''Rhodiola'' is a genus of

perennial plant A perennial plant or simply perennial is a plant that lives more than two years. The term ('' per-'' + '' -ennial'', "through the years") is often used to differentiate a plant from shorter-lived annuals and biennials. The term is also wide ...

s in the family Crassulaceae that resemble '' Sedum'' and other members of the family. Like sedums, ''Rhodiola'' species are often called stonecrops. Some authors merge ''Rhodiola'' into ''Sedum''. ''Rhodiola'' species grow in high-altitude and other cold regions of the

Northern Hemisphere The Northern Hemisphere is the half of Earth that is north of the Equator. For other planets in the Solar System, north is defined as being in the same celestial hemisphere relative to the invariable plane of the solar system as Earth's Nort ...

. ''Den virtuella floran'' gives the number of species as 36, the Angiosperm Phylogeny Website gives it as 90, and the ''Flora of China'' gives it as about 90, with 55 in China and 16 endemic there. ''Flora of North America'' lists only three species in the United States and Canada.

Description

Among the distinguishing characters of the genus are two series of

stamen 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 filame ...

s totaling twice the number of

petal Petals are modified Leaf, leaves that surround the reproductive parts of flowers. They are often advertising coloration, brightly colored or unusually shaped to attract pollinators. All of the petals of a flower are collectively known as the ''c ...

s; free or nearly free petals (not joined in a tube); a stout

rhizome In botany and dendrology, a rhizome (; , ) is a modified subterranean plant stem that sends out roots and shoots from its nodes. Rhizomes are also called creeping rootstalks or just rootstalks. Rhizomes develop from axillary buds and grow hori ...

from whose

axils A leaf ( : leaves) is any of the principal appendages of a vascular plant stem, usually borne laterally aboveground and specialized for photosynthesis. Leaves are collectively called foliage, as in "autumn foliage", while the leaves, st ...

the flowering stems rise; and a basal rosette of leaves. This genus contains the only species of Crassulaceae that have unisexual flowers.

Phytochemistry

Rhodionin is a herbacetin rhamnoside found in ''Rhodiola'' species. * Rhodiolin 6831-53-0* Rhodiolgin 4696-39-6

Taxonomy

Although Linnaeus distinguished ''Rhodiola'' from '' Sedum'' on the basis of being

dioecious Dioecy (; ; adj. dioecious , ) is a characteristic of a species, meaning that it has distinct individual organisms (unisexual) that produce male or female gametes, either directly (in animals) or indirectly (in seed plants). Dioecious reproductio ...

, it was later submerged in the latter genus until the twentieth century, when it was restored, on the basis of well developed

rhizomes In botany and dendrology, a rhizome (; , ) is a modified subterranean plant stem that sends out roots and shoots from its nodes. Rhizomes are also called creeping rootstalks or just rootstalks. Rhizomes develop from axillary buds and grow hori ...

and annual flowering stems, arising from

of the scaly radical leaves. This separation was subsequently confirmed by

molecular phylogenetic Molecular phylogenetics () is the branch of phylogeny that analyzes genetic, hereditary molecular differences, predominantly in DNA sequences, to gain information on an organism's evolutionary relationships. From these analyses, it is possible to ...

studies. ''Rhodiola'' is placed within family Crassulaceae, in subfamily Sempervivoideae, tribe Umbiliceae. There it is a

sister group In phylogenetics, a sister group or sister taxon, also called an adelphotaxon, comprises the closest relative(s) of another given unit in an evolutionary tree. Definition The expression is most easily illustrated by a cladogram: Taxon A and t ...

to ''

Pseudosedum ''Pseudosedum'' is a genus of flowering plants in the family ''Crassulaceae''. Species the genus include: * ''Pseudosedum acutisepalum'' C.-A.Jansson * ''Pseudosedum affine'' (Schrenk) A.Berger * ''Pseudosedum bucharicum'' Boriss. * ''Pseudosedu ...

'', though some authors have suggested that the latter genus be submersed within ''Rhodiola''.

Subdivision

Traditionally ''Rhodiola'' was divided into subgenera, sections and series, based on plant characteristics. Four subgenera were recognised; ''Rhodiola'', ''Primuloides'', ''Crassipedes'' and ''Clementsia''. However molecular studies have failed to demonstrate

monophyly In cladistics for a group of organisms, monophyly is the condition of being a clade—that is, a group of taxa composed only of a common ancestor (or more precisely an ancestral population) and all of its lineal descendants. Monophyletic grou ...

of these subtaxa. Species include: *''

Rhodiola integrifolia ''Rhodiola integrifolia'' is a species of flowering plant in the stonecrop family known by the common names ledge stonecrop, western roseroot, and king's crown. It is native to north-easternmost Russia, including Kamchatka, and western North Ame ...

'' *''

Rhodiola crenulata ''Rhodiola'' is a genus of perennial plants in the family Crassulaceae that resemble ''Sedum'' and other members of the family. Like sedums, ''Rhodiola'' species are often called stonecrops. Some authors merge ''Rhodiola'' into ''Sedum''. '' ...

'' *''

Rhodiola cretinii ''Rhodiola'' is a genus of perennial plants in the family Crassulaceae that resemble ''Sedum'' and other members of the family. Like sedums, ''Rhodiola'' species are often called stonecrops. Some authors merge ''Rhodiola'' into ''Sedum''. '' ...

'' *''

Rhodiola imbricata ''Rhodiola'' is a genus of perennial plants in the family Crassulaceae that resemble ''Sedum'' and other members of the family. Like sedums, ''Rhodiola'' species are often called stonecrops. Some authors merge ''Rhodiola'' into ''Sedum''. '' ...

'' *'' Rhodiola kirilowii'' *''

Rhodiola rhodantha ''Rhodiola rhodantha'', common name redpod stonecrop or queen's crown, is a perennial flowering plant in the family Crassulaceae The Crassulaceae (from Latin ''crassus'', thick), also known as the stonecrop family or the orpine family, are a d ...

'' *''

Rhodiola rosea ''Rhodiola rosea'' (commonly golden root, rose root, roseroot, Aaron's rod, Arctic root, king's crown, ''lignum rhodium'', orpin rose) is a perennial flowering plant in the family Crassulaceae. It grows naturally in wild Arctic regions of Europe ...

'' *'' Rhodiola tibetica'' *'' Rhodiola quadrifida''

Etymology

The name combines the Greek ''rhodon'', meaning ''

rose A rose is either a woody perennial flowering plant of the genus ''Rosa'' (), in the family Rosaceae (), or the flower it bears. There are over three hundred species and tens of thousands of cultivars. They form a group of plants that can be ...

'' and referring to the rose-like smell of the roots, with the

Latin Latin (, or , ) is a classical language belonging to the Italic branch of the Indo-European languages. Latin was originally a dialect spoken in the lower Tiber area (then known as Latium) around present-day Rome, but through the power of the ...

diminutive A diminutive is a root word that has been modified to convey a slighter degree of its root meaning, either to convey the smallness of the object or quality named, or to convey a sense of intimacy or endearment. A (abbreviated ) is a word-formati ...

suffix ''-iola''.

Ecology

Dioecy Dioecy (; ; adj. dioecious , ) is a characteristic of a species, meaning that it has distinct individual organisms (unisexual) that produce male or female gametes, either directly (in animals) or indirectly (in seed plants). Dioecious reproductio ...

, having separate male and female flowers, has evolved at least three times in the genus, and reversals to a hermaphrodite condition have also occurred, which is a rare occurrence in flowering plants. It has been suggested that dioecy in the genus may correlate with abiotic pollination in the cold environment.

Uses

The

Holarctic The Holarctic realm is a biogeographic realm that comprises the majority of habitats found throughout the continents in the Northern Hemisphere. It corresponds to the floristic Boreal Kingdom. It includes both the Nearctic zoogeographical region ...

species ''

'' is used in

herbal medicine Herbal medicine (also herbalism) is the study of pharmacognosy and the use of medicinal plants, which are a basis of traditional medicine. With worldwide research into pharmacology, some herbal medicines have been translated into modern remed ...

. A number of species are grown as ornamentals, but growing them is difficult outside their native subarctic and alpine climates. In TCM, Rhodiola is known as Hong Jing Tian (红景天) and is used for fatigue, hypoxia, radiation, etc.

References

Bibliography

* * , ''see also''

Species Plantarum ' (Latin for "The Species of Plants") is a book by Carl Linnaeus, originally published in 1753, which lists every species of plant known at the time, classified into genera. It is the first work to consistently apply binomial names and was the ...

* '
full text at
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ResearchGate ResearchGate is a European commercial social networking site for scientists and researchers to share papers, ask and answer questions, and find collaborators. According to a 2014 study by ''Nature'' and a 2016 article in ''Times Higher Education'' ...

) * * * * (''see also'' Angiosperm Phylogeny Website) {{Taxonbar, from=Q133592 Crassulaceae Crassulaceae genera