Has been incorrectly referred to Alternanthera sessilis (L.) Roem. & Schult. by past New Zealand authors
Vascular – Native
Dicotyledonous Herbs other than Composites
The National Vegetation Survey (NVS) Databank is a physical archive and electronic databank containing records of over 94,000 vegetation survey plots - including data from over 19,000 permanent plots. NVS maintains a standard set of species code abbreviations that correspond to standard scientific plant names from the Ngä Tipu o Aotearoa - New Zealand Plants database.
2n = 28
Current conservation status
The conservation status of all known New Zealand vascular plant taxa at the rank of species and below were reassessed in 2017 using the New Zealand Threat Classification System (NZTCS). This report includes a statistical summary and brief notes on changes since 2012 and replaces all previous NZTCS lists for vascular plants. Authors: By Peter J. de Lange, Jeremy R. Rolfe, John W. Barkla, Shannel P. Courtney, Paul D. Champion, Leon R. Perrie, Sarah M. Beadel, Kerry A. Ford, Ilse Breitwieser, Ines Schönberger, Rowan Hindmarsh-Walls, Peter B. Heenan and Kate Ladley.
2012 | Not Threatened
Previous conservation statuses
2009 | Not Threatened
2004 | Not Threatened
Indigenous. New Zealand, North and South Islands. Also Norfolk Island and possibly Australia
Predominantly a coastal to lowland species of seasonally to permanently wet habitats such as lagoon, lake, pond, river, and stream margins. It has also been recorded growing within the lag zone and around burn pools of oligotrophic peat bogs in Northland and Waikato, and from salt marshes. Also an urban weed in clogged gutters, drains and in damp lawns, verges and parkland.
Perennial herbs with a slender tap root; stems prostrate to decumbent, 1.5–3.0 mm diameter, green and flushed pink, glabrous to sparsely hairy, with 2 decurrent lines of hairs, nodes tomentose. Leaves 15–45 × 3–8 mm, usually narrowly elliptic-oblong to linear-oblong, sometimes narrowly elliptic or lanceolate, dark green, midrib raised on abaxial surface, glabrate to sparsely hairy on margins, midrib, and both surfaces; apex acute; margins entire, obscurely or sparsely denticulate; base attenuate. Spikes axillary, globular or shortly oblong, 5–7 mm diameter, with 15–22 flowers, apical flowers often failing to develop; peduncle ± sessile or up to 1.0 mm long, rachis with a few pilose hairs; pedicels ± sessile or up to 1 mm long; flowers subtended by 1 bract and 2 bracteoles; bracts 0.8–1.1 × 0.6–0.7 mm, ovate, cream, glabrous, membranous, subacute to shortly acuminate; bracteoles 1.2–1.5 × 0.3–0.5 mm, lanceolate, cream, glabrous, membranous, shortly acuminate to acute. Perianth segments (tepals) 2.0–3.3 × 0.6–0.9 mm, lanceolate to ovate, keeled, cream, glabrous, membranous, apex shortly acuminate to acute; keel prominent on mature, dry tepals. Stamens 3; anthers 0.15–0.25 mm long, yellow; filaments 0.3–0.5 mm long, free part 0.2–0.35 mm long, c. 1/3 length of ovary, translucent; staminodes 3, 0.15–0.3 mm long, usually shorter than filaments. Style up to 0.1–0.15 mm long; stigma capitate; ovary 0.4–0.5 mm long, green, compressed, apex obcordate, base cuneate. Fruit indehiscent utricle, 1.7–2.2 × 1.9–2.4 mm, broadly obovoid, cream to pale green, and usually flushed pink, compressed, surface colliculate, apex obcordate, base cuneate. Seeds 0.8–1.0 mm long, broadly obovate to ± circular, cream to yellow, with a raised light brown or orange-brown centre, glabrous, smooth, compressed, apex rounded, base rounded.
Distinguished from Alternanthera sessilis (which is not present in New Zealand) by its much narrower leaves, distinctly keeled tepals, shorter staminodes, and shorter style, and from A. denticulata by its smaller stature and shorter and narrower leaves with less denticulate margins.
January - December
January - December
Urticles are dispersed by attaching to fur, feathers and clothing (Thorsen et al., 2009).
Easy from fresh seed, rooted pieces and cuttings. However can be rather weedy and aggressive.
alternanthera: From the Latin alternus ‘alternate’ and the Greek anthera ‘anther’, meaning alternating anther, probably in reference to the anthers being alternately fertile and barren.
Where To Buy
Not commercially available.
Notes on taxonomy
True A. sessilis differs from A. nahui by its much wider elliptic to rhomboidal leaves (see image from Rarotonga). Alternanthera sessilis is widespread in tropical Australia, Indonesia, Malesian, southern China and the Pacific islands.
Description from: Heenan et al. (2009): Alternanthera nahui, a new species of Amaranthaceae indigenous to New Zealand. New Zealand Journal of Botany 47: 97-105.