Description
Potentially Misidentified Species - Native Iris spp. have blue-purple flowers. I. pseudacorus is unmistakable when in bloom, since it is bright yellow (Brown and Brown 1984).
Taxonomy
| Kingdom | Phylum | Class | Order | Family | Genus |
|---|---|---|---|---|---|
| Plantae | Magnoliophyta | Liliopsida | Liliales | Iridaceae | Iris |
Synonyms
Invasion History
Chesapeake Bay Status
| First Record | Population | Range | Introduction | Residency | Source Region | Native Region | Vectors |
|---|---|---|---|---|---|---|---|
| 1915 | Established | Expanding | Introduced | Regular Resident | Europe | Eurasia | Ornamental(Garden Escape) |
History of Spread
Iris pseudacorus (Yellow Iris) is native from central Scandinavia south to Turkey and North Africa (Sutherland 1990). It was probably imported very early as an ornamental. It was cultivated in the Chesapeake Bay watershed before 1771, by Thomas Jefferson at Monticello (Charlottesville) VA (Wells and Brown 2000). While gardens may be the most frequent source of introductions, I. pseudacorus was included on a list of ballast plants for New York and Philadelphia (Torrey Botanical club 1888).
The earliest report of its 'wild' occurrence in North America, outside cultivation, that we've found was from the 'muddy banks of Delaware River; naturalized' (Tatnall 1860). It was found growing wild in the Hudson River Valley in 1868 (Mills et al. 1997). Its range was given as New England, NY, NJ by Robinson and Fernald (1908). It is now known from 40 states (Natural Resources Conservation Service 2001).
Iris pseudacorus has been introduced to the Great Lakes and Hudson River estuaries (Mills et al. 1993; Mills et al. 1997) and to the Sacramento-San Joaquin Delta (Thomas 1980; Cohen and Carlton 1995). It is now found across the United States, but is absent in some plains and mountain states (Natural Resources Conservation Service 2001). It is also introduced in New Zealand (Sutherland 1990).
Iris pseudacorus is not listed in 19th century Baltimore or Washington D.C. floras or in Shreve et al.'s (1910) plant survey for MD. Herbarium specimens were collected from Dyke Marsh, Alexandria VA in 1915 (U. S. National Herbarium collections) and Hitchcock and Standley (1919) reported it as 'established along the Potomac marshes'. It is now found in the Potomac estuary from Roosevelt Island (Thomas 1980) to Caledon Natural Area, King George County, VA (Simmons et al. 1995), over a fresh to lower mesohaline gradient. Fernald (1941) found it near the York River above Yorktown VA.
Iris pseudacorus is also found in the upper Bay from Northeast River (Cecil County) (Garbisch and Coleman 1978) to North Point State Park, on Back River, just north of Baltimore (Fofonoff 1997 personal observation), where it was associated with mesohaline vegetation. It is not found in the Rhode River-South River area (Philipp and Brown. 1965; Higman 1968; Fofonoff 1995-1996 personal observation). Iris spp. were found in the Upper Bay as far south as Fairlee Creek (opposite Baltimore on Eastern Shore) and in the upper Choptank and Nanticoke Rivers (Sipple 1978). Iris pseudacorus was recently found growing in supratidal dune swales on Chincoteague Island (Sipple 1995).
History References - Fernald 1941; Garbisch and Coleman 1908; Higman 1968; Hitchcock and Standley 1919; Mills et al. 1993; Mills et al. 1997; Natural Resources Conservation Service 2001; Phillip et al. 1965; Robinson and Fernald 1908; Shreve et al. 1910; Sutherland 1990; Sipple 1978; Sipple 1995; Simmons et al. 1995; Tatnall 1860; Thomas 1980; Torrey Botanical Club 1888; Wells and Brown 2000
Invasion Comments
Ecology
Environmental Tolerances
| For Survival | For Reproduction | |||
|---|---|---|---|---|
| Minimum | Maximum | Minimum | Maximum | |
| Temperature (ºC) | -10.0 | |||
| Salinity (‰) | 0.0 | 10.0 | 0.0 | |
| Oxygen | hypoxic | |||
| pH | 2.0000000000 | 8.3700000000 | ||
| Salinity Range | fresh-meso |
Age and Growth
| Male | Female | |
|---|---|---|
| Minimum Adult Size (mm) | 400.0 | 400.0 |
| Typical Adult Size (mm) | 950.0 | 950.0 |
| Maximum Adult Size (mm) | 1500.0 | 1500.0 |
| Maximum Longevity (yrs) | 15.0 | 15.0 |
| Typical Longevity (yrs | 9.0 | 9.0 |
Reproduction
| Start | Peak | End | |
|---|---|---|---|
| Reproductive Season | |||
| Typical Number of Young Per Reproductive Event |
|||
| Sexuality Mode(s) | |||
| Mode(s) of Asexual Reproduction |
|||
| Fertilization Type(s) | |||
| More than One Reproduction Event per Year |
|||
| Reproductive Startegy | |||
| Egg/Seed Form |
Impacts
Economic Impacts in Chesapeake Bay
Iris pseudacorus (Yellow Iris) is widely cultivated in the Chesapeake Bay watershed. Its flowers are an attraction in wetland parks (Theodore Roosevelt Island; Kenilworth Aquatic Gardens; Dyke Marsh) in the Washington DC area (Fofonoff, personal observation).
Based on current information, effects of I. pseudacorus on habitat and wildlife appear to be localized to the upper tidal Potomac (Sipple 1995; Silberhorne 1995; Strong and Kelloff 1994, Thomas 1980). In marshes on Theodore Roosevelt Island, the major effect on human utilization of wildlife would be replacement of a major waterfowl food, Peltandra virginica (Arrow Arum) (Thomas 1980).
References- Fofonoff, personal observation; Sipple 1995; Silberhorne 1995; Strong and Kelloff 1994, Thomas 1980
Economic Impacts Outside of Chesapeake Bay
Apparently, few negative impacts of Iris pseudacorus (Yellow Iris) have been noted either in its native or introduced range, aside from the replacement of waterfowl food species noted on Theodore Roosevelt Island, Potomac River, by Thomas (1980). It is avoided by grazing livestock, and is apparently toxic, but Sutherland (1990) does not report adverse impacts on agriculture resulting from this. One reason may be that plants are frequently trampled and killed by high densities of livestock (Sutherland 1990).
References - Sutherland 1990; Thomas 1980
Ecological Impacts on Chesapeake Native Species
Ecological impacts of Iris pseudacorus (Yellow Iris) have been reported on Theodore Roosevelt Island in the upper tidal Potomac. In other regions of the Potomac and Upper Bay, I. pseudacorus does not seem to be abundant enough to have significant impacts (Mark Strong 1995; William Sipple 1995; Silberhorne 1996).
Competition - In tidal marshes on Theodore Roosevelt Island; I. pseudacorus prefers higher elevations and less inundation than native Peltandra virginica (Arrow Arum). Iris pseudacorus can replace native vegetation by creating a hardpan of packed rhizomes. Iris pseudacorus is favored by debris and disturbance, and so is likely to remain on the island in swamp transition areas. Its rhizomes prevent germination of Salix nigra (Black Willow) seedlings (Thomas 1980). Competition with native species of Iris seems likely, but is not documented.
Iris pseudacorus (Yellow Iris) is included on state invasive plant lists for MD (Cooley 1993), and VA (Virginia Department of Conservation and Recreation 1999).
Habitat Change - See 'Competition' above. Iris pseudacorus, by raising and covering the marsh surface, promotes the growth of Fraxinus pennsylvanicus (Green Ash) instead of Salix nigra. The latter requires bare mineral soil to germinate. The promotion of F. pennsylvanicus hastens the transition from marsh to swamp (Thomas 1980).
Toxic- 'Leaves and rhizomes contain glycosides that are not destroyed by drying or storage' (Sutherland 1990a). Iris pseudacorus causes gastroenteritis and diarrhea in sheep and cattle. It is nibbled but not eaten by muskrats and nutria (Sutherland 1990; Thomas 1980). It replaces more edible plants such as Peltandra virginica and Acorus spp. (Thomas 1980).
References - Silberhorne 1995; Sipple 1995; Strong 1995; Sutherland 1990; Thomas 1980
Ecological Impacts on Other Chesapeake Non-Native Species
Ecological impacts of Iris pseudacorus (Yellow Iris) have been reported on Theodore Roosevelt Island in the upper tidal Potomac. In other regions of the Potomac and Upper Bay, I. pseudacorus does not seem to be abundant enough to have significant impacts on introduced biota (Strong 1995; Sipple 1995; Silberhorne 1996).
Competition- On Theodore Roosevelt Island, I. pseudacorus' major introduced competitor is Acorus calamus (Calamus)*. Competitive interactions between A. calamus (Calamus) and Iris pseudacorus (Yellow Iris) were studied by Thomas (1980) in marshes on Theodore Roosevelt Island in the Potomac River. Acorus calamus is expected to succeed Iris in many areas of the marsh, but I. pseudacorus is favored by debris and disturbance, and so is likely to remain on the island in swamp transition area (Thomas 1980). Competition with other introduced plants in low-salinity regions of Chesapeake Bay, such as Murdannia keisak and Lythrum salicaria, is possible but not documented.
[*Thomas was apparently unaware of the distinction between A. calamus and A. americanus, but based on Thompson's (1993) survey of herbarium specimens, these plants were probably true A. calamus. ]
References- Strong 1995; Sipple 1995; Silberhorne 1996; Thomas 1980; Thompson 1993
References
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Garbisch, E. W., Jr.; Coleman, L. B. (1978) Tidal freshwater marsh establishment in upper Chesapeake Bay- Pontedaria cordata and Peltandra virginica., In: Good, R. E., Whigham, D. F., and Simpson, R. L.(Eds.) Freshwater Wetlands. , New York. Pp. 285-298
Gleason, Henry A. (1963) The new Britton and Brown illustrated flora of the northeastern United States and adjacent Canada, In: (Eds.) . , New York. Pp.
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Mills, Edward L.; Scheuerell, Mark D.; Carlton, James T.; Strayer, David (1997) Biological invasions in the Hudson River: an inventory and historical analysis., New York State Museum Circular 57: 1-51
1997-2024 USDA PLANTS Database.. Onine databse
Philipp, Charles C.; Brown, Russell C. (1965) Ecological studies of transition-zone vascular plants in South River, Maryland, Chesapeake Science 6: 73-81
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Simmons, Mark P.; Ware, Donna M.; Hayden, W. John (1995) The vascular flora of the Potomac River watershed of King George County, Virginia, Castanea 60: 179-209
1995 Introduced plants in Chesapeake Bay, letters and telephone conversations.
1995 Introduced plants in the Chesapeake Bay region, conversation with Paul Fofonoff.
Strong, Mark T.; Kelloff, Carol L. (1994) Intertidal vascular plants of Brent Marsh, Potomac River, Stafford County, Virginia, Castanea 59: 354-366
Sutherland, W. J.; Walton, D. (1990) The changes in morphology and demography of Iris pseudacorus L. at different heights on a salt marsh, Functional Ecology 4: 655-659
Sutherland, William J. (1990) Biological flora of the British Isles No. 169. Iris pseudacorus L., Journal of Ecology 78: 833-848
Tatnall, E. (1860) Catalogue of the phenogamous and filicoid plants of Newcastle County, Delaware., , Wilmington DE. Pp.
Thomas, Lindsey Kay (1980) The impact of three exotic plant species on a Potomac island., , Washington, D. C.. Pp.
Torrey Botanical Club (1888) Preliminary catalog of Anthophyta and Pteridophyta, reported as growing spontaneously within one hundred miles of New York City., , New York. Pp.