Bolboschoenus medianus


Bolboschoenus: From Greek: bolbos (swelling or bulb) and schoinos (rush, reed), from the supposed difference from the genus Schoenus in having bulbous tubers

Common Name(s)

Purua grass

Current Conservation Status

2012 - Not Threatened

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

2009 - Not Threatened
2004 - Not Threatened


Bolboschoenus medianus (Cook) Soják



Flora Category

Vascular - Native

NVS Species 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.

Structural Class



Scirpus medianus Cook




Coastal to lowland in saltmarshes and other poorly drained saline areas, occasionally found along freshwater rivers and lakes. Sometimes invades pasture abutting tidal streams and estuaries.


Summer-green, bulbous perennial forming mostly densely clumped patches. Rhizome 3-5 mm diameter, woody, horizontal, long-creeping, dark brown, apices terminated by globose, ligneous tubers. Culms 1(-2) per tuber, 0.7-1.5 m tall, 4-5 mm diameter, triquetrous, striated, smooth except just below inflorescence where scabrid on angles; basal sheaths loose, membranous, septate, brown. Leaves numerous, more or less equal to, or greater than culms, 450-500 x 6-8 mm, double-folded but flattened, grass-like, tapering, coriaceous, margins and midrib scabrid towards apices; sheaths long, closed, coriaceous. Inflorescence a terminal, compound, irregular umbel; rays 4-6, unequal, 20-100 mm long, bearing clusters of 1-6 spikelets, a sessile glomerule of spikelets at the base of the rays; involucral subtending bracts similar to leaves, greater than inflorescence, unequal, 150-250 x 3-6 mm, as many as, or 1-2 fewer than rays. Spikelets 10-20 mm long, ovoid, or more or less cylindric, dull red-brown. Glumes membranous, pubescent, apices cleft or lacerate, with a scabrid, recurved awn. Hypogynous bristles up to 6, in length < nut, persistent or shedding, red-brown, retrorsely scabrid. Stamens 3. Style-branches 2-3. Nut 3.0-4.0 x 2.0-2.5 mm, obovate, dorsiventrally compressed and plano-convex or trigonous with obtuse dorsal angle and convex sides, apiculate, maturing greyish to black and glossy.

Similar Taxa

Distinguished from the other two indigenous species, B. caldwellii caldwellii (Cook.) Soják and B. fluviatilis (Torr.) Soják by the nuts with are compressed rather than trigonous (as in B. fluviatilis) and with convex rather than depressed (concave) sides (as in B. caldwellii) and by the 2-3 style branches, rather than consistently 2 in B. caldwellii or mostly 3 in B. fluviatilis.


October - January


December - May

Propagation Technique

Easily grown from fresh seed and rooted pieces. Will grow in almost any soil but prefers a sunny, damp soil. Ideal as a pond plant or for planting along tidal streams.


Not Threatened

Endemic Taxon


Endemic Genus


Endemic Family


Life Cycle and Dispersal

Bristly nuts are dispersed by water and possibly wind (Thorsen et al., 2009).

Where To Buy

Not commercially available

Cultural Use/Importance

In the Waikato this species is abundant along the tidal stretches of the Piako and Waitoa Rivers of Hauraki Plains, the Waikato River (to about Taupiri) and also around the larger lakes of the Huntly Basin.


Description adapted from Moore and Edgar (1970)

References and further reading

Moore, L.B.; Edgar, E. 1970: Flora of New Zealand. Vol. I. Government Printer, Wellington.

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 2009 Vol. 11 No. 4 pp. 285-309

This page last updated on 14 Aug 2014