Chatham Island aster, swamp aster, hanga-tare
Vascular – Native
Trees & Shrubs - Dicotyledons
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 = 108
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 | At Risk – Naturally Uncommon | Qualifiers: IE, RR
Previous conservation statuses
2009 | At Risk – Naturally Uncommon | Qualifiers: IE
2004 | Range Restricted
Small tree with narrow leathery saw-edged dark green leaves that are white underneath and large pinkish-purple daisy-like heads inhabiting swamps on the Chatham Islands. Leaves 3.5-7cm long by 0.5-1cm wide, widest at middle, with large thick teeth spaced along edge. Flowers 2.5-3.5cm wide.
Endemic. Chatham Islands only
More or less confined to restiad bog where it is one of three woody shrubs capable of growing amongst Sporadanthus traversii (the others are mataira karupuru (Myrsine coxii) and Dracophyllum scoparium). It is a rapid coloniser of burnt peat bog.
Spindly, erect, sparingly branched shrub up to 2 m tall, trunk erect, slender and brittle; bark grey, grey-brown, chartaceous, flaking readily. Branches erect to suberect, (2–)4(–6) mm diameter, quadrangular, brittle, young branches densely invested in white floccose tomentum; tomentum discolouring and shedding in irregular patches as branch matures. Leaves alternate, subsessile, coriaceous; petiole if present, 1.5-2.6 mm long, plano-convex, densely covered in white, appressed to floccose hairs; lamina 30-74(-80) × 6-9(-12) mm, narrow-lanceolate, lanceolate to oblong-lanceolate, adaxially dark green, glossy, initially moderately densely to sparsely covered in white appressed floccose / lanate hairs, glabrescent abaxially, thickly covered in white, appressed hairs, margins weakly, rarely prominently, serrate in distal half to one third, teeth when present in (6–)8–10 pairs, sometimes entire; apex acute, subacute; base shortly attenuate. Inflorescences numerous at apex of branches, terminal, subterminal, axillary. Peduncules 50-80(-100) mm long, initially erect or curved, then spreading, slender (3–6 mm diameter), terete, white tomentose, bracteate, bracts 1-3-many, lanceolate, entire or toothed (2-3)4×, surfaces copiously white, tomentose. Capitula (30–)40 mm diameter. Involucrellum narrowly urceolate to obconic, involucral bracts imbricate, numerous, up to 10 mm long, narrowly lanceolate, deltoid, acute, abaxially maroon-black, covered in pilose / cob-webbed hairs, hairs especially prominent on margins; ray-florets (24-)26-30, 10-12 × 4-5(-6) mm, glabrous, linear-oblong, oblanceolate, apices obtuse, subacute or acute, usually minutely retuse, mucronate, mucro minute; surfaces initially purple, maturing lilac often fading to white tinged lilac; disc-florets(20-)22-26, corolla, magenta to violet-purple, anthers orange yellow, stigma dark magenta. Cypsela 2.5–4.2 mm long, narrowly oblong, narrowly obtriangular, obovate-triangular, compressed, often biconvex, base cuneate, ribbed 8–11, otherwise smooth, almost glabrous, sparsely furnished with short, white antrorse hairs, sparsely glandular, surface brown to grey-brown. Pappus 4.5–6.2 mm long, buff, pale orange-yellow.
Easily distinguished from the other macrocephalus species of Olearia by the spindly, sparingly branched shrub growth habit (specimens up to 2 m tall), short and dark mauve (rarely pink) ray florets. On the Chatham Islands hangatere (Olearia semidentata) could only be confused with keketerehe (O. chathamica). However, keketerehe is a much larger more heavily branched small tree (6–8 m tall) that usually forms a broadly domed canopy. The leaves of keketerehe are much longer, and more finely denticulate than those of hangatere which are shorter sparingly, or coarsely toothed in the upper half to third, while the capitula of keketerehe have dark aubergine coloured disc florets, and longer, narrower, white, white tinged pinkish (very rarely pale mauve) ray florets. Occasional hybrids between hangatere and keketerehe have been collected, notably from Rangaika where the ranges of both species overlap due to past land disturbance along the fringes of a restiad bog.
November - March
January - June
Threatened by loss of habitat through peat bog drainage, over burning of restiad bog, accompanied by drying out of the peat soils, and also by browsing pressure from cattle.
olearia: Named after Johann Gottfried Olearius, a 17th-century German scholar, writer of hymns and author of Specimen Florae Hallensis
semidentata: Partially toothed
Where To Buy
Not commercially available.
Fact Sheet prepared for NZPCN by P.J. de Lange 28 April 2022. Description by P.J. de lange (27 April 2022).
Please cite as: de Lange, P.J. (Year at time of access): Olearia semidentata Fact Sheet (content continuously updated). New Zealand Plant Conservation Network. https://www.nzpcn.org.nz/flora/species/olearia-semidentata/ (Date website was queried)