Flora of New Zealand Series

Fig 17

Inflorescence a rounded compact head, branches not evident. Flowers densely crowded.

N., S. Local throughout.

First record: Healy 1970: 136.

First collection: The earliest collection in CHR is "Wallaceville, Hutt Valley", W. F. Harris, 8.12.1944 (CHR 83481) but it is probable that var. compactus has been present in the country just as long as var. effusus.

J. effusus is distinct in the soft, easily compressed and broken stems, continuous spongy pith, and in  var. effusus, the down-curved lowermost inflorescence branches. Although some forms of J. gregiflorus and plants of J. pallidus have continuous pith and smooth green stems, the pith of J. effusus is more cobwebby and the stems much softer. J. effusus var. compactus resembles J. conglomeratus in the rounded dense-flowered heads but differs from that sp. in the stems not ridged below the heads, and in the narrow slit through which the head emerges.

Of all adventive leafless rushes J. effusus is the most widely distributed and abundant; it is little, if any less abundant than the indigenous J. gregiflorus. Though a significant element of the agricultural "rushes" complex, J. effusus is not the most troublesome as it is more frequently grazed, and is the most susceptible to herbicides. In the Westport district, a very distinct form with stems all spreading obliquely, grows with the normal erect form; this character is retained in cultivation.