''Karpatiosorbus houstoniae'', or Houston's whitebeam, is a hybrid of two deciduous trees: the common whitebeam (''

Sorbus aria ''Sorbus aria'' (syn. ''Aria nivea''), the whitebeam or common whitebeam, is a deciduous tree, the type species of the subgenus ''Sorbus'' subg. ''Aria'' of the genus ''Sorbus''. It is native to most of Europe as well as North Africa (Algeria, Mo ...

'') and the Bristol whitebeam (''

Karpatiosorbus bristoliensis ''Karpatiosorbus bristoliensis'' is a species of flowering plant in the family Rosaceae. It is known commonly as the Bristol whitebeam. It is endemic to Great Britain, growing wild only in the Avon Gorge and in the Leigh Woods area of Bristol ...

''). Only a single example of the

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 ...

is known to exist, at the

Avon Gorge The Avon Gorge () is a 1.5-mile (2.5-kilometre) long gorge on the River Avon in Bristol, England. The gorge runs south to north through a limestone ridge west of Bristol city centre, and about 3 miles (5 km) from the mouth of the r ...

in Bristol, England. The only specimen grows on a cliff below

Stokeleigh Camp Stokeleigh Camp is an Iron Age promontory fort in Leigh Woods North Somerset near Bristol, England. The hill fort is one of three Iron Age fortifications overlooking the Avon Gorge, the others being Burgh Walls Camp south of the Nightingale Val ...

Leigh Woods Leigh Woods is a area of woodland on the south-west side of the Avon Gorge, close to the Clifton Suspension Bridge, within North Somerset opposite the English city of Bristol and north of the Ashton Court estate, of which it formed a part. S ...

North Somerset North Somerset is a unitary district in Somerset, South West England. Whilst its area covers part of the ceremonial county of Somerset, it is administered independently of the non-metropolitan county. Its administrative headquarters is in the ...

and cannot be accessed without ropes.

Description

The specimen is a small tree, at least in height. Buds are oval to conical. The leaves of Houston's whitebeam have a similarity to those of Bristol whitebeam, although they are wider. The leaves are teardrop-shaped to teardrop-oval, and about 1.5 times as long as wide, with an apex that tapers to a long point and a base that is relatively wide. The leaves are shallowly, acutely lobed, 7–14% of the way to the central vein. The leaf margins are weakly doubly serrate. The upper surface is dark green and hairless, the lower greenish-white with matted plant hairs and between 17 and 22 veins that project at an angle of 32 to 39 degrees from the central vein. The petioles are in length. The

inflorescence An inflorescence is a group or cluster of flowers arranged on a stem that is composed of a main branch or a complicated arrangement of branches. Morphologically, it is the modified part of the shoot of seed plants where flowers are formed ...

measures up to in diameter, with individual flowers in diameter. The fragrant flowers have

sepals 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 b ...

that are narrow and triangular, and white petals that are widely oval to nearly round, x . The

stamens The stamen (plural ''stamina'' or ''stamens'') is the pollen-producing reproductive organ of a flower. Collectively the stamens form the androecium., p. 10 Morphology and terminology A stamen typically consists of a stalk called the filam ...

are pink. The fruit are generally round, the largest up to in diameter; mature fruit are orange-red with fully formed seeds. There is a moderate number of

lenticels A lenticel is a porous tissue consisting of cells with large intercellular spaces in the periderm of the secondarily thickened organs and the bark of woody stems and roots of dicotyledonous flowering plants. It functions as a pore, providing a ...

Discovery

Houston's whitebeam was discovered by

Libby Houston Libby Houston is an English poet, botanist, and rock climber. The native of North London has published several collections of poetry. Houston, a research associate at the School of Biological Sciences at the University of Bristol, has discovere ...

, a research associate at the

University of Bristol The University of Bristol is a Red brick university, red brick Russell Group research university in Bristol, England. It received its royal charter in 1909, although it can trace its roots to a Society of Merchant Venturers, Merchant Venturers' sc ...

School of Biological Sciences. The rock climber found the rare hybrid on a

Carboniferous Limestone Carboniferous Limestone is a collective term for the succession of limestones occurring widely throughout Great Britain and Ireland that were deposited during the Dinantian Epoch of the Carboniferous Period. These rocks formed between 363 ...

cliff at Avon Gorge in 2005. DNA analysis of nuclear

microsatellites A microsatellite is a tract of repetitive DNA in which certain DNA motifs (ranging in length from one to six or more base pairs) are repeated, typically 5–50 times. Microsatellites occur at thousands of locations within an organism's genome. ...

at the University of Bristol was performed and confirmed the nature of the new hybrid. The tree was officially named after Houston in February 2009 in Volume 27, Part 3 of Watsonia, the journal of the

Botanical Society of the British Isles The Botanical Society of Britain and Ireland (BSBI) is a scientific society for the study of flora, plant distribution and taxonomy relating to Great Britain, Ireland, the Channel Islands and the Isle of Man. The society was founded as the Botani ...

. It is a member of the

Sorbus latifolia ''Sorbus'' is a genus of over 100 species of trees and shrubs in the rose family, Rosaceae. Species of ''Sorbus'' (''s.l.'') are commonly known as whitebeam, rowan (mountain-ash) and service tree. The exact number of species is disputed depen ...

group. The Somerset Rare Plants Group indicates that the tree's

Red List The International Union for Conservation of Nature (IUCN) Red List of Threatened Species, also known as the IUCN Red List or Red Data Book, founded in 1964, is the world's most comprehensive inventory of the global conservation status of biolog ...

status is critically endangered, although the site of the

International Union for Conservation of Nature The International Union for Conservation of Nature (IUCN; officially International Union for Conservation of Nature and Natural Resources) is an international organization working in the field of nature conservation and sustainable use of natur ...

(IUCN) indicates that the tree has not yet been assessed for the list, but is in the

Catalogue of Life The Catalogue of Life is an online database that provides an index of known species of animals, plants, fungi, and microorganisms. It was created in 2001 as a partnership between the global Species 2000 and the American Integrated Taxonomic I ...

. The short film, ''Houston's Whitebeam'' ''(link below)'', which related the discovery of the tree, was a finalist in the ONSIGHT & Panasonic contest "Bristol's Best Kept Secret" at the

Wildscreen Film Festival Wildscreen is a wildlife conservation charity based in Bristol, England. The charity was founded in December 1987 from a trust which had operated since 1982, with the initial aim of encouraging and applauding excellence in the production of na ...

in 2008. The filmmaker proposed that Houston's whitebeam was Bristol's best kept secret. The festival, hosted every two years by Bristol, was founded in 1982 and is dedicated to "celebrating, applauding and encouraging excellence and responsibility within the wildlife and environmental filmmaking industry."

References

External links

''Houston's Whitebeam'', short film

Photograph of Libby Houston and Houston's Whitebeam, 2009
{{DEFAULTSORT:Karpatiosorbus houstoniae houstoniae Environment of Bristol North Somerset Plant nothospecies