Roscoea
Encyclopedia
Roscoea is a genus of perennial plant
s of the family
Zingiberaceae
(the ginger
family). Most members of the family are tropical, whereas Roscoea species are native to mountainous regions of the Himalayas
, China
and its southern neighbours. Roscoea flowers superficially resemble orchids, although they are not related. Some species are grown as ornamental plants in gardens.
through the Himalayas to Vietnam
, extending northwards into China
. There are up to 22 recognized species, of which 8 are endemic to China. Typically they grow in grassland, in screes or on the edges of deciduous woodland at heights of 1200–5000 m (3,937–16,404.2 ft), coming into growth at the start of the monsoon season.
Species of Roscoea are small perennial herbaceous plant
s. They die back each year to a short vertical rhizome
, to which the tuberous roots
are attached. Like many members of the Zingiberales
(the order
to which the gingers belong), Roscoea has "pseudostems": structures which resemble stems but are actually formed from the tightly wrapped bases of its leaves ("sheaths"). The leaves are without a stalk (petiole
). Lower leaves may consist solely of a sheath; upper leaves have a blade which is free from the pseudostem, and is oblong or lanceolate (i.e. considerably longer than it is wide). The relative number of bladeless versus complete leaves is one distinguishing feature of the two clade
s into which the genus is divided.
The flowers are borne in a spike at the end of the pseudostems. Like other members of the ginger family (Zingiberaceae), Roscoea flowers have a complex structure (superficially resembling that of an orchid). Each flower has a tube-shaped outer calyx, which is split on one side and ends in two or three teeth. The petals are joined together at the base, and then divide into three lobes. The central lobe is upright and usually forms a hood; the two side lobes are narrower than the central one. The flower then has what appear to be three inner petals, which are actually formed from four sterile stamen
s (staminodes). Two lateral staminodes form what look like upright petals, often also hooded in shape; two other staminodes are fused together to form a prominent central "lip" or labellum.
The single fertile stamen has a short filament bearing a cylindrical anther. The connective tissue between the anther's two pollen sacs extends outwards at its base to form spurs. The ovary
has three "cells" or locules, eventually producing many small arillate
seeds. The single functional style extends upwards through a grove in the stamen to appear above its top.
by long-tongued insects specializing in this type of flower. The design of the flower suggests that the lip acts as a landing platform and that if a pollinator puts its head into the flower in order to obtain nectar, it will push down on the spurs on the stamen, causing the anther (and the stigma which is held in front of it) to bend over and contact the insect's back. However, in the only two species so far studied in detail (R. cautleyoides and R. humeana), the actual pollinators were short-tongued pollen-collecting bees. In at least one species, R. schneideriana, it has been shown that if cross-pollination does not occur, the stigma bends over towards the anthers, thus effecting self-pollination. One suggestion is that although the original pollinators may have been long-tongued insects, these are now absent from at least some of the areas where Roscoea occurs, so that the genus has been able to survive in its alpine habitats through the presence of generalist pollinators and self-compatibility.
in 1806. The type species is R. purpurea
. The name honours Smith's friend William Roscoe
, the founder of the Liverpool Botanic Garden (now relocated to the Wavertree Botanic Gardens). Roscoe is known to have been interested in "gingers" (Zingiberales) and to have grown a number of collections of this group of plants.
may have evolved relatively recently and be a response to the uplift taking place in the region in the last 50 million years or so due to the collision of the Indian and Asian tectonic plates
.
A molecular phylogenetic analysis of 15 species of Roscoea, based on nuclear ribosomal DNA
, showed that the genus was monophyletic
, and distinct from the closely related genus Cautleya. The 15 species fell into two clear groups, a Himalayan clade and a Chinese clade (which includes one species from Burma). The two clades correspond to a geographical separation, being divided by the Brahmaputra River
as it flows south at the end of the Himalayan mountain chain. It has been suggested that the genus may have originated in this area and then spread westwards along the Himalayas and eastwards into the mountains of China and its southern neighbours.
The material of R. tibetica included in the analysis came from Chinese sources. Later research showed that plants from Bhutan and southern Tibet which had previously been considered to be R. tibetica were actually a new species, R. bhutanica
, which belongs to the Himalayan clade. There are few clear-cut morphological differences between the two clades; one is that compared to the Himalayan group, members of the Chinese clade have a larger number of bladeless leaves (i.e. leaves which have only a sheath forming part of the pseudostem).
The hybrid R. auriculata × R. cautleyoides has occurred in cultivation, and has been given the name R. × beesiana Cowley & C.Whitehouse.
They can be propagated by careful division of the individual growth points produced by a large plant, or by seed. Seed should not be allowed to dry out. If sown immediately it is ripe, it will normally germinate in the following summer. Young plants should be potted on before the tuberous roots become too intertwined.
Perennial plant
A perennial plant or simply perennial is a plant that lives for more than two years. The term is often used to differentiate a plant from shorter lived annuals and biennials. The term is sometimes misused by commercial gardeners or horticulturalists to describe only herbaceous perennials...
s of the family
Family (biology)
In biological classification, family is* a taxonomic rank. Other well-known ranks are life, domain, kingdom, phylum, class, order, genus, and species, with family fitting between order and genus. As for the other well-known ranks, there is the option of an immediately lower rank, indicated by the...
Zingiberaceae
Zingiberaceae
Zingiberaceae, or the Ginger family, is a family of flowering plants consisting of aromatic perennial herbs with creeping horizontal or tuberous rhizomes, comprising ca. 52 genera and more than 1300 species, distributed throughout tropical Africa, Asia, and the Americas.Many species are important...
(the ginger
Ginger
Ginger is the rhizome of the plant Zingiber officinale, consumed as a delicacy, medicine, or spice. It lends its name to its genus and family . Other notable members of this plant family are turmeric, cardamom, and galangal....
family). Most members of the family are tropical, whereas Roscoea species are native to mountainous regions of the Himalayas
Himalayas
The Himalaya Range or Himalaya Mountains Sanskrit: Devanagari: हिमालय, literally "abode of snow"), usually called the Himalayas or Himalaya for short, is a mountain range in Asia, separating the Indian subcontinent from the Tibetan Plateau...
, China
China
Chinese civilization may refer to:* China for more general discussion of the country.* Chinese culture* Greater China, the transnational community of ethnic Chinese.* History of China* Sinosphere, the area historically affected by Chinese culture...
and its southern neighbours. Roscoea flowers superficially resemble orchids, although they are not related. Some species are grown as ornamental plants in gardens.
Description
Roscoea is found from KashmirKashmir
Kashmir is the northwestern region of the Indian subcontinent. Until the mid-19th century, the term Kashmir geographically denoted only the valley between the Great Himalayas and the Pir Panjal mountain range...
through the Himalayas to Vietnam
Vietnam
Vietnam – sometimes spelled Viet Nam , officially the Socialist Republic of Vietnam – is the easternmost country on the Indochina Peninsula in Southeast Asia. It is bordered by China to the north, Laos to the northwest, Cambodia to the southwest, and the South China Sea –...
, extending northwards into China
China
Chinese civilization may refer to:* China for more general discussion of the country.* Chinese culture* Greater China, the transnational community of ethnic Chinese.* History of China* Sinosphere, the area historically affected by Chinese culture...
. There are up to 22 recognized species, of which 8 are endemic to China. Typically they grow in grassland, in screes or on the edges of deciduous woodland at heights of 1200–5000 m (3,937–16,404.2 ft), coming into growth at the start of the monsoon season.
Species of Roscoea are small perennial herbaceous plant
Herbaceous plant
A herbaceous plant is a plant that has leaves and stems that die down at the end of the growing season to the soil level. They have no persistent woody stem above ground...
s. They die back each year to a short vertical rhizome
Rhizome
In botany and dendrology, a rhizome is a characteristically horizontal stem of a plant that is usually found underground, often sending out roots and shoots from its nodes...
, to which the tuberous roots
Tuber
Tubers are various types of modified plant structures that are enlarged to store nutrients. They are used by plants to survive the winter or dry months and provide energy and nutrients for regrowth during the next growing season and they are a means of asexual reproduction...
are attached. Like many members of the Zingiberales
Zingiberales
Zingiberales is an order of flowering plants. The order has been widely recognised by the taxonomists, at least for the past few decades. This order includes many familiar plants like ginger, cardamom, turmeric, galangal and myoga of the Zingiberaceae or ginger family, and bananas and plantains...
(the order
Order (biology)
In scientific classification used in biology, the order is# a taxonomic rank used in the classification of organisms. Other well-known ranks are life, domain, kingdom, phylum, class, family, genus, and species, with order fitting in between class and family...
to which the gingers belong), Roscoea has "pseudostems": structures which resemble stems but are actually formed from the tightly wrapped bases of its leaves ("sheaths"). The leaves are without a stalk (petiole
Petiole (botany)
In botany, the petiole is the stalk attaching the leaf blade to the stem. The petiole usually has the same internal structure as the stem. Outgrowths appearing on each side of the petiole are called stipules. Leaves lacking a petiole are called sessile, or clasping when they partly surround the...
). Lower leaves may consist solely of a sheath; upper leaves have a blade which is free from the pseudostem, and is oblong or lanceolate (i.e. considerably longer than it is wide). The relative number of bladeless versus complete leaves is one distinguishing feature of the two clade
Clade
A clade is a group consisting of a species and all its descendants. In the terms of biological systematics, a clade is a single "branch" on the "tree of life". The idea that such a "natural group" of organisms should be grouped together and given a taxonomic name is central to biological...
s into which the genus is divided.
The flowers are borne in a spike at the end of the pseudostems. Like other members of the ginger family (Zingiberaceae), Roscoea flowers have a complex structure (superficially resembling that of an orchid). Each flower has a tube-shaped outer calyx, which is split on one side and ends in two or three teeth. The petals are joined together at the base, and then divide into three lobes. The central lobe is upright and usually forms a hood; the two side lobes are narrower than the central one. The flower then has what appear to be three inner petals, which are actually formed from four sterile stamen
Stamen
The stamen is the pollen producing reproductive organ of a flower...
s (staminodes). Two lateral staminodes form what look like upright petals, often also hooded in shape; two other staminodes are fused together to form a prominent central "lip" or labellum.
The single fertile stamen has a short filament bearing a cylindrical anther. The connective tissue between the anther's two pollen sacs extends outwards at its base to form spurs. The ovary
Ovary
The ovary is an ovum-producing reproductive organ, often found in pairs as part of the vertebrate female reproductive system. Ovaries in anatomically female individuals are analogous to testes in anatomically male individuals, in that they are both gonads and endocrine glands.-Human anatomy:Ovaries...
has three "cells" or locules, eventually producing many small arillate
Aril
An aril is any specialized outgrowth from the funiculus that covers or is attached to the seed. It is sometimes applied to any appendage or thickening of the seed coat in flowering plants, such as the edible parts of the mangosteen and pomegranate fruit, the mace of the nutmeg seed, or the...
seeds. The single functional style extends upwards through a grove in the stamen to appear above its top.
Flower structure and pollination
The orchid-like flowers with a long floral tube appear to be an adaptation for pollinationPollination
Pollination is the process by which pollen is transferred in plants, thereby enabling fertilisation and sexual reproduction. Pollen grains transport the male gametes to where the female gamete are contained within the carpel; in gymnosperms the pollen is directly applied to the ovule itself...
by long-tongued insects specializing in this type of flower. The design of the flower suggests that the lip acts as a landing platform and that if a pollinator puts its head into the flower in order to obtain nectar, it will push down on the spurs on the stamen, causing the anther (and the stigma which is held in front of it) to bend over and contact the insect's back. However, in the only two species so far studied in detail (R. cautleyoides and R. humeana), the actual pollinators were short-tongued pollen-collecting bees. In at least one species, R. schneideriana, it has been shown that if cross-pollination does not occur, the stigma bends over towards the anthers, thus effecting self-pollination. One suggestion is that although the original pollinators may have been long-tongued insects, these are now absent from at least some of the areas where Roscoea occurs, so that the genus has been able to survive in its alpine habitats through the presence of generalist pollinators and self-compatibility.
Taxonomy
Roscoea was named by the English botanist James Edward SmithJames Edward Smith
Sir James Edward Smith was an English botanist and founder of the Linnean Society.Smith was born in Norwich in 1759, the son of a wealthy wool merchant. He displayed a precocious interest in the natural world...
in 1806. The type species is R. purpurea
Roscoea purpurea
Roscoea purpurea is a perennial herbaceous plant occurring in the Himalayas, particularly Nepal. Most members of the ginger family , to which it belongs, are tropical, but species of Roscoea grow in much colder mountainous regions...
. The name honours Smith's friend William Roscoe
William Roscoe
William Roscoe , was an English historian and miscellaneous writer.-Life:He was born in Liverpool, where his father, a market gardener, kept a public house called the Bowling Green at Mount Pleasant. Roscoe left school at the age of twelve, having learned all that his schoolmaster could teach...
, the founder of the Liverpool Botanic Garden (now relocated to the Wavertree Botanic Gardens). Roscoe is known to have been interested in "gingers" (Zingiberales) and to have grown a number of collections of this group of plants.
Evolution and phylogeny
The Zingiberaceae family is mainly tropical in distribution. The unusual mountainous distribution of Roscoea and closely related genera such as CautleyaCautleya
Cautleya is a small genus consisting of 3–4 species of high-altitude tropical and temperate exotic jungle gingers, native to cool forest areas of the eastern Himalayas. The plants produce popular tropical flowers widely used in the cut flower industry. They are deciduous and winter dormant. The...
may have evolved relatively recently and be a response to the uplift taking place in the region in the last 50 million years or so due to the collision of the Indian and Asian tectonic plates
Plate tectonics
Plate tectonics is a scientific theory that describes the large scale motions of Earth's lithosphere...
.
A molecular phylogenetic analysis of 15 species of Roscoea, based on nuclear ribosomal DNA
Ribosomal DNA
Ribosomal DNA codes for ribosomal RNA. The ribosome is an intracellular macromolecule that produces proteins or polypeptide chains. The ribosome itself consists of a composite of proteins and RNA. As shown in the figure, rDNA consists of a tandem repeat of a unit segment, an operon, composed of...
, showed that the genus was monophyletic
Monophyly
In common cladistic usage, a monophyletic group is a taxon which forms a clade, meaning that it contains all the descendants of the possibly hypothetical closest common ancestor of the members of the group. The term is synonymous with the uncommon term holophyly...
, and distinct from the closely related genus Cautleya. The 15 species fell into two clear groups, a Himalayan clade and a Chinese clade (which includes one species from Burma). The two clades correspond to a geographical separation, being divided by the Brahmaputra River
Brahmaputra River
The Brahmaputra , also called Tsangpo-Brahmaputra, is a trans-boundary river and one of the major rivers of Asia. It is the only Indian river that is attributed the masculine gender and thus referred to as a in Indo-Aryan languages and languages with Indo-Aryan influence...
as it flows south at the end of the Himalayan mountain chain. It has been suggested that the genus may have originated in this area and then spread westwards along the Himalayas and eastwards into the mountains of China and its southern neighbours.
The material of R. tibetica included in the analysis came from Chinese sources. Later research showed that plants from Bhutan and southern Tibet which had previously been considered to be R. tibetica were actually a new species, R. bhutanica
Roscoea bhutanica
Roscoea bhutanica is a perennial herbaceous plant native to the mountains of Bhutan and Tibet. Formerly regarded as part of Roscoea tibetica, it was recognized as a separate species in 2000. Most members of the ginger family , to which it belongs, are tropical, but R...
, which belongs to the Himalayan clade. There are few clear-cut morphological differences between the two clades; one is that compared to the Himalayan group, members of the Chinese clade have a larger number of bladeless leaves (i.e. leaves which have only a sheath forming part of the pseudostem).
Species
, the World Checklist of Selected Plant Families accepts the following species of Roscoea:- Roscoea alpinaRoscoea alpinaRoscoea alpina is a perennial herbaceous plant native to the Himalayas, from Kashmir to Burma. Most members of the ginger family , to which it belongs, are tropical, but R. forrestii, like other species of Roscoea, grows in much colder mountainous regions...
Royle - Roscoea auriculataRoscoea auriculataRoscoea auriculata is a perennial herbaceous plant occurring in the eastern Himalayas, in Tibet, Bhutan, Nepal and Sikkim. Most members of the ginger family , to which it belongs, are tropical, but R. auriculata, like other species of Roscoea, grows in much colder mountainous regions...
K.Schum. - Roscoea australis Cowley
- Roscoea bhutanicaRoscoea bhutanicaRoscoea bhutanica is a perennial herbaceous plant native to the mountains of Bhutan and Tibet. Formerly regarded as part of Roscoea tibetica, it was recognized as a separate species in 2000. Most members of the ginger family , to which it belongs, are tropical, but R...
Ngamr. - Roscoea brandisii (King ex Baker) K.Schum.
- Roscoea cangshanensisRoscoea cangshanensisRoscoea cangshanensis is a perennial herbaceous plant native to the mountains of China, being found in Yunnan. Most members of the ginger family , to which it belongs, are tropical, but R...
M.H.Luo, X.F.Gao & H.H.Lin - Roscoea capitataRoscoea capitataRoscoea capitata is a perennial herbaceous plant native to the Himalayas, being found in Nepal. Most members of the ginger family , to which it belongs, are tropical, but R...
Sm. - Roscoea cautleyoidesRoscoea cautleyoidesRoscoea cautleyoides is a perennial herbaceous plant occurring in the Sichuan and Yunnan provinces of China. The scientific name is also spelt Roscoea cautleoides . Most members of the ginger family , to which it belongs, are tropical, but R. cautleyoides, like other species of Roscoea, grows in...
Gagnep. - Roscoea debilis Gagnep.
- Roscoea forrestiiRoscoea forrestiiRoscoea forrestii is a perennial herbaceous plant occurring in the Sichuan and Yunnan provinces of China. Most members of the ginger family , to which it belongs, are tropical, but R. forrestii, like other species of Roscoea, grows in much colder mountainous regions...
Cowley - Roscoea ganeshensis Cowley & W.J.Baker
- Roscoea humeanaRoscoea humeanaRoscoea humeana is a perennial herbaceous plant occurring in the Sichuan and Yunnan provinces of China. Most members of the ginger family , to which it belongs, are tropical, but R. humeana, like other species of Roscoea, grows in much colder mountainous regions...
Balf.f. & W.W.Sm. - Roscoea kunmingensisRoscoea kunmingensisRoscoea kunmingensis is a perennial herbaceous plant native to the mountains of China, being found in Yunnan. Most members of the ginger family , to which it belongs, are tropical, but R...
S.Q.Tong - Roscoea nepalensis Cowley
- Roscoea ngainoi A.A.Mao & Bhaumik
- Roscoea praecoxRoscoea praecoxRoscoea praecox is a perennial herbaceous plant occurring in the Yunnan province of China. Most members of the ginger family , to which it belongs, are tropical, but R. praecox, like other species of Roscoea, grows in much colder mountainous regions...
K.Schum. - Roscoea purpureaRoscoea purpureaRoscoea purpurea is a perennial herbaceous plant occurring in the Himalayas, particularly Nepal. Most members of the ginger family , to which it belongs, are tropical, but species of Roscoea grow in much colder mountainous regions...
Sm. - Roscoea schneideriana (Loes.) Cowley
- Roscoea scillifolia (Gagnep.) Cowley
- Roscoea tibeticaRoscoea tibeticaRoscoea tibetica is a perennial herbaceous plant native to the mountains of China, being found in Tibet, Sichuan and Yunnan. The species formerly included plants found in Bhutan; in 2000, these were separated into a new species, Roscoea bhutanica. Most members of the ginger family , to which it...
Batalin - Roscoea tumjensisRoscoea tumjensisRoscoea tumjensis is a perennial herbaceous plant occurring in the Himalayas, in Nepal. Most members of the ginger family , to which it belongs, are tropical, but R...
Cowley - Roscoea wardii Cowley
The hybrid R. auriculata × R. cautleyoides has occurred in cultivation, and has been given the name R. × beesiana Cowley & C.Whitehouse.
Cultivation
Some Roscoea species and cultivars are grown in rock gardens. They generally require moisture-retaining but well-drained soil and a position which receives sun for only part of the day. In cultivation they do not appear above ground until late spring or even early summer, thus escaping frost damage in regions where subzero temperatures occur. They then flower throughout summer into early autumn.They can be propagated by careful division of the individual growth points produced by a large plant, or by seed. Seed should not be allowed to dry out. If sown immediately it is ripe, it will normally germinate in the following summer. Young plants should be potted on before the tuberous roots become too intertwined.