Roscoea

Roscoea is a genus of perennial plants 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. 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 become like petals. Some species are grown as ornamental plants in gardens. 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. 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. 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). The relative number of bladeless versus complete leaves is one distinguishing feature of the two clades into which the genus is divided. 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. Like other members of the ginger family (Zingiberaceae), Roscoea flowers have a complex structure (superficially resembling that of an orchid, 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. 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. 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. 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. Roscoea was named by the English botanist James Edward Smith in 1806. The type species is R. purpurea. The name honours Smith's friend William Roscoe, the founder of the Liverpool Botanic Garden (remnants of which can now be found at Croxteth Hall). Roscoe is known to have been interested in 'gingers' (Zingiberales) and to have grown a number of collections of this group of plants. A 2002 classification of the Zingiberaceae family, 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. The Zingiberaceae 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.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).