| Rheum rhabarbarum | |
|---|---|
 | |
Scientific classification | |
| Kingdom: | Plantae |
| Clade: | Tracheophytes |
| Clade: | Angiosperms |
| Clade: | Eudicots |
| Order: | Caryophyllales |
| Family: | Polygonaceae |
| Genus: | Rheum |
| Species: | R. rhabarbarum |
| Binomial name | |
| Rheum rhabarbarum | |
| Synonyms | |
Rheum rhabarbarum is aspecies offlowering plant in the familyPolygonaceae, native to a region stretching from southernSiberia to north and central China.[1] It has been harvested from the wild for centuries for its root, which was harvested for use as a popular medicine in Europe and Asia. It was later cultivated for its root in England and Russia. It is considered to be one of the species involved in the development of culinaryrhubarb, for which the scientific nameR. rhabarbarum is sometimes (erroneously) used.
Rheum rhabarbarum was first described byCarl Linnaeus in 1753.[3] Linnaeus also describedR. undulatum, but this is now considered to be the same species.[1]
The namerha barbarum,Latin for 'foreign rha', was first used in the writings ofCelsus, who uses the word to describe a valued medicinal root imported from the east.[4]
According to the 2003 key in theFlora of China, this species is distinguished from other entire-leavedrhubarbs in China with leaves having a wavy or crisped margin;R. wittrockii,R. webbianum,R. australe andR. hotaoense, by having less than 1 cm-sized fruit, yellow-white to greenish-white flowers, and the surface of the rachis ofpanicle covered inpapilla. In many characters it is most similar toR. webbianum, and somewhat less soR. hotaoense.[5]
There have been at least two studies investigating thekaryotypy of this species, both studies focussing on the synonymR. undulatum. Both 2n=22 and 2n=44 have been found. It is possible that this karyotypic diversity indicates the existence of one or morecryptic species, because thepolyploid forms would essentially be reproductively isolated.[6]
It is native to an area of southeasternSiberia in theDaurian region around and stretching east fromLake Baikal inRussia, and in northernMongolia.[7][8] In China, it occurs in the northern provinces ofHebei,[2][9]Heilongjiang,[2][9]Henan,[9]Hubei,[2][9]Jilin,[2][9]Inner Mongolia,[2][9]Shanxi[2][9] andShaanxi.[9]
In China, it is known as a species growing on mountain slopes at 1,000–1,600 m elevation.[2] In Russia it occurs in sandy ground along field edges, on the steppes, and in the regionally uncommon copses of woodland.[7]
In China, it flowers in June, and has fruit after July.[2]
Most documented insect relationships with this species are muddied by the misapplication of the nameR. rhabarbarum to plants ofR. ×hybridum. As such, most of the insects which are said to use this species as a food plant are generalists from Europe or North America which did not actually eat this species nor are native to the region where this species occurs. An exception is the butterflyLycaena violacea, whose caterpillars are only known to feed onR. rhabarbarum and whose range is concurrent with that of its host plant (mostLycaena spp. are specialised onPolygonaceae).Cosmia trapezina var.exigua is roughly native to some of the same areas, and its European variety has been found to have eaten rhubarb in Finland (it usually feeds on various tree species). Other species found to eat (garden) rhubarb which occur in the native range of this plant areArctia caja,Hydraecia micacea,Spilarctia luteum andXestia baja.[10]
Rheum rhabarbarum (syn.R. undulatum) was one of a number of distinct species grown in Europe before the beginning of the 18th century. Initially the roots of a related species, possiblyR. rhaponticum, were used for medicinal purposes. A putative hybrid of unknown origin,Rheum ×hybridum, was also grown. The three taxa were grown as vegetable crops in England and Scandinavia by the early 18th century. They readily hybridize, and culinaryrhubarb was developed by selecting open-pollinated seed, so that its precise origin is almost impossible to determine.[11] In appearance, culinary rhubarb varies continuously betweenR. rhabarbarum andR. rhaponticum. Modern rhubarb cultivars aretetraploids with 2n = 44, in contrast to 2n=22 for the wild species such asR. rhaponticum.[12]