Bolboschoenus medianus
Common name
purua grass
Synonyms
Scirpus medianus Cook
Family
Cyperaceae
Flora category
Vascular – Native
Endemic taxon
No
Endemic genus
No
Endemic family
No
Structural class
Sedges
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.
BOLMED
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
Distribution
Indigenous
Habitat
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.
Features
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.
Flowering
October - January
Fruiting
December - May
Life cycle
Bristly nuts are dispersed by water and possibly wind (Thorsen et al., 2009).
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.
Etymology
bolboschoenus: From Greek: bolbos (swelling or bulb) and schoinos (rush, reed), from the supposed difference from the genus Schoenus in having bulbous tubers
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.
Attribution
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