Introduced and assessed as invasive in the lower 48 states (listed as Fallopia japonica)
Ohio law lists it as an invasive plant: not native to Ohio, and causing, or likely to cause, economic, environmental or human health harm.
iNaturalist's volunteer curators list it as introduced in their Ohio checklist.
US-RIIS assesses a species as invasive when it causes, or is likely to cause, harm there, or is at least locally abundant and harmful ecologically, economically, or to health.
Season shown in 0 of Ohio's 88 counties. Explore Ohio
No result yet (44)
Recorded, too few records for a result (37)
Recorded, season not shown (7)
Season shown (0)
Boundaries: U.S. Census Bureau, 2025 Cartographic Boundary Files, 1:500,000. Show as a table
Counties as a table
Japanese knotweed by Ohio county: records and mapped range
County
Records
Adams County
Recorded, too few records for a result
Allen County
No qualifying records yet
Ashland County
Recorded, too few records for a result
Ashtabula County
Recorded, too few records for a result
Athens County
63 · Recorded, season not shown
Auglaize County
No qualifying records yet
Belmont County
No qualifying records yet
Brown County
Recorded, too few records for a result
Butler County
Recorded, too few records for a result
Carroll County
Recorded, too few records for a result
Champaign County
No qualifying records yet
Clark County
No qualifying records yet
Clermont County
Recorded, too few records for a result
Clinton County
No qualifying records yet
Columbiana County
Recorded, too few records for a result
Coshocton County
Recorded, too few records for a result
Crawford County
No qualifying records yet
Cuyahoga County
136 · Recorded, season not shown
Darke County
No qualifying records yet
Defiance County
Recorded, too few records for a result
Delaware County
Recorded, too few records for a result
Erie County
Recorded, too few records for a result
Fairfield County
No qualifying records yet
Fayette County
No qualifying records yet
Franklin County
Recorded, too few records for a result
Fulton County
No qualifying records yet
Gallia County
Recorded, too few records for a result
Geauga County
Recorded, too few records for a result
Greene County
Recorded, too few records for a result
Guernsey County
No qualifying records yet
Hamilton County
71 · Recorded, season not shown
Hancock County
Recorded, too few records for a result
Hardin County
No qualifying records yet
Harrison County
Recorded, too few records for a result
Henry County
No qualifying records yet
Highland County
No qualifying records yet
Hocking County
No qualifying records yet
Holmes County
Recorded, too few records for a result
Huron County
No qualifying records yet
Jackson County
Recorded, too few records for a result
Jefferson County
Recorded, too few records for a result
Knox County
Recorded, too few records for a result
Lake County
21 · Recorded, season not shown
Lawrence County
Recorded, too few records for a result
Licking County
Recorded, too few records for a result
Logan County
No qualifying records yet
Lorain County
Recorded, too few records for a result
Lucas County
Recorded, too few records for a result
Madison County
No qualifying records yet
Mahoning County
Recorded, too few records for a result
Marion County
No qualifying records yet
Medina County
Recorded, too few records for a result
Meigs County
No qualifying records yet
Mercer County
No qualifying records yet
Miami County
No qualifying records yet
Monroe County
No qualifying records yet
Montgomery County
Recorded, too few records for a result
Morgan County
No qualifying records yet
Morrow County
No qualifying records yet
Muskingum County
Recorded, too few records for a result
Noble County
No qualifying records yet
Ottawa County
No qualifying records yet
Paulding County
No qualifying records yet
Perry County
No qualifying records yet
Pickaway County
No qualifying records yet
Pike County
No qualifying records yet
Portage County
24 · Recorded, season not shown
Preble County
No qualifying records yet
Putnam County
No qualifying records yet
Richland County
Recorded, too few records for a result
Ross County
No qualifying records yet
Sandusky County
No qualifying records yet
Scioto County
No qualifying records yet
Seneca County
No qualifying records yet
Shelby County
No qualifying records yet
Stark County
22 · Recorded, season not shown
Summit County
92 · Recorded, season not shown
Trumbull County
Recorded, too few records for a result
Tuscarawas County
Recorded, too few records for a result
Union County
No qualifying records yet
Van Wert County
No qualifying records yet
Vinton County
No qualifying records yet
Warren County
Recorded, too few records for a result
Washington County
Recorded, too few records for a result
Wayne County
Recorded, too few records for a result
Williams County
No qualifying records yet
Wood County
Recorded, too few records for a result
Wyandot County
No qualifying records yet
No mapped range from the range source used, the USGS Gap Analysis Project, which maps land vertebrates only.
Season
When it is recorded
In Cuyahoga County
Mid-April to mid-July, middle week early May, and again late August to early January, middle week early October
Recorded in two separate seasons, each shown with its own early, middle and late weeks.
JanFebMarAprMayJunJulAugSepOctNovDec
Show over the bars
Recording in Cuyahoga County · records of all species each week, 92,154 in all
Records per week from 136 records in 10 of the 10 years from 2016 to 2025. Shows when people recorded it, not a season or how common it is.
Show as a table
Records of Japanese knotweed in Cuyahoga County each week, and records of all species
Week
Records of Japanese knotweed
Years recorded
Records of all species
Jan 4–10
0
0
468
Jan 11–17
1
1
502
Jan 18–24
1
1
393
Jan 25–31
1
1
380
Feb 1–7
1
1
590
Feb 8–14
0
0
504
Feb 15–21
0
0
455
Feb 22–28
0
0
583
Mar 1–7
1
1
567
Mar 8–14
0
0
750
Mar 15–21
0
0
819
Mar 22–28
0
0
780
Mar 29 – Apr 4
1
1
1,014
Apr 5–11
1
1
1,655
Apr 12–18
2
2
2,306
Apr 19–25
3
2
1,857
Apr 26 – May 2
17
7
4,135
May 3–9
5
4
2,830
May 10–16
10
6
2,640
May 17–23
2
1
2,938
May 24–30
4
3
2,903
May 31 – Jun 6
1
1
2,621
Jun 7–13
2
2
2,326
Jun 14–20
0
0
2,465
Jun 21–27
2
2
2,426
Jun 28 – Jul 4
6
5
2,632
Jul 5–11
2
1
2,765
Jul 12–18
6
5
2,898
Jul 19–25
0
0
2,860
Jul 26 – Aug 1
2
2
2,736
Aug 2–8
0
0
3,021
Aug 9–15
1
1
2,627
Aug 16–22
1
1
2,732
Aug 23–29
3
3
2,388
Aug 30 – Sep 5
4
4
3,076
Sep 6–12
7
5
3,578
Sep 13–19
8
5
3,735
Sep 20–26
2
2
3,328
Sep 27 – Oct 3
8
5
2,834
Oct 4–10
2
2
2,275
Oct 11–17
6
3
1,937
Oct 18–24
5
4
1,181
Oct 25–31
0
0
1,172
Nov 1–7
2
1
893
Nov 8–14
2
2
854
Nov 15–21
2
2
485
Nov 22–28
3
1
552
Nov 29 – Dec 5
0
0
448
Dec 6–12
2
2
498
Dec 13–19
1
1
458
Dec 20–26
2
2
575
Dec 27 – Jan 2
4
3
709
Reported in flower
No records here show flowers yet, so there is no flowering season to show. One needs at least 20 records from 5 different years.
Reported in fruit
Only 1 records here show fruit, too few to show a fruiting season. One needs at least 20 records from 5 different years.
In Ohio
Not enough evidence
Recorded in two separate seasons, so one season would put its middle week in the gap. Based on 763 records in 10 of the 10 years from 2016 to 2025, above the minimum of 20 records from 5 different years.
This week · Nov 8–14
JanFebMarAprMayJunJulAugSepOctNovDec
Show over the bars
Recording in Ohio · records of all species each week, 1,691,199 in all
Records per week from 763 records in 10 of the 10 years from 2016 to 2025. Shows when people recorded it, not a season or how common it is.
Show as a table
Records of Japanese knotweed in Ohio each week, and records of all species
Week
Records of Japanese knotweed
Years recorded
Records of all species
Jan 4–10
3
2
6,211
Jan 11–17
1
1
5,146
Jan 18–24
2
1
4,645
Jan 25–31
2
2
4,698
Feb 1–7
4
4
6,023
Feb 8–14
1
1
5,888
Feb 15–21
5
3
5,436
Feb 22–28
1
1
6,846
Mar 1–7
5
2
8,321
Mar 8–14
1
1
10,384
Mar 15–21
1
1
12,620
Mar 22–28
1
1
13,949
Mar 29 – Apr 4
2
2
19,661
Apr 5–11
5
4
26,860
Apr 12–18
9
3
39,925
Apr 19–25
26
8
41,623
Apr 26 – May 2
48
9
56,391
May 3–9
24
9
52,952
May 10–16
32
8
53,785
May 17–23
25
8
57,698
May 24–30
17
8
54,651
May 31 – Jun 6
13
6
53,099
Jun 7–13
19
8
53,700
Jun 14–20
11
5
56,625
Jun 21–27
11
6
55,361
Jun 28 – Jul 4
17
8
58,477
Jul 5–11
13
6
61,336
Jul 12–18
15
6
64,722
Jul 19–25
6
3
69,753
Jul 26 – Aug 1
11
6
59,416
Aug 2–8
8
5
59,712
Aug 9–15
9
5
55,994
Aug 16–22
16
8
54,328
Aug 23–29
35
8
51,772
Aug 30 – Sep 5
62
9
57,167
Sep 6–12
60
7
59,075
Sep 13–19
36
10
54,543
Sep 20–26
25
10
45,860
Sep 27 – Oct 3
30
7
43,180
Oct 4–10
23
9
37,841
Oct 11–17
39
7
30,824
Oct 18–24
22
8
21,156
Oct 25–31
18
6
19,021
Nov 1–7
11
5
14,172
Nov 8–14
12
6
12,621
Nov 15–21
7
4
7,965
Nov 22–28
3
1
8,136
Nov 29 – Dec 5
0
0
6,083
Dec 6–12
3
3
6,004
Dec 13–19
2
2
5,423
Dec 20–26
2
2
5,661
Dec 27 – Jan 2
9
3
8,459
Reported in flower
Only 18 records here show flowers, too few to show a flowering season. One needs at least 20 records from 5 different years.
Reported in fruit
Only 6 records here show fruit, too few to show a fruiting season. One needs at least 20 records from 5 different years.
What these results show
These results show when people recorded a species, not when or where it occurs. Missing weeks and low counts do not mean absence or scarcity, and counts are not abundance. Contributed records reflect where, when and what people chose to observe.
Identification
How to identify it
Telling it apart
From what Ohio’s records show. Only what the records support is shown.
American pokeweedPhytolacca americana27 identifications worldwide named one where the other was meant
Amur honeysuckleLonicera maackii22 identifications worldwide named one where the other was meant
broad-leaved dockRumex obtusifolius21 identifications worldwide named one where the other was meant
climbing false buckwheatFallopia scandens19 identifications worldwide named one where the other was meant
Japanese honeysuckleLonicera japonica18 identifications worldwide named one where the other was meant
From iNaturalist’s similar-species counts, refreshed monthly: confusions in Ohio first, then worldwide. Only species with an Ohio result are listed.
Land cover where it is recorded
Land cover
Its recordsAll Ohio records
Developed
66%49%
Forest
25%31%
Open water
4%3%
Wetland
3%5%
Farmland
2%11%
Barren
0.4%0.6%
From 502 records placed within 100 m, beside all Ohio records placed the same way. People record where they go, so this shows where records come from, not where the species lives. Land cover: USGS Annual NLCD, 2025 (opens in a new tab)
Sources
Where these results come from
Records from iNaturalist research-grade observations and expert-identified GBIF datasets, CC0, CC BY and CC BY-NC. Sources
Seasons use the published method and its evidence thresholds. Methods
A spreadsheet (CSV) with a link to each record, on iNaturalist or GBIF. Records whose location was hidden by the observer or the source are counted but not linked.
