''Streptanthus polygaloides'' is a species of flowering plant in the

mustard family Brassicaceae () or (the older) Cruciferae () is a medium-sized and economically important family of flowering plants commonly known as the mustards, the crucifers, or the cabbage family. Most are herbaceous plants, while some are shrubs. The l ...

known by the common name milkwort jewelflower. It is

endemic Endemism is the state of a species being found in a single defined geographic location, such as an island, state, nation, country or other defined zone; organisms that are indigenous to a place are not endemic to it if they are also found els ...

to the

Sierra Nevada foothills :''See Sierra Nevada for general information about the mountain range in the United States.'' The ecology of the Sierra Nevada, located in the U.S. states of California and Nevada, is diverse and complex: the plants and animals are a significant ...

California California is a state in the Western United States, located along the Pacific Coast. With nearly 39.2million residents across a total area of approximately , it is the most populous U.S. state and the 3rd largest by area. It is also the ...

, where it grows in woodlands and

chaparral Chaparral ( ) is a shrubland plant community and geographical feature found primarily in the U.S. state of California, in southern Oregon, and in the northern portion of the Baja California Peninsula in Mexico. It is shaped by a Mediterrane ...

, generally on serpentine soils.

Description

''Streptanthus polygaloides'' is quite variable in

morphology Morphology, from the Greek and meaning "study of shape", may refer to: Disciplines *Morphology (archaeology), study of the shapes or forms of artifacts *Morphology (astronomy), study of the shape of astronomical objects such as nebulae, galaxies, ...

. 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 A sepal () is a part of the flower of angiosperms (flowering plants). Usually green, sepals typically function as protection for the flower in bud, and often as support for the petals when in bloom., p. 106 The term ''sepalum'' was coined ...

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 A silique or siliqua (plural ''siliques'' or ''siliquae'') is a type of fruit (seed capsule) having two fused carpels with the length being more than three times the width. When the length is less than three times the width of the dried fruit ...

up to 5 centimeters in length.

Hyperaccumulator of nickel

The ''Streptanthus polygaloides'' plant is a

hyperaccumulator A hyperaccumulator is a plant capable of growing in soil or water with very high concentrations of metals, absorbing these metals through their roots, and concentrating extremely high levels of metals in their tissues. The metals are concentrated a ...

nickel Nickel is a chemical element with symbol Ni and atomic number 28. It is a silvery-white lustrous metal with a slight golden tinge. Nickel is a hard and ductile transition metal. Pure nickel is chemically reactive but large pieces are slow ...

, with hyperaccumulation defined as the presence of at least 1,000

µg In the metric system, a microgram or microgramme is a unit of mass equal to one millionth () of a gram. The unit symbol is μg according to the International System of Units (SI); the recommended symbol in the United States and United Kingdom wh ...

nickel per gram of dry mass.Wall, M. A. and R. S. Boyd. (2006). ''Melanotrichus boydi'' (Hemiperta: Miridae) is a specialist on the nickel hyperaccumulator ''Streptanthus polygaloides'' (Brassicaceae). ''The Southwestern Naturalist'' 51:4 481-6. This species averages 2,430 to 18,600 µg/g.Flora of North America
/ref> This trait helps protect the plant against many types of

pathogen In biology, a pathogen ( el, πάθος, "suffering", "passion" and , "producer of") in the oldest and broadest sense, is any organism or agent that can produce disease. A pathogen may also be referred to as an infectious agent, or simply a ger ...

s, including the

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 ascomycete fungi in the order Erysiphales. Powdery mildew is one of the easier plant diseases to identify, as ...

Erysiphe polygoni ''Erysiphe betae'' is a plant pathogen. It is a form of powdery mildew that can affect crops of sugar beet A sugar beet is a plant whose root contains a high concentration of sucrose and which is grown commercially for sugar production. In ...

'', the

bacterium Bacteria (; singular: bacterium) are ubiquitous, mostly free-living organisms often consisting of one biological cell. They constitute a large domain of prokaryotic microorganisms. Typically a few micrometres in length, bacteria were a ...

Xanthomonas campestris ''Xanthomonas campestris'' is a bacterium that causes a variety of plant diseases, including "black rot" in cruciferous vegetables and bacterial wilt of turfgrass. It is also used in the commercial production of xanthan gum, a high-molecula ...

'', and the fungus '' Alternaria brassicola''.Boyd, R. S., et al. (1994). Nickel hyperaccumulation defends ''Streptanthus polygaloides'' (Brassicaceae) against pathogens. ''American Journal of Botany'' 81:3 294-300. 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 one of the most common grasshoppers found in Mexico, the United States, and Canada. This grasshopper is frequently u ...

'') and the moth ''

Evergestis rimosalis ''Evergestis rimosalis'', the cross-striped cabbageworm, is a moth of the family Crambidae. 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. The hind ...

'', and root-feeding insects like the cabbage maggot (''

Delia radicum ''Delia radicum'', known variously as the cabbage fly, cabbage root fly, root fly or turnip fly, is a pest of crops. The larvae of the cabbage root fly are sometimes known as the cabbage maggot or root maggot. The adult flies are about 1 cm ...

'').Jhee, E. M., et al. (2005)
Nickel hyperaccumulation as an elemental defense of ''Streptanthus polygaloides'' (Brassicaceae): Influence of herbivore feeding mode.
''New Phytologist'' 168 331-44. The high nickel levels in the plant have also been shown to protect it against the diamondback moth (''

Plutella xylostella The diamondback moth (''Plutella xylostella''), sometimes called the cabbage moth, is a moth species of the family Plutellidae and genus ''Plutella''. The small, grayish-brown moth sometimes has a cream-colored band that forms a diamond along i ...

'').Jhee, E. M., et al. (2006). Nickel hyperaccumulation by ''Streptanthus polygaloides'' protects against the folivore ''Plutella xylostella'' (Lepidoptera: Plutellidae). ''Plant Ecology'' 183:1 91-104. 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.Martens, S. M. and R. S. Boyd. (2002)
The defensive role of Ni hyperaccumulation by plants: a field experiment.
''American Journal of Botany'' 89 998-1003. In fact, some insects thrive on a high-nickel diet, such as the mirid bug '' 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

phytoremediation Phytoremediation technologies use living plants to clean up soil, air and water contaminated with hazardous contaminants. It is defined as "the use of green plants and the associated microorganisms, along with proper soil amendments and agronomi ...

in soils polluted with heavy metals.Boyd, R. S. and M. A. Davis. (2001). Metal tolerance and accumulation ability of the Ni hyperaccumulator ''Streptanthus polygaloides'' Gray (Brassicaceae). ''International Journal of Phytoremediation'' 3:4 353-67.

References

External links

Jepson Manual Treatment - ''Streptanthus polygaloides''''Streptanthus polygaloides'' - Photo gallery
{{Taxonbar, from=Q7623328

polygaloides ''Polygaloides'' is a genus of flowering plants belonging to the family Polygalaceae. Species , ''Plants of the World Online'' accepted the following species: *'' Polygaloides balansae'' (Coss.) O.Schwarz *'' Polygaloides chamaebuxus'' (L.) O. ...

Endemic flora of California Flora of the Sierra Nevada (United States) Flora without expected TNC conservation status