''Senecio eboracensis'', the York groundsel or York radiate groundsel, is a

flowering plant Flowering plants are plants that bear flowers and fruits, and form the clade Angiospermae (). The term angiosperm is derived from the Ancient Greek, Greek words (; 'container, vessel') and (; 'seed'), meaning that the seeds are enclosed with ...

in the daisy family

Asteraceae Asteraceae () is a large family (biology), family of flowering plants that consists of over 32,000 known species in over 1,900 genera within the Order (biology), order Asterales. The number of species in Asteraceae is rivaled only by the Orchi ...

. It is a hybrid between a native and a non-native introduced species, which naturalised in England but the population failed to sustain itself. It was brought back by captive cultivation. It is a self-pollinating

hybrid Hybrid may refer to: Science * Hybrid (biology), an offspring resulting from cross-breeding ** Hybrid grape, grape varieties produced by cross-breeding two ''Vitis'' species ** Hybridity, the property of a hybrid plant which is a union of two diff ...

species A species () is often defined as the largest group of organisms in which any two individuals of the appropriate sexes or mating types can produce fertile offspring, typically by sexual reproduction. It is the basic unit of Taxonomy (biology), ...

of ragwort and one of only six new plant species to be discovered in either the

United Kingdom The United Kingdom of Great Britain and Northern Ireland, commonly known as the United Kingdom (UK) or Britain, is a country in Northwestern Europe, off the coast of European mainland, the continental mainland. It comprises England, Scotlan ...

North America North America is a continent in the Northern Hemisphere, Northern and Western Hemisphere, Western hemispheres. North America is bordered to the north by the Arctic Ocean, to the east by the Atlantic Ocean, to the southeast by South Ameri ...

in the last 100 years. The plant was first discovered in

York York is a cathedral city in North Yorkshire, England, with Roman Britain, Roman origins, sited at the confluence of the rivers River Ouse, Yorkshire, Ouse and River Foss, Foss. It has many historic buildings and other structures, such as a Yor ...

England England is a Countries of the United Kingdom, country that is part of the United Kingdom. It is located on the island of Great Britain, of which it covers about 62%, and List of islands of England, more than 100 smaller adjacent islands. It ...

in 1979 and last seen in the wild in 1991. A survey by UK government advisory body Natural England found it was driven to extinction by 2000, partly due to the use of weedkiller. Seeds of the plant were stored at the Millennium Seed Bank, successfully germinated, and reintroduced to York in 2023.

Description

York radiate groundsel is an annual

herbaceous plant Herbaceous plants are vascular plants that have no persistent woody stems above ground. This broad category of plants includes many perennials, and nearly all annuals and biennials. Definitions of "herb" and "herbaceous" The fourth edition o ...

that sets its seed within the 3 months that it takes this plant to mature from germination to the upwards of high adult plant. With yellow daisy-like flowers from its Sicilian parent ('' S. squalidus'') but also with the less-promiscuous habits of its native parent ('' S. vulgaris''), this member of the genus ''

Senecio ''Senecio'' is a genus of flowering plants in the daisy family (Asteraceae) that includes ragworts and groundsels. Variously circumscribed taxonomically, the genus ''Senecio'' is one of the largest genera of flowering plants. Description Mo ...

'' is morphologically distinct from related species. Senecio eboracensis leaf linedrawing

:Leaves and stems ''S. eboracensis'' have large many lobed leaves divided into slender segments, the clefts not reaching the midrib. The

stem Stem or STEM most commonly refers to: * Plant stem, a structural axis of a vascular plant * Stem group * Science, technology, engineering, and mathematics Stem or STEM can also refer to: Language and writing * Word stem, part of a word respon ...

s are mostly erect to ascending with an occasional horizontal base section up to with '

adventitious Important structures in plant development are buds, shoots, roots, leaves, and flowers; plants produce these tissues and structures throughout their life from meristems located at the tips of organs, or between mature tissues. Thus, a living plant ...

roots' at base. The upper and lower leaves petiolate and lobes appearing at quarter whole leaf lengths along the midrib. The upper leaves are generally more deeply lobed and in lobed pairs. Leaves on plants grown in fertile soils or in greenhouses can be much more luxurious and more highly dissected (or more finely divided into slender segments) up to x with lobes appearing at fifth whole leaf lengths along the midrib. Leaf edges throughout are dentate or sometimes divided into lobes. :Flowers York groundsel has flower-heads that are more showy than those of its parent groundsel. The flower-head, found at the tips of the plants ( apical) appearing in clusters (an

inflorescence In botany, an inflorescence is a group or cluster of flowers arranged on a plant's Plant stem, stem that is composed of a main branch or a system of branches. An inflorescence is categorized on the basis of the arrangement of flowers on a mai ...

) usually consist of three to seven

floret This glossary of botanical terms is a list of definitions of terms and concepts relevant to botany and plants in general. Terms of plant morphology are included here as well as at the more specific Glossary of plant morphology and Glossary ...

s grouped in a

corymb Corymb is a botanical term for an inflorescence with the flowers growing in such a fashion that the outermost are borne on longer pedicels than the inner, bringing all flowers up to a common level. A corymb has a flattish top with a superficial re ...

; at first dense and leafy but eventually less dense with peduncles 5 to 20 millimeters (0.2 to 0.8 in) which get longer when fruiting (up to 25 mm (1 in)). The flower-head is broadly cylindrical 10×4 millimeters (0.4×0.16 in), becoming slightly bell shaped) when the bright

yellow Yellow is the color between green and orange on the spectrum of light. It is evoked by light with a dominant wavelength of roughly 575585 nm. It is a primary color in subtractive color systems, used in painting or color printing. In t ...

ray florets Asteraceae () is a large family of flowering plants that consists of over 32,000 known species in over 1,900 genera within the order Asterales. The number of species in Asteraceae is rivaled only by the Orchidaceae, and which is the larger fa ...

open. Involucral

bracts In botany, a bract is a modified or specialized leaf, associated with a reproductive structure such as a flower, inflorescence axis or cone scale. Bracts are usually different from foliage leaves in size, color, shape or texture. They also loo ...

sparse (4-8), elongated (3.5–4 mm), usually without black tips. The

ligules A ligule (from "strap", variant of ''lingula'', from ''lingua'' "tongue") is a thin outgrowth at the junction of leaf and leafstalk of many Poaceae, grasses (family Poaceae) and Cyperaceae, sedges (family Cyperaceae). A ligule is also a strap-shap ...

are narrow, 5 to 7 millimeters (0.2 to 0.24 in) long and 1.5 millimeters (0.06 in) wide), occasionally becoming revolute. :Seeds The

achene An achene (; ), also sometimes called akene and occasionally achenium or achenocarp, is a type of simple fruit, simple dry fruits, dry fruit produced by many species of flowering plants. Achenes are monocarpellate (formed from one carpel) and Dehi ...

s can be 2.5 to 3.5 millimeters (0.1 to 0.15 in) long, are straight and shallowly grooved. The smooth ribs are hairless while the grooves are covered with hairs. The silky white, umbrella-like pappus readily detaches from the fruit when ripe.

Name

The word

Eboracum Eboracum () was a castra, fort and later a coloniae, city in the Roman province of Roman Britain, Britannia. In its prime it was the largest town in northern Britain and a provincial capital. The site remained occupied after the decline of the ...

, the classical name of

, was chosen in the year 2000 to describe this

tetraploid Polyploidy is a condition in which the cells of an organism have more than two paired sets of ( homologous) chromosomes. Most species whose cells have nuclei (eukaryotes) are diploid, meaning they have two complete sets of chromosomes, one fro ...

hybrid derivative informally named 'York radiate groundsel' at the time a formal description was made.

Distribution

York groundsel occurs on disturbed ground, car park perimeters, pavement cracks and other urban/industrial sites; specifically in disturbed areas near to the railways in

. One of the parents ''

Senecio vulgaris ''Senecio vulgaris'', often known by the common names groundsel and old-man-in-the-spring, is a flowering plant in the family Asteraceae. It is an annual plant, annual herbaceous plant, herb, native to the Palaearctic and widely naturalised as a ...

'' is a native to the area while the other parent ''

Senecio squalidus ''Senecio squalidus'', known as Oxford ragwort, is a flowering plant in the daisy family Asteraceae. It is a yellow-flowered herbaceous plant, native to mountainous, rocky or volcanic areas, that has managed to find other homes on man-made and n ...

'' was introduced from

Mount Etna Mount Etna, or simply Etna ( or ; , or ; ; or ), is an active stratovolcano on the east coast of Sicily, Italy, in the Metropolitan City of Catania, between the cities of Messina, Italy, Messina and Catania. It is located above the Conve ...

Sicily Sicily (Italian language, Italian and ), officially the Sicilian Region (), is an island in the central Mediterranean Sea, south of the Italian Peninsula in continental Europe and is one of the 20 regions of Italy, regions of Italy. With 4. ...

in 1690 to the

Oxford Botanic Garden The University of Oxford Botanic Garden is the oldest Botanical garden, botanic garden in Great Britain and one of the oldest scientific gardens in the world. The garden was founded in 1621 as a physic garden growing plants for medicinal resear ...

Oxford Oxford () is a City status in the United Kingdom, cathedral city and non-metropolitan district in Oxfordshire, England, of which it is the county town. The city is home to the University of Oxford, the List of oldest universities in continuou ...

, England and was soon spreading along the railways and throughout the country. It became near-extinct by the 1990s probably due to the use of weed-killing chemicals and ground disturbance. A programme of reintroduction in York resulted in flowering plants in 2023 and a sustainable population of several thousand plants.

Evolution

''Senecio eboracensis'' is a

hybrid species Hybrid speciation is a form of speciation where hybridization between two different species leads to a new species, reproductively isolated from the parent species. Previously, reproductive isolation between two species and their parents was tho ...

whose parents are the self-incompatible and promiscuous Sicilian ''

'' (also known as Oxford ragwort) and the self-compatible and tenacious ''

'' (also known as Common groundsel). Like ''S. vulgaris'', ''S. eboracensis'' is self-compatible but shows little or no natural crossing with its parent species and is therefore

reproductively isolated The mechanisms of reproductive isolation are a collection of evolutionary mechanisms, behaviors and physiological processes critical for speciation. They prevent members of different species from producing offspring, or ensure that any offsprin ...

, indicating that strong breeding barriers exist between this new hybrid and its parents. It is thought to have resulted from

backcrossing Backcrossing is a crossing of a hybrid with one of its parents or an individual genetically similar to its parent, to achieve offspring with a genetic identity closer to that of the parent. It is used in horticulture, animal breeding, and produc ...

of the

F1 hybrid F1 hybrid (also known as filial 1 hybrid) is the first filial generation of offspring of distinctly different parental types. F1 hybrids are used in genetics, and in selective breeding, where the term F1 crossbreed may be used. The term is somet ...

of its parents to ''S. vulgaris''. ''S. vulgaris'' is native to

Britain Britain most often refers to: * Great Britain, a large island comprising the countries of England, Scotland and Wales * The United Kingdom of Great Britain and Northern Ireland, a sovereign state in Europe comprising Great Britain and the north-eas ...

, while ''S. squalidus'' was introduced from

in the early 18th century; therefore, ''S. eboracensis'' has speciated from those two species within the last 300 years. Other hybrids descended from the same two parents are known. Some are infertile, such as ''S.'' x ''baxteri''. Other fertile hybrids are also known, including ''S. vulgaris'' var. ''hibernicus'' (which has been accepted as a synonym for ''S. vulgaris''), now common in Britain, and the

allohexaploid Polyploidy is a condition in which the cells of an organism have more than two paired sets of ( homologous) chromosomes. Most species whose cells have nuclei (eukaryotes) are diploid, meaning they have two complete sets of chromosomes, one fro ...

'' S. cambrensis'', which according to molecular evidence probably originated independently at least three times in different locations. Morphological and genetic evidence support the status of ''S. eboracensis'' as separate from other known hybrids.

References

External links

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