You are here
Species
Polygonum
IUCN
NCBI
EOL Text
More info for the term: presence
Seeds of the 3 knotweeds may be dispersed by wind, birds, insects, or water. One review reports that the presence of a persistent, winged perianth and an abscission zone suggest wind-dispersal of Japanese knotweed seeds [11]. Giant knotweed seeds are wind-dispersed in its native range [129]. In Pennsylvania birds and insects consumed giant and Japanese knotweed seeds, which the author suggested may indicate potential dispersal mechanisms [87]. Near Washington, DC, Japanese knotweed seeds were washed downstream in floods [103]. In Belgium, the majority of Japanese knotweed seeds fell within the vicinity of the parent plant, though seedfall patterns indicated the potential for dispersal beyond 52 feet (16 m) for a small amount of seeds [126]. As of this writing (2010) no information was available regarding the dispersal of Bohemian knotweed seeds.
The genus name for knotweeds is Polygonum L. (Polygonaceae). This review summarizes information on the following knotweed taxa:
Polygonum sachalinense F. Schmidt ex Maxim., giant knotweed
Polygonum cuspidatum Siebold & Zucc., Japanese knotweed [67]
and their hybrid:
Polygonum × bohemicum (Chrtek & Chrtková) Zika &
Jacobson (cuspidatum × sachalinense), Bohemian knotweed [42,47]
In this review, species are referred to by their common names, and "3 knotweeds" refers to all 3 taxa.
Hybrids: Japanese and giant knotweed hybridize to form Bohemian knotweed. There is some concern that Bohemian knotweed may be more invasive than either of its parents due to its greater genetic diversity
([3], review by [46]), possibly allowing it to adapt to diverse
habitat conditions and establish in plant communities where giant or Japanese knotweed have not established (review by [46]). Bohemian knotweed also backcrosses
with giant and Japanese knotweed to produce viable seeds. This seed-producing ability is of
concern because the majority of reproduction of the 3 knotweeds is currently (2010) thought
to be vegetative [3] (see Regeneration Processes).
In Europe, Japanese knotweed also hybridizes with Bukhara fleeceflower (Polygonum baldschuanicum Regel). In the United States, hybrids morphologically similar to those
between Japanese knotweed and Bukhara fleeceflower have been grown from field-collected
seeds, but seedling establishment has not been observed in the wild (review by [104]).
Varieties: A dwarf variety of Japanese knotweed, Polygonum cuspidatum Siebold & Zucc. var. compactum (Hook f.)
Bailey, occurs in North America [67]. One source suggests that
this variety dominates Japanese knotweed populations in North America [46],
though mention of this variety was encountered infrequently in the literature.
Annual or perennial herbs, usually (in ours) prostrate. Ochreae present. Leaves small compared to Persicaria. Inflorescences all axillary, each with 6 or fewer flowers; bracts similar to the leaves. Perianth segments 4, petaloid, not enlarging in fruit. Stamens 8. Styles 3, free; nut 3-angled.
| License | http://creativecommons.org/licenses/by-nc/3.0/ |
| Rights holder/Author | Mark Hyde, Bart Wursten, Petra Ballings, Flora of Zimbabwe |
| Source | http://www.zimbabweflora.co.zw/speciesdata/genus.php?genus_id=515 |
More info for the terms: breeding system, dioecious, gynodioecious, monoecious, perfect
Pollination: The 3 knotweeds are insect-pollinated. In Pennsylvania they were pollinated by bees, ants, butterflies, and beetles [87]. Near Washington, DC, Japanese knotweed was pollinated by bees [103].
Breeding system: Reports of the breeding systems of the 3 knotweeds are conflicting. For a review of their breeding systems, see [46]. One review that considered plants and herbarium specimens from North America reports that Japanese knotweed is gynodioecious [7]. Another review reports that Japanese knotweed is functionally dioecious in the United States, while it is gynodioecious in the United Kingdom [87]. A third review describes the Japanese knotweed breeding system as "leaky" dioecious or subdioecious in North America because populations contain both male and female plants that maintain vestigial reproductive parts of the other sex [53]. A flora from the Pacific Northwest reports Japanese knotweed as generally monoecious [58]. Giant knotweed is reported as dioecious in the United States [58] or gynodioecious in the United Kingdom [3]. In Pennsylvania, the majority of plants from a population containing all 3 knotweeds had male-fertile and female-fertile flowers on separate plants and relatively few perfect flowers were found [87].
The sexual characteristics of a particular population have important implications for the viability of seeds. In Pennsylvania, viable seeds of the 3 knotweeds were not found when male-fertile plants were absent from the site, but many viable seeds were produced when both female and male-fertile plants were present [87]. In New Jersey, one researcher found Japanese knotweed populations of both sexes and other populations of just females; female-only populations produced seeds but they were not viable [74].
giant knotweed
Sakhalin knotweed
Japanese bamboo
Japanese knotweed
crimson beauty
Mexican bamboo
Japanese fleeceflower
Bohemian knotweed
Distribution: Giant knotweed has a discontinuous distribution in North America. In eastern North America, giant knotweed occurs from Tennessee and North Carolina north into eastern Canada. Some states in the Great Lakes region (e.g., Indiana) and New England (e.g., New Hampshire) lack giant knotweed. Giant knotweed is also found in Louisiana. In western North America, giant knotweed occurs from California north to Alaska, with populations also in Idaho and Montana.
Japanese knotweed is more widely distributed than giant knotweed. The Plants Database reports Japanese knotweed occurring in almost all of the United States with the exceptions of Florida, Alabama, Texas, New Mexico, Arizona, Wyoming, and North Dakota. However, one source documented Japanese knotweed in Arizona [39]. Japanese knotweed occurs throughout Canada, with the exceptions of Labrador, Saskatchewan, Alberta, Northwest Territories, and Yukon. Plants Database provides distribution maps of giant and Japanese knotweed.
As of this writing (2010), the distribution of Bohemian knotweed in North America is not well known. The Plants Database reports Bohemian knotweed occurring in British Columbia, Ontario, and Quebec (2010). However, sources included in this profile have also documented Bohemian knotweed in New York [97,107] and Washington [31,109,111,153]. It is likely that the distribution of all 3 knotweeds is expanding in the United States.
Introduction to North America: Both giant [49,85,98,121] and Japanese [46,98] knotweed are native to Asia. During the late 19th century, giant [42] and Japanese [98] knotweed were introduced to North America as ornamental plants. Giant knotweed was also promoted as a soil binder [42] and fodder plant [136]. One source reports Japanese knotweed established from seeds released from ship ballast in New York [6]. Giant [98] and Japanese knotweed [6,49,51,85,142,146] escaped cultivation, with herbarium records indicating that Japanese knotweed escaped cultivation at least 115 times in North America prior to 2003 [6].
Rate of spread: There is some information available regarding the rate of spread of Japanese knotweed, though as of this writing (2010) information was limited for Bohemian knotweed and lacking for giant knotweed. After initial introductions, Japanese knotweed populations displayed a 50-year lag time prior to exponential population growth. As of 2006, spread rates in the United States were increasing rapidly, while those in Canada leveled off in the 1970s [6]. In Washington, Japanese knotweed was established in one county in 1960; by 2000, it was established in more than 50 counties [127]. Along the Hoh River in northwestern Washington, one Bohemian knotweed plant was transported downstream in a winter storm event. Approximately 4 years after this event, 9,600 stems were located within 20 river miles of where this plant established. Five years after the flooding event, 18,585 stems were mapped within the same 20 river miles [111].
Means of spread: The spread of all 3 knotweeds is linked to the ability of both aboveground and belowground parts to sprout when separated from the parent plant (see Vegetative regeneration). Humans spread the plants through dumping yard waste [31,40], roadside mowing or construction projects [40], or using fill dirt from riparian areas [8]. Plants of all 3 knotweeds that escape cultivation and establish in riparian areas may spread when plant parts are transported downstream ([2,93,112,136], review by [7]). Spread by seed is rare, though it has been suggested for Japanese knotweed [141,151], and seedlings of giant [87], Japanese [16,44,74], and Bohemian [115] knotweed have been observed.
More info for the terms: adventitious, eruption, litter, rhizome, root crown
The ability for multiple plant parts to regenerate vegetatively plays an important role in the spread and establishment of the 3 knotweeds. Vegetative regeneration is possible from multiple plant parts, including rhizomes, aboveground stems, roots, and leaves.
Japanese knotweed rhizomes and roots.
Rhizomes: Giant [42,121,136], Japanese [11,49,94,103,142], and Bohemian [31] knotweed are rhizomatous. As much as two-thirds of a Japanese knotweed plant's biomass exists underground in rhizomes (review by [7]). This morphology facilitates early spring emergence and rapid growth (review by [102]) and provides sufficient reserves for plants to survive multiple losses of aboveground parts within a growing season [101]. Rhizomes of the 3 knotweeds are capable of extensive spread both horizontally and vertically. In the Pacific Northwest, the rhizomes of all 3 knotweeds penetrated at least 7 feet (2 m) into the soil and spread laterally 23 to 65 feet (7-20 m) [115]. In the Czech Republic giant knotweed rhizomes reached 50 to 65 feet (15-20 m) in length [79].
Fragment size, soil depth, and light availability impact sprouting from rhizomes. In a study of Japanese knotweed rhizome regeneration from the Slovak Republic, even 1-inch (2-cm) rhizome fragments regenerated, at a rate of 47% one year and 70% another year. Regeneration rate was higher for larger fragments than smaller fragments; 3-inch (8-cm) fragments had a 90% regeneration rate one year and 70% another year [100].
Japanese knotweed rhizomes can sprout from various soil depths; 1-inch (2-cm) depth is optimal, but rhizomes may sprout from as deep as 3 feet (1 m) (review by [7]). In New Jersey field experiments, larger Japanese knotweed rhizomes and those planted at shallower depths produced more shoots than smaller rhizomes or those planted at greater depths. One inch (2 cm) was the optimal depth for planting, though fragments left on the surface or planted as deep as 20 inches (50 cm) were able to produce shoots. Rhizome fragments could produce shoots in as little as 11 days when planted 1 inch (2 cm) deep, or 47 days for fragments planted 20 inches (50 cm) deep [74]. In the United Kingdom, 4-inch (10-cm) rhizome fragments of Japanese knotweed were buried at 2-inch (5-cm), 6-inch (15-cm), and 10-inch (25-cm) depths. By 19 days after burial, rhizome fragments at all depths sprouted, though not all shoots from rhizomes buried at the greater depths had broken the soil surface. All rhizome fragments produced adventitious roots. Although regeneration was not prevented at the depths tested, this study found poorer performance (e.g., number of shoots/shoot length) with deeper burial [45]. Both giant and Japanese knotweed regenerated vegetatively through 20-inch (50-cm) (Japanese) and 40-inch (100-cm) (giant) -thick accumulations of volcanic ash and pumice following the eruption of Mt. Usu in Japan [130].
Light may enhance the survival of sprouting rhizomes. Near Washington, DC, Japanese knotweed rhizome fragments placed on streambank sites had higher survivorship than those placed under adjacent vegetation (P<0.05). In their second year of growth, rhizomes planted on streambanks exhibited significantly greater stem growth (P<0.001), basal stem diameter (P<0.001), and stem height (P<0.01) than rhizomes planted in the understory. Streambank sites had significantly higher light levels than understory sites (P<0.01), though understory sites had more organic matter (P<0.01) [104].
Rhizomes may sprout immediately following damage but sprouting may also be delayed for years. In a study of Japanese knotweed rhizome regeneration from the Slovak Republic, rhizome fragments sprouted as early as 1 week after planting for 3-inch (8-cm) long rhizomes and 4 weeks for 1-inch (2-cm) long rhizomes [100]. In riparian areas in northwestern Oregon, some sprouts of unidentified knotweeds did not emerge for 1 to 3 years following herbicide treatments that eliminated all aboveground growth. Field excavation of a plant that appeared to be dead revealed a 6-foot (2-m) long, 1-inch (3-cm) diameter living rhizome connected to the root crown 5 inches (13 cm) below the soil surface [116]. In New Jersey field experiments, season did not affect Japanese knotweed rhizome shoot production; shoots were produced in May, July, and September [74].
Other sources of The 3 knotweeds may regenerate vegetatively from plant parts other than rhizomes. A review of Japanese knotweed biology reports that the most vigorous shoots arise in groups from perennating buds on the root crown (review by [11]). One manager from the Pacific Northwest reported that small sections of Bohemian knotweed root crowns are capable of regeneration [31].
In Pennsylvania field experiments, perennating buds formed at the base of giant knotweed seedling stems within the first growing season; these buds were the primary site of vegetative regeneration in this study, not rhizomes [87]. In the United Kingdom 4-inch (10-cm) and 12-inch (30-cm) stem fragments of Japanese knotweed were buried at 2-inch (5-cm), 6-inch (15-cm), and 10-inch (25-cm) depths. After 28 days, some of the 4-inch (10-cm) and more of the 12-inch (30-cm) stem fragments produced shoots. Although regeneration was not prevented at the depths tested, this study found poorer performance (e.g., number of shoots/shoot length) with deeper burial [45]. In the United Kingdom, cut Japanese knotweed stems floating in a canal produced axillary shoots (review by [11]). In the Pacific Northwest, Bohemian knotweed stems rooted from stem nodes [31]. Japanese knotweed cut stems may produce adventitious roots in a few days, which may be followed by axillary shoot production (review by [11]). In the Czech Republic an unidentified knotweed reportedly established from fallen leaves (Brabec 1997 as cited in [15]) though this trait has not been documented elsewhere in the literature (2010).
Root sprouting has been documented for giant knotweed. In Pennsylvania, giant knotweed seeds were planted in fields under various experimental conditions, including 3 shade levels (0%, 30%, and 63%), 2 leaf litter conditions (absent, present), and 2 seed sources. The emerging seedlings were clipped to examine their ability to sprout under the various conditions. Many of the clipped giant knotweed seedlings sprouted from the roots by June of the following year. Root sprouting was not influenced by shade treatment but failed in treatments with litter. Root sprouts grew an average of 21.2 inches (53.7 cm) in the year after clipping; the tallest was 56.7 inches (144.0 cm). Root sprouts also produced flowers and a few seeds by the end of their first growing season. The authors concluded that root reserves acquired within the first growing season were sufficient for perennial growth the next year [87].
Chile Central
| License | http://creativecommons.org/licenses/by-nc-sa/3.0/ |
| Rights holder/Author | Pablo Gutierrez, IABIN |
| Source | No source database. |
More info for the term: breeding system
- Vegetative regeneration
- Pollination and breeding system
- Seed production
- Seed dispersal
- Seed banking
- Germination
- Seedling establishment and growth
- Plant growth
It is generally accepted that asexual reproduction is the primary mode of reproduction in North America for these 3 knotweeds [74,103], though there are some reports of reproduction by seed (see Seedling establishment and growth). Near Washington, DC, 400 Japanese knotweed shoots were excavated at the periphery of stands, and all were attached to existing plants via rhizomes. No seedlings were found [103]. In Massachusetts, Japanese knotweed populations seemed to reproduce both sexually and asexually [53].
Chile Central
| License | http://creativecommons.org/licenses/by-nc-sa/3.0/ |
| Rights holder/Author | Pablo Gutierrez, IABIN |
| Source | No source database. |