonas campestris
Xanthomonas campestris is a bacterial species that causes a variety of plant diseases. Available from the NCPPB,and other international Culture collections such as ICMP, ATCC, and LMG in a purified form, it is used in the commercial production of a high-molecular-weight polysaccharide - xanthan...
, and the fungus Alternaria brassicola. It also helps defend the plant from leaf-chewing insects such as the red-legged grasshopper (Melanoplus femurrubrum
Melanoplus femurrubrum
The Red-legged Grasshopper is a species of grasshopper belonging to the genus Melanoplus. It is found in Mexico, United States and Canada.-Description:...
) and the moth Evergestis rimosalis
Evergestis rimosalis
The Cross-striped Cabbageworm is a moth of the Crambidae family. It is found in most of the eastern United States.The wingspan is about 25 mm. The forewings are light brownish-grey with dark grey patches...
, and root-feeding insects like the cabbage maggot (Delia radicum). The high nickel levels in the plant have also been shown to protect it against the diamondback moth (Plutella xylostella
Diamondback moth
The diamondback moth , sometimes called cabbage moth, is a European moth believed to originate in the Mediterranean region that has since spread worldwide. The moth has a short life cycle , is highly fecund and capable of migrating long distances...
). On the other hand, they do not affect all herbivorous insects that attack the plant, perhaps because some insects eat parts of the plant low in nickel, or can tolerate high-nickel diets, or include other, less toxic plant matter in their diets. In fact, some insects thrive on a high-nickel diet, such as the mirid bug
Miridae
The large and diverse insect family Miridae contains the plant bugs, leaf bugs, and grass bugs, and may also be known as capsid bugs. It is the largest family of true bugs belonging to the suborder Heteroptera, with over 10,000 known species and new ones constantly being described...
Melanotrichus boydi, which specializes on this plant.
Phytoremediation
The plant's ability to draw relatively large amounts of nickel from the soil make it of interest as an agent of phytoremediationPhytoremediation
Phytoremediation Phytoremediation Phytoremediation (from the Ancient Greek , and Latin (restoring balance or remediation) describes the treatment of environmental problems (bioremediation) through the use of plants that mitigate the environmental problem without the need to excavate the...
in soils polluted with heavy metals.