Impatiens capensis Meerb. (the type specimen was mis-named, as it was thought by Meerburgh to have originated in South Africa (Burtt 1938)) has the smallest distribution of the three neophyte Impatiens species found in the wild. It is considered by Hultén & Fries (1986) to be a synonym of I. noli-tangere subsp. biflora [Walt.] Hult. in England and France.
Common names: Orange Balsam, Jewelweed, Lady’s earrings, Spotted Touch-me-not.
Synonym: I. biflora Walt.
Hybrids: None known in Europe. However, for the U. S. Pacific Northwest, Zika (2006) records hybrid Impatiens pacifica Zika - a cross between I. capensis and the local rare endemic I. ecalcarata.
Chromosome No.: 2n = 14 (Stace 2010); 2n = 20 (Clapham et al. 1987).
Photography: P. Day.
Mature leaves: 7-10 teeth with shortly decurrent base. Stems: hollow, succulent, translucent and branching to third order in mature plants.
Photography: P. Day.
Occurs in much of lowland England and eastern South Wales, where it has colonised the banks of many streams and rivers and has followed the canal network - its explosive capsule dehiscence and positive seed bouyancy aiding its hydrochorous dispersal (Trewick & Wade 1986). Maximum recorded altitude is 167 m near Wetton, mid-channel on the River Manifold in the Peak District National Park (v.c. 39) (J. Hawksford, pers. comm.).
It is a well established annual, usually found in small stands on marshy ground next to slow-moving water, often growing amongst coarse herbs in both open and shaded sites. It germinates from what can be a persistent seed bank (Perglová et al. 2009) from early March to mid-April, and flowers from early August to late September. A typical plant has both cleistogamous (closed and self-pollinated) and protandrous chasmogamous flowers, and is pollinated by bees, hoverflies and wasps. In eastern North America, an important pollinator is also the Ruby-throated Hummingbird. Rodwell (1991-2000) defines it as a component of W5 Alnus glutinosa woodland and S24 Phragmites australis tall-herb fen. However, in the Thames Valley it is commonly found within S14 Sparganium erectum swamp along riverbanks; OV32 Myosotis scorpioides communities in the dryer zones of fluctuating streams and associated ponds; and W6 Alnus glutinosa woodland along the upper reaches of Chilterns chalk streams. It has also been recorded in Shropshire in W6 and OV32.
Origin: neophyte from eastern North America. Thought to have escaped from cultivation in Surrey, and first noticed in 1822 by the R. Tillingbourne at Aldbury; with the first published record in 1829 on the R. Wey at Guildford (Louseley 1976). The species is now also naturalised in Denmark, Finland, France, Germany, the Netherlands and Poland.
Rarity: common and widespread.
Threat: none; however, it continues gradually to increase its spread. Change Index (New Atlas) of +0.71.
Conservation: a non-axiophyte. It is a naturalised invasive species which has no conservation value within the British flora. The plant is designated as having little or no economic or ecological impact by the Environment Agency and UK Water Framework Directive.
Little has been published in Britain with respect to the ecology of I. capensis - the only known account is by Bennett (1873). However, Maps Scheme records show a gradual extension northwards in range since the 1960s; and climate change might not only facilitate further extension of both the present altitude and northern latitude limits of the plant, but also modification to its currently relatively benign status. Regular monitoring of the plant’s status would be a worthwhile task. I would be very interested to learn if anyone has had experience of germination and seedling growth experiments for the species, particularly as seed stratification timing seems so difficult to judge with any accuracy. The Balsam Carpet (Xanthorhöe biriviata) moth is known to be phytophagous on I. capensis. Has anyone any knowledge of other fauna so inclined?
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- Bennett, A. W. 1872. On the Floral Structure of Impatiens fulva, Nuttall, with especial reference to the Imperfect Self-fertilized Flowers, Botanical Journal of the Linnean Society, 13, 147-153.
- Burtt, B. L. 1938. Bulletin of Miscellaneous Information (Royal Botanic Gardens, Kew), 1938 (4), 161-163.
- Lousley, J. E. 1976. Flora of Surrey. Newton Abbott, Devon: David & Charles.
- Perglová, I., Pergl, J., Skálová, H., Moracová, L., Jarošík, V. & Pyšek, P. 2009. Differences in germination and seedling establishment of alien and native Impatiens species, Preslia, 81, 357-375.
- Trewick, S. & Wade, P.M. 1986. The distribution and dispersal of two alien species of Impatiens waterway weeds in the British Isles. In: Proceedings of the International European Weed Research Society/Association of Applied Biologists 7th Symposium on Aquatic Weeds. Loughborough, 351-356.
- Zika, P. F. 2006. Impatiens pacifica (Balsaminaceae), a new hybrid jewelweed from the Pacific Northwest coast of North America, Novon, 16, 443-448.