DOI: 10.5061/dryad.79cnp5j9k
title: Data from: Sexual reproduction in invasive Japanese knotweed (<em>Reynoutria japonica</em>) in south Sweden

description: To understand the potential for northward expansion of knotweeds into
 currently uninvaded regions, it is crucial to assess the potential for
 sexual reproduction alongside the ongoing vegetative spread. For that
 reason, we tested viability in Reynoutria japonica seeds in south Sweden,
 a region where viable seeds had not been previously reported. Knotweed in
 northernmost Europe has no genetic variation, indicating a lack of fertile
 seeds, and northward colonization is considered limited by temperature and
 a short growing season. Observations of profuse flowering and seed
 production in recent years, however, prompted us to test seed germination.
 Seeds from 7 localities in Scania and 20 localities in Halland in southern
 Sweden were collected in October and November 2021 and 2023 and germinated
 under laboratory conditions. In Scania, seeds from six out of seven stands
 germinated with an average germination of 57,7 ± 32,1%. A second trial, 10
 months after seed collection, showed 48,0 ± 14,2% germination on seeds
 from two of the sites. In Halland, seeds collected in November 2023
 germinated with an average germination of 78,13± 20,71%, and germination
 in soil was 15% ± 16,1. Field inventories detected seedlings that were
 determined by metabarcoding to be R. japonica ×F. baldschuanica hybrids.
 Collected R. bohemica ×F. baldschuanica seeds from one site were fertile,
 and the seedlings survived cool conditions for 2 winters. We established
 that R. japonica produces viable seed in south Sweden, which is further
 north than previously demonstrated in Europe. The observation that F.
 baldschuanica was a common pollen donor concurs with studies from other
 parts of Europe. Presence of fertile seeds and seedlings has implications
 for the northward dispersal of knotweeds in Europe. Russian vine (F.
 baldschuanica) was identified as the pollen donor for R. japonica stands
 and one putative R. bohemica stand in South Sweden.
description: # Data from: Sexual reproduction in invasive Japanese knotweed
 (*Reynoutria japonica*) in south Sweden Dataset DOI:
 [10.5061/dryad.79cnp5j9k](https://doi.org/10.5061/dryad.79cnp5j9k) ##
 Description of the data and file structure Seeds of Japanese knotweed
 (*Reynoutria japonica*) from 7 localities in Scania and 20 localities in
 Halland in southern Sweden were collected in October and November 2021
 (Scania) and 2023 (Halland) and germinated under laboratory conditions.
 The coordinates for the sites are provided in Tables 1 and 2. In Scania,
 seeds from six out of seven stands germinated with an average germination
 of 57,7 ± 32,1% (data for Fig.2). A second trial 10 months after seed
 collection showed 48,0 ± 14,2% germination on seeds from two of the sites
 (data for Fig. 2). In Halland, seeds collected in November 2023 germinated
 with an average germination of 78,13± 20,71%, and germination in soil was
 15% ± 16,1 (Data provided in table for Fig. 3, 4, 5). ### Files and
 variables #### File: NJB_Dryad_repository_data.xlsx **Description:** 
 Seeds were germinated in petri dishes and seeds were either intact (with
 calyx) or germianted with the calyx removed.  ##### Variables * Site
 coordinates for Scania are provided in WGS84 and DDM (Table labelled Fig
 1) * Site coordinates for Halland are provided in SWEREF 99 ±10 meters
 (Table labelled Fig 1 Table 2) * Table labelled Fig 3,4,5 is data for
 Halland, petri_mm is length in millimeters for seeds germinated in petri
 dishes and petri_g is weight of seeds in grams. W_L is the seed weight in
 milligrams  divided by seed length in millimeters. Germination petri is
 the percentage of seeds germinated in petri dishes. * Table labelled Fig 6
 is data for seed germination in soil. Seed weight is the average seed
 weight for the seeds in soil. * Table labelled Fig 7 summarizes where
 Reynoutria species (Reynoutris sp) were found in relation to Reynoutris
 that seeds were sampled from in the study. * Metabarcoding and
 Metabarcoding sites: Field inventories detected seedlings that were
 determined by metabarcoding to be *R. japonica* ×*F. baldschuanica*
 hybrids and the results are summarized in the metabarcoding table. The
 data shown are the counts for mutations for the ITS  and RbcL (maternal
 plastid) marker genes, respectively. Metabarcoding analyses were performed
 by the Centre for Genetic Identification at the Swedish Museum for Natural
 History and are available there as Open Access (Report 356-2025) including
 the site and co-ordinates. ## Code/software Any program that will open a
 spreadsheet, such as Excel is recommended. ## Access information Other
 publicly accessible locations of the data: * none Data was derived from
 the following sources: * none