Stylocline citroleum

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Stylocline citroleum

Imperiled (NatureServe)
Scientific classification
Kingdom: Plantae
(unranked): Angiosperms
(unranked): Eudicots
(unranked): Asterids
Order: Asterales
Family: Asteraceae
Tribe: Inuleae
Genus: Stylocline
Species: S. citroleum
Binomial name
Stylocline citroleum

Stylocline citroleum is a rare species of flowering plant in the aster family known by the common name oil neststraw.[1]


It is endemic to Kern County, California, where it is known from about 46 occurrences on and around the Elk Hills Oil Field. The occurrences are patchy and variable in size, and some sources consider them to be part of a single widely spread metapopulation.[2] The species has been collected from coastal San Diego County, but any occurrences there are probably now extirpated.[2][3]

The plant has been known for over one hundred years, and the type specimen was collected in 1935, but it was not described to science as a distinct species until 1992.[4][5]

Stylocline citroleum grows in the valley saltbush scrub ecosystem in the sandy flats and clay soils of the San Joaquin Valley in areas developed into oil fields, the inspiration for the common and scientific names of the species.[4] The plant probably evolved as a hybrid of mountain neststraw (Stylocline gnaphaloides) and California filago (Filago californica), and it is almost always found growing alongside one or both of its parent species.[3]


This inconspicuous annual herb produces a grayish, trailing, forking stem no more than 13 centimeters long. The grayish, woolly, pointed leaves are up to 1.4 centimeters long. The inflorescence bears spherical flower heads just a few millimeters long with tiny, rough-haired phyllaries and scaly, woolly florets. It is hard to tell apart from other Stylocline because its defining characteristics are microscopic.[4]


  1. ^ "Stylocline citroleum". Natural Resources Conservation Service PLANTS Database. USDA. Retrieved 4 December 2015. 
  2. ^ a b The Nature Conservancy
  3. ^ a b Flora of North America
  4. ^ a b c San Joaquin Valley Endangered Species Recovery Program. CSU Stanislaus.
  5. ^ Morefield, J. D. (1992). Three new species of Stylocline (Asteraceae:Inuleae) from California and the Mojave Desert. Madroño 39:114-130.

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