Acaena inermis
Common names
blue mountain bidibid, spineless bidibid
Biostatus
Native – Endemic taxon
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 | Not Threatened
Category
Vascular
Structural class
Herbs - Dicotyledons other than Composites
Simplified description
An evergreen dull green to purple herb, which grows in loose mats up to a 1/2 metre or so across and about 4cm in height. The pinnate leaves are delicate and blunt-toothed, may appear overlapping. The globe shaped flower balls are white in bloom and grow into a cluster either lacking noticeable spikes or having more or less 1 cm long red barbless spines which when ripening become light brown or cream coloured.
Flower colours
White
Detailed description
Rhizomatous; prostrate, trailing perennial herb, forming a loose mat up to 1/2 metre or more in diameter. Stems approximately 1.2 mm diameter, sparsely hairy, up to 15 cm long, and/or 4 cm high, rooting at nodes; Stipules entire, narrow; Leaves odd-pinnate, between 15-70 mm long with 11-15 leaflets; Leaflets orbicular, serrated toothed margin, teeth blunt or rounded, 7-12 teeth per leaflet not hair-tipped, lower leaflets smaller, distinctly dull green, grey, olive or purplish on both surfaces, veins and margins of lower surface hairy; Inflorescence scape 1-50 mm, brown/orange, covered with fine shaggy hairs; Capitulum of approximately 20 florets, each floret has 4 sepals, 2 stamen, white anthers, 1 white style, 1 achene; Fruit roughly cone-shaped, each having 4 non-barb tipped spines or no spines, up to 13mm long, mature dry, pale brown to cream when ripe.
Similar taxa
Acaena tesca, very similar. This species is only known from lower third of the South Island, East of the Alps. The capitulum is almost stemless, having only 10 florets (compared to 20); Leaflets are hair-tipped and sharp toothed, compared to blunt-toothed and lacking hair-tipped as seen in A. inermis.
Acaena caesiiglauca, similar colour and quite a range of colours as in A. inermis. stoloniferous rather than rhizomatous; stipules perfect to bifid; only up to 11 leaflets (compared to 11-15 in A. inermis); leaflet teeth are sharply pointed rather than rounded, have a hairy tip; scape up to 200 mm, rather than up to 75 mm; 50-70 florets rather than only 20 florets per capitulum; fruit spikes have barbs, rather than lacking barbs or hairs.
Acaena saccaticupula another bluish-green species, stipules are trifid-pentafid rather than entire; anthers are red rather than white.
Distribution
Endemic. Central North Island. South Island, mostly in the East, occasionally in West.
Habitat
Montane to alpine (300-1000 m.a.s.l.), grasslands and riverbeds.
Detailed taxonomy
Genus
Family
Endemic taxon
Yes
Endemic genus
No
Endemic family
No
Ecology
Flowering
November- January(-March)
Fruiting
November-May
Other information
Etymology
acaena: From the Greek ‘akanthos’ thorn, referring to the spiny calyx that many species have
inermis: Not spiny, unarmed
NVS code
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.
ACAINE
Chromosome number
2n = 42
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 | Not Threatened
2012 | Not Threatened
2009 | Not Threatened
2004 | Not Threatened
Regional conservation statuses
Otago: 2025 | Regionally At Risk – Regionally Declining | Qualifiers: DPS, DPT, NStr, RR
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
References and further reading
Allan HH. 1961. Flora of New Zealand. Volume 1. Indigenous Tracheophyta: Psilopsida, Lycopsida, Filicopsida, Gymnospermae, Dicotyledones. Government Printer, Wellington, NZ. pg. 356.
Lloyd K. 2001. A Key and notes for Acaena (Rosaceae) in New Zealand. Botanical Society of Otago Newsletter 25. Pgs. 10-14.
Attribution
Fact sheet prepared for NZPCN by MD Ward (August 29th 2025). Description adapted from Lloyd (2001), Allan (1961).