Roscoea purpurea
Encyclopedia
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.
native to the Himalayas, and in particular Nepal
.
Like all members of the genus Roscoea, it dies back each year to a short vertical rhizome
, to which are attached the tuberous roots
. When growth begins again, "pseudostems" are produced: structures which resemble stems but are actually formed from the tightly wrapped bases (sheaths) of its leaves. R. purpurea can grow to over 50 cm tall, with wide leaves and a stout pseudostem, although the height varies. The leaf sheaths are pale green or may have a dark reddish-purple tinge.
The stem (peduncle
) of the flower spike is hidden by the leaf sheaths. The flowers are the largest of any species in the genus. They are usually purple to mauve in colour, although white- and red-flowered forms have been found in Nepal.
Each flower has the typical structure for Roscoea
(see the diagrams in that article). There is a tube-shaped outer calyx. Next the three petal
s (the corolla) form a tube slightly longer than the calyx, terminating in three lobes, an upright hooded central lobe and two slightly smaller side lobes. Inside the petals are structures formed from four sterile stamen
s (staminodes): two lateral staminodes form what appear to be small upright petals; two central staminodes are partially fused at the base to form a lip or labellum.
in 1806; it is the type species of the genus. The generic name honours Smith's friend William Roscoe
, the founder of the Liverpool Botanic Garden (now relocated to the Wavertree Botanic Gardens). The specific epithet refers to the colour of the flowers.
.
Species of Roscoea divide into two clear groups, a Himalayan clade and a "Chinese" clade (which includes some species from outside China). 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. R. purpurea falls into the Himalayan clade as would be expected from its distribution.
, R. purpurea emerges from the ground only in June, flowering from late July to early September. It requires shade for part of the day.
A red-flowered form found in Nepal has been named R. purpurea 'Red Gurkha'. Red is a colour not otherwise found in the genus.
For propagation, see Roscoea: Cultivation.
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...
occurring in the Himalayas, particularly Nepal
Nepal
Nepal , officially the Federal Democratic Republic of Nepal, is a landlocked sovereign state located in South Asia. It is located in the Himalayas and bordered to the north by the People's Republic of China, and to the south, east, and west by the Republic of India...
. Most members of the ginger family (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...
), to which it belongs, are tropical, but species of Roscoea
Roscoea
Roscoea is a genus of perennial plants of the family Zingiberaceae . 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...
grow in much colder mountainous regions. It is sometimes grown as an ornamental plant in gardens.
Description
Roscoea purpurea is a perennial herbaceous plantHerbaceous 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...
native to the Himalayas, and in particular Nepal
Nepal
Nepal , officially the Federal Democratic Republic of Nepal, is a landlocked sovereign state located in South Asia. It is located in the Himalayas and bordered to the north by the People's Republic of China, and to the south, east, and west by the Republic of India...
.
Like all members of the genus Roscoea, it dies 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 are attached 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...
. When growth begins again, "pseudostems" are produced: structures which resemble stems but are actually formed from the tightly wrapped bases (sheaths) of its leaves. R. purpurea can grow to over 50 cm tall, with wide leaves and a stout pseudostem, although the height varies. The leaf sheaths are pale green or may have a dark reddish-purple tinge.
The stem (peduncle
Peduncle (botany)
In botany, a peduncle is a stem supporting an inflorescence, or after fecundation, an infructescence.The peduncle is a stem, usually green and without leaves, though sometimes colored or supporting small leaves...
) of the flower spike is hidden by the leaf sheaths. The flowers are the largest of any species in the genus. They are usually purple to mauve in colour, although white- and red-flowered forms have been found in Nepal.
Each flower has the typical structure for Roscoea
Roscoea
Roscoea is a genus of perennial plants of the family Zingiberaceae . 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...
(see the diagrams in that article). There is a tube-shaped outer calyx. Next the three petal
Petal
Petals are modified leaves that surround the reproductive parts of flowers. They often are brightly colored or unusually shaped to attract pollinators. Together, all of the petals of a flower are called a corolla. Petals are usually accompanied by another set of special leaves called sepals lying...
s (the corolla) form a tube slightly longer than the calyx, terminating in three lobes, an upright hooded central lobe and two slightly smaller side lobes. Inside the petals are structures formed from four sterile stamen
Stamen
The stamen is the pollen producing reproductive organ of a flower...
s (staminodes): two lateral staminodes form what appear to be small upright petals; two central staminodes are partially fused at the base to form a lip or labellum.
Taxonomy
Roscoea purpurea 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; it is the type species of the genus. The generic 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). The specific epithet refers to the colour of the flowers.
Evolution and phylogeny
The Zingiberaceae family is mainly tropical in distribution. The unusual mountainous distribution of Roscoea 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 platesPlate tectonics
Plate tectonics is a scientific theory that describes the large scale motions of Earth's lithosphere...
.
Species of Roscoea divide into two clear groups, a Himalayan clade and a "Chinese" clade (which includes some species from outside China). 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. R. purpurea falls into the Himalayan clade as would be expected from its distribution.
Cultivation
Some Roscoea species and cultivars, including R. purpurea, are grown in rock gardens. They generally require a relatively sunny position with moisture-retaining but well-drained soil. As they do not appear above ground until late spring or even early summer, they escape frost damage in regions where subzero temperatures occur. When grown at Royal Botanic Gardens, KewRoyal Botanic Gardens, Kew
The Royal Botanic Gardens, Kew, usually referred to as Kew Gardens, is 121 hectares of gardens and botanical glasshouses between Richmond and Kew in southwest London, England. "The Royal Botanic Gardens, Kew" and the brand name "Kew" are also used as umbrella terms for the institution that runs...
, R. purpurea emerges from the ground only in June, flowering from late July to early September. It requires shade for part of the day.
A red-flowered form found in Nepal has been named R. purpurea 'Red Gurkha'. Red is a colour not otherwise found in the genus.
For propagation, see Roscoea: Cultivation.