The New Zealand Plant Conservation Network

Species

Polygonum plebeium

Common Name(s)

Small knotweed

Current Conservation Status

2018 - At Risk - Declining

Conservation status of New Zealand indigenous vascular plants, 2012
The conservation status of all known New Zealand vascular plant taxa at the rank of species and below were reassessed in 2012 using the New Zealand Threat Classification System (NZTCS). This report includes a statistical summary and brief notes on changes since 2009 and replaces all previous NZTCS lists for vascular plants. Authors: Peter J. de Lange, Jeremy R. Rolfe, Paul D. Champion, Shannel P. Courtney, Peter B. Heenan, John W. Barkla, Ewen K. Cameron, David A. Norton and Rodney A. Hitchmough. File size: 792KB

Previous Conservation Status

2012 - Data Deficient
2009 - Data Deficient
2004 - Data Deficient

Qualifiers

2012 - SO
2009 - SO

Authority

Polygonum plebeium R.Br.

Family

Polygonaceae

Flora Category

Vascular - Native

Structural Class

Dicotyledonous Herbs other than Composites

Synonyms

Polygonum dryanderi Spreng., Polygonum aviculare var. dryanderi (Spreng.) Hook.f.

Distribution

Indigenous to Africa, India, Asia and Australia. In New Zealand there are historical (1860s) records from Great Barrier Island, and the Ruamahanga River (Wairarapa). It has also been collected in the 1940s-1950s from Lake Waikaremoana (where it is probably still present), and in the early 1990s from Lake Whangape near Huntly. In the 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.).

Habitat

Weed of dried lake, pond and river beds, salt and clay pans. Sometimes in roadside ditches.

Features

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 x 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.

Flowering

October to April

Flower Colours

Red / Pink

Fruiting

November to May

Propagation Technique

Probably easy to grow from fresh seed and cuttings.

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 4, 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.

Endemic Taxon

No

Endemic Genus

No

Endemic Family

No

This page last updated on 7 Jan 2014