''Layia discoidea'' is a rare species of flowering plant in the family

Asteraceae The family Asteraceae, alternatively Compositae, consists of over 32,000 known species of flowering plants in over 1,900 genera within the order Asterales. Commonly referred to as the aster, daisy, composite, or sunflower family, Compositae w ...

known by the common name rayless tidytips, or rayless layia.

Distribution

''Layia discoidea'' is a local serpentine endemic where it is known only from the

Diablo Range The Diablo Range is a mountain range in the California Coast Ranges subdivision of the Pacific Coast Ranges in northern California, United States. It stretches from the eastern San Francisco Bay area at its northern end to the Salinas Valley are ...

in southern

San Benito County San Benito County (; ''San Benito'', Spanish for "St. Benedict"), officially the County of San Benito, is a county located in the Coast Range Mountains of the U.S. state of California. As of the 2020 census, the population was 64,209. The coun ...

and far western

Fresno County Fresno County (), officially the County of Fresno, is a county located in the central portion of the U.S. state of California. As of the 2020 Census, the population was 1,008,654. The county seat is Fresno, the fifth-most populous city in Cali ...

. The known distribution of the species is the

New Idria New Idria was an Unincorporated area, unincorporated town in San Benito County, California. It was named after the New Idria Mercury Mine, which closed in 1972, resulting in a ghost town. Geography The area is inside Area code 831. It is included ...

serpentine mass (BLM Clear Creek Management Area) and nearby Laguna Mountain, Hepsedam Peak, and Panther Peak serpentine masses. ''Layia discoidea'' is regarded as a strict serpentine

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 elsew ...

with several populations known (as of 2017) to occur on greywacke and chert outcrop and talus at the edge of the New Idria Serpentine Mass near Condon Peak, Sampson Peak, and Idria Reservoir. Typical habitat of the species is serpentine rock outcrop, serpentine talus, and serpentine stream terraces where it grows in full sun with little to no competition from other plant species. The shale and chert outcrop habitat that a few populations of ''Layia discoidea'' grows on has similar (analogous) physical and microclimate conditions as the serpentine habitat that the species is primarily found growing.

Description

This is an annual herb growing a small glandular stem to a maximum height of about 20 centimeters. The thin leaves are generally lance-shaped, but the larger leaves on the lower part of the stem are usually lobed. Unlike other ''Layia'' species, which are known for their prominent white or yellow ray florets, ''Layia discoidea'' has no ray florets or real

phyllaries In botanical terminology, a phyllary, also known an involucral bract or tegule, is a single bract of the involucre of a composite flower. The involucre is the grouping of bracts together. Phyllaries are reduced leaf-like structures that form one or ...

. The

flower head A pseudanthium (Greek for "false flower"; ) is an inflorescence that resembles a flower. The word is sometimes used for other structures that are neither a true flower nor a true inflorescence. Examples of pseudanthia include flower heads, compos ...

is a cluster of many deep yellow disc florets with a base of bractlike scales. The fruit is an

achene An achene (; ), also sometimes called akene and occasionally achenium or achenocarp, is a type of simple dry fruit produced by many species of flowering plants. Achenes are monocarpellate (formed from one carpel) and indehiscent (they do not ope ...

with a short scaly brown pappus.

Speciation

Genetic analysis performed on this species suggest that it evolved directly from '' Layia glandulosa'' in what may be an example of both

allopatric speciation Allopatric speciation () – also referred to as geographic speciation, vicariant speciation, or its earlier name the dumbbell model – is a mode of speciation that occurs when biological populations become geographically isolated from ...

and

peripatric speciation Peripatric speciation is a mode of speciation in which a new species is formed from an isolated peripheral population. Since peripatric speciation resembles allopatric speciation, in that populations are isolated and prevented from exchanging g ...

. ''Layia discoidea'' looks quite different from the white-rayed ''Layia glandulosa'', and it lives in a specialized habitat, but the two species are genetically very similar and produce robust, fertile hybrids when crossed. Known extant ''Layia glandulosa'' populations within the range of ''Layia discoidea'' typically have deep yellow ray florets. Individuals of ''Layia discoidea'' occasionally display ray florets that are light yellow in color (see Calphotos and Harrison 2013). Individuals bearing ray florets have been observed in populations at the New Idria, Laguna Mountain, and Panther Peak serpentine masses. It is unclear if the ray florets are a result of hybridization with nearby ''Layia glandulosa'', a genetic mutation, or simply induced by environmental conditions.

References

Harrison SP. 2013. Plant and Animal Endemism in California. University of California Press.

External links

Jepson Manual TreatmentUSDA Plants ProfilePhoto gallery
{{Taxonbar, from=Q6505563 discoidea Endemic flora of California ~ Natural history of the California chaparral and woodlands Natural history of San Benito County, California Natural history of Fresno County, California