Rubus ellipticus is commonly known as yellow Himalayan raspberry in Hawai'i where it is considered a weed or naturalized alien invasive plant although it was initially deliberately introduced in 1961. It is also listed as one of the 100 of the world's worst invasive alien species' in the Global Invasive Species Database (GISD) of the Invasive Species Specialist Group (ISSG).
R. ellipticus is a strong, thorny shrub able to form impenetrable thickets several meters wide and between 2.2 and 4.5 meters tall. Shrubs of this type from the genus Rubus are called brambles. It has hardy, perennial roots from which comparatively short-lived prickly stems grow each year. The stems produce a yellow fruit in their second year before dying off approximately two months after flowering; the flowers are small and white with five petals, with both male and female sex parts and are pollinated by insects.
The individual plant spreads through vigorous root growth while the species is spread through the numerous tiny seeds on consumed fruit being transported by fruit-eating birds or mammals, including humans. As it may be cultivated from cuttings of half-ripe wood it is possible it could spread from cleared plant parts being dumped in other areas. It grows at elevations starting at around 700m and up to as high as 2600m. It grows where there is an annual rainfall between 1250 and 7000 millimeters, from moderately moist (mesic) to considerably moist (hydric). Its habitat range is extensive, contributing to its invasiveness, being able to flourish in shrubberies and on open hillsides near water in its native Himalayas, in open canopy forests, the deep shade of rainforests and pastureland in Hawai'i as well as waste land (ruderal) and agricultural land, and particularly where land has been disturbed by feral pigs.
R. ellipticus is a native of south-east Asia, found in the Himalayas from Pakistan to Nepal to southern China, as well as Bhutan, Burma, India, Myanmar, Philippines, Sri Lanka and Thailand. It has been introduced to several places but is listed as invasive only in the Hawaiian Islands so far, having become established on Hawai'i and been found in several places on Maui. It has become established in some parts of the Andes mountain chain in South America where it may become a problem.
The Hawaiian Islands are volcanic and therefore hilly and mountainous in nature, providing habitats at elevations suitable to R. ellipticus. The near-constant trade winds from the northeast provide ample rainfall on the windward side of Hawai'i to suit the shrub although it might find the sheltered leeward side dryer than it likes. Frosts are rare under 1200m and it does have some ability to tolerate them. The islands are at a similar latitude to its native range.
Having risen from the sea, the islands' native flora will have been initially introduced by birds and as such be from limited founders. Competition and threats are likely to have been considerably less than for R. ellipticus evolving on a continent, so it is likely to be hardier and more competitive than local equivalents. For example, the native R. hawaiiensis has no prickles or thorns for protection from feral sheep, goats and pigs, while R. ellipticus is amply protected by such. Hawai'i is also a major holiday destination, trampers and hikers are likely to cause disturbance in park regions and spread seeds on boots that will help the shrub's development and dispersal.
Threat To Other Countries:
Yellow Himalayan raspberry could quite easily be introduced to other countries accidentally; its extensive native range in Asia and its establishment in a significant holiday destination like Hawai'i means that seeds might hitchhike on the boots, clothes or camping gear of travelers or tourists. It may be hoped that such occurrences would be detected by border security, such as detector dogs.
A scarier possibility is that a traveler may consume some fruit, they are sold in many places where they are native, just before journeying. They would pass through border controls with the seeds in their gastrointestinal tract. If they then happened to use a composting toilet, R. ellipticus might get its chance to establish itself. This is particularly feasible for travelers who are "wwoofers", as organic farms in many countries are quite likely to have composting toilets.
A further possibility is the deliberate introduction of the plant by smuggling in seeds or cuttings or more easily, deliberately eating the fruit prior to travel and extracting seeds from the feces after arrival. The fruit can be eaten and are said to be delicious or used to produce a dye, various parts of the plant can be used in natural remedies and the plants themselves can be planted to prevent soil erosion. There are bound to be some people that would see these as useful attributes and decide to introduce them to their home country without considering the possible consequences to native species. Unfortunately, it would probably only take one such person.
If, for example, it were introduced into New Zealand, it would have a very good chance of becoming invasive in the top half of the North Island, where the climate and topography would seem highly suitable to its needs. Many Kiwis enjoy the outdoor life, camping and tramping, and may unwittingly aid in its dispersal. Native and introduced frugivorous (fruit eating) birds are likely to find the fruit palatable, also helping it spread. Feral pigs in Northlands, tree-felling and agricultural practices are all likely to create abundant disturbed areas to facilitate its growth. Once established it is very hard to eradicate as they are finding in Hawai'i. Like other species of Rubus it is vulnerable to honey fungus but that is not currently extant in NZ, although it might slow the spread in other countries.
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