''Rheum nobile'', the Sikkim rhubarb or noble rhubarb or पदमचाल, is a giant herbaceous

plant Plants are predominantly photosynthetic eukaryotes of the kingdom Plantae. Historically, the plant kingdom encompassed all living things that were not animals, and included algae and fungi; however, all current definitions of Plantae exclu ...

native to the

Himalaya The Himalayas, or Himalaya (; ; ), is a mountain range in Asia, separating the plains of the Indian subcontinent from the Tibetan Plateau. The range has some of the planet's highest peaks, including the very highest, Mount Everest. Over 100 ...

, from northeastern

Afghanistan Afghanistan, officially the Islamic Emirate of Afghanistan,; prs, امارت اسلامی افغانستان is a landlocked country located at the crossroads of Central Asia and South Asia. Referred to as the Heart of Asia, it is bordere ...

, east through northern

Pakistan Pakistan ( ur, ), officially the Islamic Republic of Pakistan ( ur, , label=none), is a country in South Asia. It is the world's fifth-most populous country, with a population of almost 243 million people, and has the world's second-lar ...

and

India India, officially the Republic of India (Hindi: ), is a country in South Asia. It is the seventh-largest country by area, the second-most populous country, and the most populous democracy in the world. Bounded by the Indian Ocean on the so ...

Nepal Nepal (; ne, :ne:नेपाल, नेपाल ), formerly the Federal Democratic Republic of Nepal ( ne, सङ्घीय लोकतान्त्रिक गणतन्त्र नेपाल ), is a landlocked country in S ...

Sikkim Sikkim (; ) is a state in Northeastern India. It borders the Tibet Autonomous Region of China in the north and northeast, Bhutan in the east, Province No. 1 of Nepal in the west and West Bengal in the south. Sikkim is also close to the Silig ...

(in India),

Bhutan Bhutan (; dz, འབྲུག་ཡུལ་, Druk Yul ), officially the Kingdom of Bhutan,), is a landlocked country in South Asia. It is situated in the Eastern Himalayas, between China in the north and India in the south. A mountainou ...

, and

Tibet Tibet (; ''Böd''; ) is a region in East Asia, covering much of the Tibetan Plateau and spanning about . It is the traditional homeland of the Tibetan people. Also resident on the plateau are some other ethnic groups such as Monpa, Taman ...

Myanmar Myanmar, ; UK pronunciations: US pronunciations incl. . Note: Wikipedia's IPA conventions require indicating /r/ even in British English although only some British English speakers pronounce r at the end of syllables. As John Wells explai ...

, occurring in the

alpine zone Alpine tundra is a type of natural region or biome that does not contain trees because it is at high elevation, with an associated alpine climate, harsh climate. As the latitude of a location approaches the poles, the threshold elevation for alp ...

at 4000–4800 m

altitude Altitude or height (also sometimes known as depth) is a distance measurement, usually in the vertical or "up" direction, between a reference datum and a point or object. The exact definition and reference datum varies according to the context ...

. It is an extraordinary species of rhubarb (genus ''

Rheum Rheum (; from Greek: ῥεῦμα ''rheuma'' 'a flowing, rheum') is a thin mucus naturally discharged from the eyes, nose, or mouth, often during sleep (cf. mucopurulent discharge).Amodio, Aime"Where Do Eye Boogers Come From?" Families.com bl ...

''). At 1–2 m tall, the

monocarpic Monocarpic plants are those that flower and set seeds only once, and then die. The term is derived from Greek (''mono'', "single" + ''karpos'', "fruit" or "grain"), and was first used by Alphonse de Candolle. Other terms with the same meaning ar ...

inflorescences of ''R. nobile'' tower above the other shrubs and low herbs in its habitat, and it is visible across valleys a mile away. ''R. nobile'' is often called a ''glasshouse plant'' because of its outer curtain of translucent bracts which pass visible light, creating a

greenhouse effect The greenhouse effect is a process that occurs when energy from a planet's host star goes through the planet's atmosphere and heats the planet's surface, but greenhouse gases in the atmosphere prevent some of the heat from returning directly ...

, while blocking

ultraviolet Ultraviolet (UV) is a form of electromagnetic radiation with wavelength from 10 nm (with a corresponding frequency around 30 PHz) to 400 nm (750 THz), shorter than that of visible light, but longer than X-rays. UV radiation ...

radiation. These are likely defenses against the increased UV-B exposure and extreme cold in its high altitude range.Iwashina et al. p.101

Description

An individual ''R. nobile'' is a conical tower of delicate, straw-coloured, shining, translucent, regularly overlapping bracts; the higher ones have pink edges. Large, glossy, green

radicle In botany, the radicle is the first part of a seedling (a growing plant embryo) to emerge from the seed during the process of germination. The radicle is the embryonic root of the plant, and grows downward in the soil (the shoot emerges from ...

leaves, with red petioles and nerves, form a broad base to the plant. Turning up the bracts reveals membranous, fragile, pink

stipule In botany, a stipule is an outgrowth typically borne on both sides (sometimes on just one side) of the base of a leafstalk (the petiole). Stipules are considered part of the anatomy of the leaf of a typical flowering plant, although in many speci ...

s. Within these are short branched panicles of diminutive green

flower A flower, sometimes known as a bloom or blossom, is the reproductive structure found in flowering plants (plants of the division Angiospermae). The biological function of a flower is to facilitate reproduction, usually by providing a mechani ...

s.Hooker p.94 The

root In vascular plants, the roots are the organs of a plant that are modified to provide anchorage for the plant and take in water and nutrients into the plant body, which allows plants to grow taller and faster. They are most often below the su ...

is often long and as thick as an arm, and bright yellow inside. After flowering, the stem lengthens and the bracts separate one from another, turning a coarse red-brown. As the fruit ripens, the bracts fall away, leaving a ragged-looking stem covered with panicles of deep brown pendulous fruits. As Hooker put their appearance: ''"In the winter, these naked black stems, projecting from the beetling cliffs, or towering above the snow, are in dismal keeping with the surrounding desolation of that season."''

Karyotypy

''R. nobile'' has a

chromosome A chromosome is a long DNA molecule with part or all of the genetic material of an organism. In most chromosomes the very long thin DNA fibers are coated with packaging proteins; in eukaryotic cells the most important of these proteins are ...

count of 2''n''=22.

Bracts

The bracts of ''R. nobile'' are 110-170 µm thick and do not differentiate into palisade and spongy layers. They selectively block

ultraviolet radiation Ultraviolet (UV) is a form of electromagnetic radiation with wavelength from 10 nm (with a corresponding frequency around 30 PHz) to 400 nm (750 THz), shorter than that of visible light, but longer than X-rays. UV radiation i ...

while letting almost all visible light through; thus the developing flowers and the

apical meristem The meristem is a type of tissue found in plants. It consists of undifferentiated cells (meristematic cells) capable of cell division. Cells in the meristem can develop into all the other tissues and organs that occur in plants. These cells conti ...

are protected from the intense radiation found in high altitudes. The major UV blockers found in the bracts are all

quercetin Quercetin is a plant flavonol from the flavonoid group of polyphenols. It is found in many fruits, vegetables, leaves, seeds, and grains; capers, red onions, and kale are common foods containing appreciable amounts of it. It has a bitter flavor ...

flavonoids:Iwashina et al. 104-106 *

Rutin Rutin, also called rutoside, quercetin-3-O-rutinoside and sophorin, is the glycoside combining the flavonol quercetin and the disaccharide rutinose (α-L-rhamnopyranosyl-(1→6)-β-D-glucopyranose). It is a flavonoid found in a wide variety of pl ...

, quercetin 3-''O''-

rutinoside Rutinose is the disaccharide also known as 6-''O''-α-L- rhamnosyl-D-glucose (C12H22O10) that is present in some flavonoid glycosides. It is prepared from rutin by hydrolysis Hydrolysis (; ) is any chemical reaction in which a molecule of wa ...

: widespread in higher plants and previously reported in leaves and petioles of other ''Rheum'' species * Guaijaverin, quercetin 3-''O''-

arabinoside Arabinose is an aldopentose – a monosaccharide containing five carbon atoms, and including an aldehyde (CHO) functional group. For biosynthetic reasons, most saccharides are almost always more abundant in nature as the "D"-form, or structurally ...

: first report in ''Rheum'' * Hyperin, quercetin 3-''O''-

galactoside A galactoside is a glycoside containing galactose. The H of the OH group on carbon-1 of galactose is replaced by an organic moiety. Depending on whether the glycosidic bond lies "above" or "below" the plane of the galactose molecule, galactosides ...

: widespread in plants and previously reported in leaves and petioles of '' R. rhaponticum'' *

Isoquercitrin Isoquercetin, isoquercitrin or isotrifoliin is a flavonoid, a type of chemical compound. It is the 3-''O''-glucoside of quercetin. Isoquercitrin can be isolated from various plant species including ''Mangifera indica'' (mango) and ''Rheum nobile'' ...

3-''O''- glucoside: widespread in plants and previously reported in leaves and petioles of ''R. rhaponticum'' *Quercetin 3-''O''- ″-(3-hydroxy-3-methylglutaroyl)-glucoside first finding in nature Minor UV blockers include quercetin 7-''O''-

glycoside In chemistry, a glycoside is a molecule in which a sugar is bound to another functional group via a glycosidic bond. Glycosides play numerous important roles in living organisms. Many plants store chemicals in the form of inactive glycoside ...

itself,

kaempferol Kaempferol (3,4′,5,7-tetrahydroxyflavone) is a natural flavonol, a type of flavonoid, found in a variety of plants and plant-derived foods including kale, beans, tea, spinach, and broccoli. Kaempferol is a yellow crystalline solid with a meltin ...

glycoside, and feruloyl

ester In chemistry, an ester is a compound derived from an oxoacid (organic or inorganic) in which at least one hydroxyl group () is replaced by an alkoxy group (), as in the substitution reaction of a carboxylic acid and an alcohol. Glycerides a ...

Edibility

The stems are pleasantly

acidic In computer science, ACID ( atomicity, consistency, isolation, durability) is a set of properties of database transactions intended to guarantee data validity despite errors, power failures, and other mishaps. In the context of databases, a ...

, and they are consumed by the local people, who call the plant ''Chuka''. The hollow of the stem contains a good deal of limpid water.

History

A description of ''R. nobile'' was first published by

Joseph Dalton Hooker Sir Joseph Dalton Hooker (30 June 1817 – 10 December 1911) was a British botanist and explorer in the 19th century. He was a founder of geographical botany and Charles Darwin's closest friend. For twenty years he served as director of ...

and

Thomas Thomson Thomas Thomson may refer to: * Tom Thomson (1877–1917), Canadian painter * Thomas Thomson (apothecary) (died 1572), Scottish apothecary * Thomas Thomson (advocate) (1768–1852), Scottish lawyer * Thomas Thomson (botanist) (1817–1878), Scottis ...

in 1855. Hooker wrote: :"The present is certainly the most striking of the many fine alpine plants of

; and though in every botanical character, as also in the acid juice of the stem, a genuine Rhubarb, it differs so remarkably in habit and general appearance from any of its congeners, that at first sight it could not be recognized as one of them. I first saw it from a distance of fully a mile, dotting the black cliffs of the Lachen

valley A valley is an elongated low area often running between hills or mountains, which will typically contain a river or stream running from one end to the other. Most valleys are formed by erosion of the land surface by rivers or streams ove ...

at elevation, in inaccessible situations, and was quite at a loss to conceive what it could be; not was it till I had turned back the curious bracteal leaves and examined the flowers that I was persuaded of its being a true Rhubarb."

References

* * *

Notes

External links

Plants For A Future

Photos by Thomas Kornack
{{Taxonbar, from=Q721018 nobile Flora of Tibet Flora of Myanmar Flora of the Indian subcontinent