Polygonum plebeium
Common names
small knotweed
Biostatus
Native
Current conservation status
The conservation status of all known New Zealand vascular plant taxa at the rank of species and below were reassessed in 2022-2023 using the New Zealand Threat Classification System (NZTCS) – more information about this can be found on the NZTCS website. This report includes replaces all previous NZTCS lists for vascular plants. Previous assessments can be found here.
- Conservation status of vascular plants in Aotearoa New Zealand, 2023. 2024. Peter J. de Lange, Jane Gosden, Shannel P. Courtney, Alexander J. Fergus, John W. Barkla, Sarah M. Beadel, Paul D. Champion, Rowan Hindmarsh-Walls, Troy Makan and Pascale Michel Department of Conservation. Source: NZTCS and licensed by DOC for reuse under the Creative Commons Attribution 4.0 International licence.
2023 | At Risk – Declining | Qualifiers: DPR, DPS, DPT, SO
Category
Vascular
Structural class
Herbs - Dicotyledons other than Composites
Flower colours
Red/Pink
Detailed description
Prostrate, annual to short-lived perennial, nearly hairless, grey-green, mat-forming herb. Stems < 15 cm long (rarely 30 cm long), angled, angles minutely hairy. Leaves grey-green to blue-green, unstalked (sessile), 3–9 × 0.5–1.5 mm, linear, linear-oblong or spathulate, with entire margins. Leaf midrib conspicuous, but lateral veins not evident. Ochreae (papery sheath encircling stems below leaves) 3 mm long, enclosing half of the internode between leaves, silvery-translucent, apex soon becoming lacerated. Flowers pink, axillary, in clusters of 1–5, stalks (pedicels) 0.5 mm long at flowering, usually enclosed by ochreae. Nut 1.2–1.7 mm, ovoid, dark brown or black, smooth, glossy 3-angled with ridges rounded.
Similar taxa
Polygonum plebeium can only be confused with another common knotweed P. aviculare L.. From this species it is best distinguished by the leaves lacking obvious lateral veins, and by the smooth and glossy nuts. It is usually a smaller plant but some recent collections suggest that size may be a function of local habit conditions.
Distribution
Indigenous. New Zealand: North Island (historical (1860s) records from Great Barrier Island (Aotea Island) and the Ruamahanga River (Wairarapa). It has also been collected in the 1940s–1950s from Lake Waikaremoana (where it may still be present), and in the early 1990s from Lake Whangape near Huntly), South Island (despite Buchanans early, apparently unsubstantiated records, it was first definitely gathered in 1995 from Otematata, and has since been found in several other central Otago sites, where in places it can be common (B. Patrick pers. comm.)). Also Africa, India, Asia and Australia.
Habitat
Weed of dried lake, pond and river beds, salt and clay pans. Sometimes in roadside ditches.
Threats
Polygonum plebeium has been listed as Data Deficient because it seems to be genuinely scarce and it may be indigenous. Currently it is treated as naturalised in Flora IV, although even there it is suggested that it might be native. The issue is confused because the colonial botanist John Buchanan listed it (as P. dryanderi) as spreading rapidly from the Dunedin docks into parts of central Otago during the gold rush of the 1860s. Although his record does not seem to be substantiated by herbarium specimens, the majority of modern collections have come from Otago. Threats to the species are not immediately obvious, though it seems to have virtually died out in the North Island.
Detailed taxonomy
Genus
Family
Synonyms
Polygonum dryanderi Spreng., Polygonum aviculare var. dryanderi (Spreng.) Hook.f.
Endemic taxon
No
Endemic genus
No
Endemic family
No
Ecology
Flowering
October–April
Fruiting
November–May
Propagation technique
Probably easy to grow from fresh seed and cuttings.
Other information
Previous conservation statuses
The conservation status of all known New Zealand vascular plant taxa at the rank of species and below were reassessed in 2022-2023 using the New Zealand Threat Classification System (NZTCS) – more information about this can be found on the NZTCS website. This report includes replaces all previous NZTCS lists for vascular plants. Previous assessments can be found here.
- Conservation status of vascular plants in Aotearoa New Zealand, 2023. 2024. Peter J. de Lange, Jane Gosden, Shannel P. Courtney, Alexander J. Fergus, John W. Barkla, Sarah M. Beadel, Paul D. Champion, Rowan Hindmarsh-Walls, Troy Makan and Pascale Michel Department of Conservation. Source: NZTCS and licensed by DOC for reuse under the Creative Commons Attribution 4.0 International licence.
2017 | At Risk – Declining | Qualifiers: DP, SO
2012 | Data Deficient | Qualifiers: SO
2009 | Data Deficient | Qualifiers: SO
2004 | Data Deficient
Regional conservation statuses
Auckland: 2025 | Regionally Extirpated
The regional threat classification system leverages off the national assessments in the NZTCS, providing information relevant for the regional context. Auckland conservation status information is sourced from the “Conservation status of vascular plant species in Tāmaki Makaurau / Auckland” Simpkins E et al. (2025) report.
Otago: 2025 | Regionally Data Deficient
The regional threat classification system leverages off the national assessments in the NZTCS, providing information relevant for the regional context. Otago conservation status information is sourced from the “Conservation Status of Indigenous Vascular Plants in Otago, 2025” Jarvie S et al. (2025) report.
Referencing and citations
Attribution
Fact sheet prepared by P.J. de Lange for NZPCN (1 June 2013)
NZPCN Fact Sheet citation
Please cite as: de Lange, P.J. (Year at time of access): Polygonum plebeium Fact Sheet (content continuously updated). New Zealand Plant Conservation Network. https://www.nzpcn.org.nz/flora/species/polygonum-plebeium/ (Date website was queried)