Roscoea

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Roscoea
Roscoea purpurea 20070810-1338-183 trimmed.jpg
R. auriculata
Scientific classification OOjs UI icon edit-ltr.svg
Kingdom: Plantae
Clade: Tracheophytes
Clade: Angiosperms
Clade: Monocots
Clade: Commelinids
Order: Zingiberales
Family: Zingiberaceae
Genus: Roscoea
Sm. [1]
Species

See text.

Roscoea is a genus of perennial plants of the family Zingiberaceae (the ginger family). While most members of the ginger family are tropical, Roscoea species are native to cooler mountainous regions of the Himalayas, China and its southern neighbours. Roscoea flowers superficially resemble orchids, although they are not related. The flowers of Roscoea have a complicated structure, in which some of the showy coloured parts are not formed by petals, but by staminodes, sterile stamens which have evolved to resemble petals. Some species are grown as ornamental plants in gardens.

Contents

Description

Roscoea is found from Kashmir through the Himalayas to Vietnam, extending northwards into China. There are up to 22 recognized species, of which 8 are endemic to China. [1] [2] Typically they grow in grassland, in screes or on the edges of deciduous woodland at heights of 1,200–5,000 metres (3,900–16,400 ft), coming into growth at the start of the monsoon season. [3]

Species of Roscoea are small perennial herbaceous plants. 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). [2] The relative number of bladeless versus complete leaves is one distinguishing feature of the two clades into which the genus is divided. [4]

The flowers are borne in a spike at the end of the pseudostems. The stalk (peduncle) bearing the flowers may be long, so that the flowers appear well above the leaves, or short, so that they appear between the upper leaf sheaths. [5] Like other members of the ginger family (Zingiberaceae), Roscoea flowers have a complex structure (superficially resembling that of an orchid, [6] although they are not related). 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 stamens (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. [2] [Note 1]

Flower of Roscoea cautleyoides showing the petals and staminodes Roscoea cautleoides flower labelled.jpg
Flower of Roscoea cautleyoides showing the petals and staminodes

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. [2] [7]

Flower of Roscoea auriculata showing the "spurs" on the stamen Roscoea auriculata flower closeup.jpg
Flower of Roscoea auriculata showing the "spurs" on the stamen

Flower structure and pollination

The orchid-like flowers with a long floral tube appear to be an adaptation for pollination by long-tongued insects specializing in this type of flower. [8] 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. [9] 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. [10] 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. [8] 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. [10]

Taxonomy

Roscoea was named by the English botanist James Edward Smith in 1806. The type species is R. purpurea . [1] The name honours Smith's friend William Roscoe, the founder of the Liverpool Botanic Garden [11] (remnants of which can now be found at Croxteth Hall). [12] Roscoe is known to have been interested in "gingers" (Zingiberales) and to have grown a number of collections of this group of plants. [13]

Evolution and phylogeny

A 2002 classification of the family Zingiberaceae, based on molecular phylogenetic analysis, placed Roscoea in the tribe Zingibereae, subfamily Zingiberoideae. It was most closely related to the genus Cautleya , and then to Rhynchanthus , Pommereschea and Hedychium . [14] The family is mainly tropical in distribution. The unusual mountainous distribution of Roscoea and the closely related Cautleya may have evolved relatively recently as 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. [4] 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, R. australis ). [4]

Himalayan clade
Chinese clade
Distribution of Roscoea according to Ngamriabsakul, Newman & Cronk (2000); Himalayan clade shown in blue, Chinese clade shown in red. Black circle marks the distribution of R. ngainoi, discovered later. Roscoea distribution physical.png
Distribution of Roscoea according to Ngamriabsakul, Newman & Cronk (2000); Himalayan clade shown in blue, Chinese clade shown in red. Black circle marks the distribution of R. ngainoi , discovered later.

The two clades correspond to a geographical separation, the main distributions being divided by the section of the Brahmaputra River which flows south at the end of the Himalayan mountain chain. A historical biogeography study revealed that the evolutionary split between Cautleya and Roscoea occurred during the middle and late Eocene to the early Oligocene, coinciding with the proposed early uplift of the Himalayas and Qinghai–Tibetan Plateau. [16] Roscoea species were then divided into two distinct clades, simultaneous with the rapid extrusion of Indochina and accompanied by another Himalayan uplift around the Oligocene/Miocene boundary. [16] 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, [4] supported by biogeographic reconstruction. [16] Three species have an isolated distribution. R. brandisii , a member of the Himalayan clade, occurs to the south of the rest of the clade in the Khasia Hills in the modern Indian state of Meghalaya (formerly part of the state of Assam). R. australis, a member of the Chinese clade, occurs even further south, in the Chin Hills of Burma. [17] R. ngainoi , discovered after the phylogenetic analysis discussed above, is found roughly in an area in-between these two species, in the Indian state of Manipur. [15]

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. [18] 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). [4]

Species

As of August 2024, the Plants of the World Online accepts the following species of Roscoea: [1]

The hybrid R. auriculata × R. cautleyoides has occurred in cultivation, and has been given the name R. × beesiana Cowley & C.Whitehouse. [1]

Cultivation

Roscoeas in cultivation Roscoeas in cultivation 120819.jpg
Roscoeas in cultivation

Some Roscoea species and cultivars are grown in gardens, particularly rock gardens, as ornamental plants. Coming from monsoon regions, they require moisture in the summer but relatively dry conditions in winter. A moisture-retaining but well-drained soil is recommended, with a mulch of a material such as bark. They vary in their tolerance of sun exposure, most requiring shade for at least part of the day. In a Royal Horticultural Society trial, R. ganeshensis and R. purpurea f. rubra were the most harmed by excessive sunlight; R. cautleyoides , R. × beesiana and R. scillifolia the most resistant. In cultivation they do not appear above ground until late spring or even early summer; thus if planted deeply enough, up to 15 cm (6 in), they escape frost damage in regions where subzero temperatures occur. Different species and cultivars then flower throughout late spring and summer into early autumn. [3] [5]

They can be propagated by careful division in the autumn of the individual growth points produced by a large plant, or by seed. Seed should not be allowed to dry out. If sown immediately upon ripening, it will normally germinate in the following summer. Young plants should be potted on before the tuberous roots become too intertwined. [3] [5]

RHS trial

From 2009 to 2011, the Royal Horticultural Society held a trial involving around 100 entries submitted by British and other European sources. All proved hardy (rating H4, i.e. hardy anywhere in the British Isles). The Award of Garden Merit was given to 17 entries: [5]

Notes

  1. ↑ Some sources use the term "staminode" only for the lateral staminodes. See e.g. Wilford (2012 , p. 79).

Related Research Articles

<i>Cautleya</i> Genus of flowering plants

Cautleya is a small genus of perennial plants of the family Zingiberaceae, found in the eastern Himalayas through to China and Vietnam. It consists of two species of high-altitude tropical and temperate plants, native to cool forest areas – an unusual habitat for members of the Zingiberaceae. They are grown as ornamental flowering plants.

<i>Roscoea auriculata</i> Species of plant

Roscoea auriculata is a perennial herbaceous plant occurring in the eastern Himalayas, in Tibet, Bhutan, Nepal and Sikkim. Most members of the ginger family (Zingiberaceae), to which it belongs, are tropical, but R. auriculata, like other species of Roscoea, grows in much colder mountainous regions. It is sometimes grown as an ornamental plant in gardens.

<i>Roscoea cautleyoides</i> Species of flowering plant

Roscoea 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 (Zingiberaceae), to which it belongs, are tropical, but R. cautleyoides, like other species of Roscoea, grows in much colder mountainous regions. It is sometimes grown as an ornamental plant in gardens.

<i>Roscoea humeana</i> Species of plant

Roscoea humeana is a species of flowering plant in the family Zingiberaceae. It is a perennial 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. It is also grown as an ornamental plant in gardens.

<i>Roscoea purpurea</i> Species of flowering plant

Roscoea purpurea is a perennial herbaceous plant occurring in the Himalayas, particularly Nepal. Most members of the ginger family (Zingiberaceae), to which it belongs, are tropical, but species of Roscoea grow in much colder mountainous regions. It is sometimes grown as an ornamental plant in gardens.

<i>Roscoea alpina</i> Species of plant

Roscoea alpina is a perennial herbaceous plant native to the Himalayas. Most members of the ginger family (Zingiberaceae), to which it belongs, are tropical, but R. alpina, like other species of Roscoea, grows in much colder mountainous regions. It is sometimes grown as an ornamental plant in gardens.

<i>Roscoea tibetica</i> Species of flowering plant

Roscoea 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 (Zingiberaceae), to which it belongs, are tropical, but R. tibetica, like other species of Roscoea, grows in much colder mountainous regions. R. tibetica is sometimes grown as an ornamental plant in gardens. In 2020, it was proposed that R. tibetica be split again.

<i>Roscoea capitata</i> Species of flowering plant

Roscoea capitata is a perennial herbaceous plant native to the Himalayas, being found in Nepal. Most members of the ginger family (Zingiberaceae), to which it belongs, are tropical, but R. capitata, like other species of Roscoea, grows in much colder mountainous regions.

<i>Roscoea forrestii</i> Species of flowering plant

Roscoea forrestii is a perennial herbaceous plant occurring in the Sichuan and Yunnan provinces of China. Most members of the ginger family (Zingiberaceae), to which it belongs, are tropical, but R. forrestii, like other species of Roscoea, grows in much colder mountainous regions. It is sometimes grown as an ornamental plant in gardens. It was named after George Forrest (1873–1932) who discovered it in Yunnan.

<i>Roscoea tumjensis</i> Species of flowering plant

Roscoea tumjensis is a perennial herbaceous plant occurring in the Himalayas, in Nepal. Most members of the ginger family (Zingiberaceae), to which it belongs, are tropical, but R. tumjensis, like other species of Roscoea, grows in much colder mountainous regions.

<i>Roscoea praecox</i> Species of flowering plant

Roscoea praecox is a perennial herbaceous plant occurring in the Yunnan province of China. Most members of the ginger family (Zingiberaceae), to which it belongs, are tropical, but R. praecox, like other species of Roscoea, grows in much colder mountainous regions. It is sometimes grown as an ornamental plant in gardens.

<i>Roscoea bhutanica</i> Species of flowering plant

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 (Zingiberaceae), to which it belongs, are tropical, but R. bhutanica, like other species of Roscoea, grows in much colder mountainous regions.

Roscoea brandisii is a species of herbaceous flowering plant in the Zingiberaceae family. It is a perennial found in the state of Meghalaya, India. Most members of the ginger family, to which it belongs, are tropical, but R. brandisii, like other species of Roscoea, grows in much colder mountainous regions.

<i>Roscoea schneideriana</i> Species of flowering plant

Roscoea schneideriana is a perennial herbaceous plant found in China, in Tibet, Sichuan and Yunnan. Most members of the ginger family (Zingiberaceae), to which it belongs, are tropical, but R. schneideriana, like other species of Roscoea, grows in much colder mountainous regions.

<i>Roscoea ngainoi</i> Species of flowering plant

Roscoea ngainoi is a perennial herbaceous plant occurring in the Ukhrul district of Manipur state, India. Most members of the ginger family (Zingiberaceae), to which it belongs, are tropical, but like other species of Roscoea, R. ngainoi grows in much colder mountainous regions.

Roscoea ganeshensis is a perennial herbaceous plant occurring in Ganesh Himal in central Nepal. Most members of the ginger family (Zingiberaceae), to which it belongs, are tropical, but like other species of Roscoea, R. ganeshensis grows in much colder mountainous regions. It is used as an ornamental garden plant, requiring moisture and shade in the summer.

<i>Roscoea <span style="font-style:normal;">×</span> beesiana</i> Species of flowering plant

Roscoea × beesiana is considered to be a hybrid between R. auriculata and R. cautleyoides which occurred in cultivation. The flowers are variable: most forms have a pale cream base colour with varying amounts of purple streaking, particularly on the lip or labellum from midsummer to early autumn. It was given the Award of Garden Merit by the Royal Horticultural Society in 2011. It is classified as being hardy throughout the British Isles.

<i>Roscoea wardii</i> Species of flowering plant

Roscoea wardii is a perennial herbaceous plant occurring from eastern Arunachal Pradesh in India to western Yunnan in China. Most members of the ginger family (Zingiberaceae), to which it belongs, are tropical, but like other species of Roscoea, R. wardii grows in much colder mountainous regions.

<i>Roscoea scillifolia</i> Species of flowering plant

Roscoea scillifolia is a perennial herbaceous plant occurring in Yunnan in China. Most members of the ginger family (Zingiberaceae), to which it belongs, are tropical, but like other species of Roscoea, R. scillifolia grows in much colder mountainous regions. As of 2013, the species is only known in cultivation and may be extinct in the wild.

<i>Cautleya gracilis</i> Species of flowering plant

Cautleya gracilis is a perennial herbaceous plant in the family Zingiberaceae. It is found in the Himalayas through to south China and Vietnam. It is cultivated as an ornamental garden plant, hardy to a few degrees of frost.

References

  1. 1 2 3 4 5 WCSP (2011), World Checklist of Selected Plant Families, Royal Botanic Gardens, Kew , retrieved 2011-10-01, search for "Roscoea"
  2. 1 2 3 4 Wu, Delin; Larsen, Kai, Roscoea , retrieved 2011-10-01, in Wu, Zhengyi; Raven, Peter H. & Hong, Deyuan, eds. (1994), Flora of China, Beijing; St. Louis: Science Press; Missouri Botanical Garden, retrieved 2011-10-01
  3. 1 2 3 Wilford, Richard (1999), "Roscoeas for the rock garden", Quarterly Bulletin of the Alpine Garden Society, 67 (1): 93–101
  4. 1 2 3 4 5 Ngamriabsakul, C.; Newman, M.F. & Cronk, Q.C.B. (2000), "Phylogeny and disjunction in Roscoea (Zingiberaceae )" (PDF), Edinburgh Journal of Botany, 57 (1): 39–61, doi:10.1017/s0960428600000032 , retrieved 2011-10-03
  5. 1 2 3 4 Wilford, Richard (2012), "Roscoea on trial", The Plantsman, New Series, 11 (2): 78–85
  6. ↑ Botanica: The Illustrated A-Z of Over 10,000 Garden Plants and How to Cultivate Them, Köln: Könemann, 2004, ISBN   978-3-8331-1253-9 , p. 801
  7. ↑ Wu, Delin; Larsen, Kai, Zingiberaceae , retrieved 2011-10-01, in Wu, Raven & Hong 1994
  8. 1 2 Zhang, Zhi-Qiang & Li, Qing-Jun (2008), "Autonomous Selfing Provides Reproductive Assurance in an Alpine Ginger Roscoea schneideriana (Zingiberaceae)", Annals of Botany, 102 (4): 531–538, doi:10.1093/aob/mcn136, PMC   2701783 , PMID   18682439
  9. ↑ Ngamriabsakul, C. (2005), "Morphological study of the versatile anther group in the tribe Zingibereae (Zingiberaceae)" (PDF), Walailak Journal of Science and Technology, 2: 11–12, archived from the original (PDF) on 2012-06-12, retrieved 2011-10-22, p. 18
  10. 1 2 Zhang, Z.-Q.; Kress, W.J.; Xie, W.-J.; Ren, P.-Y.; Gao, J.-Y. & Li, Q.-J. (2011), "Reproductive biology of two Himalayan alpine gingers (Roscoea spp., Zingiberaceae) in China: pollination syndrome and compensatory floral mechanisms", Plant Biology, 13 (4): 582–589, Bibcode:2011PlBio..13..582Z, doi:10.1111/j.1438-8677.2010.00423.x, PMID   21668599
  11. ↑ Hyam, R. & Pankhurst, R.J. (1995), Plants and their names : a concise dictionary, Oxford: Oxford University Press, ISBN   978-0-19-866189-4 , p. 435
  12. ↑ Collard, Ian (2016). "50. Croxteth Hall". Liverpool in 50 buildings. Stroud. ISBN   978-1-4456-5895-7. OCLC   953223962.{{cite book}}: CS1 maint: location missing publisher (link)
  13. ↑ Cowley 1982, p. 748
  14. ↑ Kress, W. John; Prince, Linda M. & Williams, Kyle J. (2002), "The phylogeny and a new classification of the gingers (Zingiberaceae): evidence from molecular data", American Journal of Botany, 89 (10): 1682–1696, doi:10.3732/ajb.89.10.1682, PMID   21665595
  15. 1 2 Mao, A. A. & Bhaumik, M. (2007), "Roscoea ngainoi (Zingiberaceae) sp. nov. from Manipur, India", Nordic Journal of Botany, 25 (5–6) (published 2008): 299–302, doi:10.1111/j.0107-055X.2008.00186.x
  16. 1 2 3 Zhao, Jian-Li; Xia, Yong-Mei; Cannon, Charles H.; Kress, W. John; Li, Qing-Jun (2016). "Evolutionary diversification of alpine ginger reflects the early uplift of the Himalayan–Tibetan Plateau and rapid extrusion of Indochina". Gondwana Research. 32: 232–241. Bibcode:2016GondR..32..232Z. doi: 10.1016/j.gr.2015.02.004 .
  17. ↑ Cowley 1982
  18. ↑ Ngamriabsakul, C. & Newman, M.F. (2000), "A New Species of Roscoea Sm. (Zingiberaceae) from Bhutan and Southern Tibet" (PDF), Edinburgh Journal of Botany, 57 (2): 271–278, doi:10.1017/s0960428600000202, archived from the original (PDF) on 2012-06-12, retrieved 2011-10-04

Bibliography

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