Impatiens edgeworthii in the EPPO region: addition to the EPPO Alert List
Impatiens edgeworthii (Balsaminaceae) is an annual species native to the Western Himalayas and currently has a limited distribution in the EPPO region. The species is present in the wild in Germany where it has shown invasive behaviour in forests in Central Germany. Due to the invasive nature of this species in the area described, I. edgeworthii can be considered an emerging invader within the EPPO region.
Impatiens edgeworthii is native to the Western Himalayas where the species is found in high altitude valleys in India, Nepal and Pakistan.
EPPO region: Germany.
Asia: India (Himachal Pradesh), Nepal, Pakistan.
Impatiens edgeworthii as an annual herb which is recorded to grow between 25-60 cm tall in its native range. The stem is erect and branched and leaves are approximately 40-180 x 15-75 mm, elliptic-ovate. Petioles are 15-50 mm long. Flowers are yellow with red streaks in the throat, 25-36 mm long. Morgan (2007) details that there is also a pale lilac flower variety. Capsules are 20-30 mm in length, linear and erect. Seeds are oblong in shape and approximately 3 mm in length. In Germany, the plant is recorded to grow taller compared to populations in the native range – up to up to 180 cm tall (Baade and Gutte, 2008). There is also more variation in flower colour from samples described by Baade and Gutte (2008), and by Weiss (2013). In Germany, the flower colour can vary from yellow, yellow-white, white and pale violet, where yellow and brown specks are seen in the throat of the flower for the violet and yellow coloured flowers, respectively, and the white flowered variety shows red to brown specks.
Biology and ecology
The genus Impatiens contains approximately 1 200 species of annual and perennial herbs mainly distributed in the montane areas of tropical and subtropical Asia and Africa. In the native range, I. edgeworthii flowers from July to September and the plant is killed by the first autumnal frosts. Seedlings, however, can survive several degrees below zero (Weiss, 2015). Germination requires a period of cold stratification and moisture, but not necessarily frost, as plants in Germany germinate normally after a winter without frost (Weiss, 2015). I. edgeworthii is a good source of nectar for pollinators, in particular for honey bees, bumblebees and Antophora spp. in the late summer and early autumn (Weiss, 2013).
In the native range I. edgeworthii occurs in damp shady montane habitats often growing along gullies and streams from 1800-3000m above sea level (a.s.l.). The plant can form dense stands along roadsides where the ground is irrigated by ditches. In Germany, I. edgeworthii occurs in similar damp shaded habitats (Weiss, 2013). The species has successfully invaded forests in Central Germany and is found to extend outwards along tracks and forest edges (Weiss, 2013). In undisturbed woodland, I. edgeworthii does not seem to be able to establish as it does in woodland areas where there has been some level of disturbance.
Natural dispersal is by seed. Seeds are encased in explosive seed pods, which upon ripening project seeds some distance from the paternal plant. When the plant grows near water ways, seeds are incorporated into the water body and transported downstream. Impatiens edgeworthii is traded as an ornamental species. As the species is an annual, the plant is traded by seed, mainly through mail order on the internet. As the species has an explosive seed mechanism, escape from gardens into the wild is a pathway for its spread.
In Germany I. edgeworthii is reported to outcompete its close relative – Impatiens parviflora. However, I. edgeworthii has not been shown to outcompete the native, I. noli-tangere (Weiss, 2013). I. edgeworthii has been shown to compete with the commonly occurring Urtica dioica L. Because of scarce information on its impacts, the plant is listed on the Grey List of potentially invasive species (Lauterbach and Nehring 2013). In Germany I. edgeworthii has been shown to change plant community structure in invaded woodlands (Weiss, 2013).
Any methods to control I. edgeworthii should be conducted before the plant sets seed. As with most annual Impatiens species, the root system is relatively shallow and therefore manual control, in the form of hand pulling can be effective to remove discrete populations of the plant. However, hand pulling should take place early in the season before the plant sets flowers/seed. Strimming or severing the stem is potentially effective with annual Impatiens species, though this must be conducted below the first node to prevent re-sprouting. Plants completely mown in June sprouted and flowered in September (Weiss, 2013).
Baade H, Gutte P (2008) Impatiens edgeworthii HOOK. F. – Ein Für Deutschland neues Springkraut. Braunschweiger Geobotanische Arbeiten 9, 55–63
Lauterbach D, Nehring S (2013) Naturschutzfachliche Invasivitätsbewertung Impatiens edgeworthii – Buntes Springkraut. BfN Skripten 352, 110-111
Morgan R (2007) Impatiens: The Vibrant World of Busy Lizzies, Balsams, and Touch-Me-Nots. Portland, USA. Timber Press.
Weiss V (2013) Zur Ökologie von Impatiens edgeworthii HOOK. F. in Mitteldeutschland. Mitteilungen zur floristischen Kartierung in Sachsen-Anhalt 18, 15–29.
Weiss V (2015) Die rote Pest aus grüner Sicht: Springkräuter – von Imkern geschätzt, von Naturschützern bekämpft. Stocker Verlag, Graz, Stuttgart, 160 pp.