Helms crassula, New Zealand pygmyweed
Tillaea helmsii Kirk
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 = 14
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 | Qualifiers: SO, Sp
Previous conservation statuses
2009 | At Risk – Naturally Uncommon
2004 | Sparse
?Endemic. In New Zealand known only from the West Coast of the South Island from Karamea south to just south of Haast. Naturalised in Britain where it is regarded as a serious weed.
Coastal to lowland, in shallow pools of fresh water or in damp usually shaded places, such as under rock overhangs, near waterfalls, and in shallow, slowly moving water. Occasionally it has been collected growing in exposed conditions on cobble beaches and gravel bars, but only where there is abundant fresh water flowing close to the surface.
Perennial, decumbent, herb forming diffuse to extensive mats. Stems green, pink or white, succulent, prostrate, rooting at nodes, ascending at tips, heavily branched. Leaves fused at base 2-7(-10) x 0.7-2 mm, 0.5-0.8 mm thick when fresh, narrowly lanceolate, oblong-lanceolate or elliptic-lanceolate, flattened above, strongly convex below, apex rounded or acute. Flowers solitary in leaf axils, fragrant, stellate, 4-merous, 3-4 mm diam.; pedicels 2-7 mm, not elongating at fruiting. Calyx lobes 1-2 x 0.5-0.6 mm, triangular-ovate, acute or subacute. Petals 1.2-2 x 0.8-1 mm, broadly elliptic-ovate, white with pink flush or pink, subacute > calyx. Scales 0.7 mm, oblanceolate. Follicles smooth. Seed 0.5 mm.
Distinguished from all other indigenous species of Crassula by the broadly-elliptic petals, whose length is 1.7x the width, and by the leaves which are 2-10 x 0.7-2 mm. In some respects it resembles a diminutive or elongated form of C. moschata G.Forst. - a strictly coastal, always terrestrial species, which has much larger flowers, and thicker leaves. C. helmsii can be very variable.
Flowers may be present throughout the year
Fruit may be present throughout the year
Minute follicles are dispersed by wind and water and possiblty also by attachment (Thorsen et al., 2009).
Easy from rooted pieces, and stem cuttings. Does best in damp soils or partially submerged, can become invasive. The white to pale pink flowers are sweetly scented
It is not clear if this species is actually threatened however, it does appear to be rather uncommon with a patchy distribution throughout its range in New Zealand.
crassula: From the Latin crassus ‘thick’, meaning ‘rather thick’
Notes on taxonomy
Crassula helmsii which was first described from New Zealand has often been treated as indigenous to New Zealand and Australia. However the New Zealand plant is much smaller and more delicate than the Australian plant, and recent studies have shown that it can be distinguished from Australian plants by its diploid (2n = 14) rather than hexaploid (2n = 42) chromosome number, different nrDNA ITS sequence, and ecology. On this evidence Australian plants might better be referred to as C. recurva (Hook.f) Ostenf. However, further sampling from both countries is needed to confirm these observations. It would appear that it is the New Zealand plant which is naturalised in Britain.
Fact sheet prepared for NZPCN by P.J. de Lange 1 February 2008. Description based on Webb et al. (1988)
References and further reading
Webb CJ, Sykes WR, Garnock-Jones PJ 1988. Flora of New Zealand. Vol. IV. Botany Division, DSIR, Christchurch.
Thorsen, M. J.; Dickinson, K. J. M.; Seddon, P. J. 2009. Seed dispersal systems in the New Zealand flora. Perspectives in Plant Ecology, Evolution and Systematics 11: 285-309
Please cite as: de Lange, P.J. (Year at time of access): Crassula helmsii Fact Sheet (content continuously updated). New Zealand Plant Conservation Network. https://www.nzpcn.org.nz/flora/species/crassula-helmsii/ (Date website was queried)