Tuesday, 8 October 2013

Wednesday Wildflower: boobialla (Tasmanian ngaio)

Bird-dispersed woody weeds are some of the worst, and many in New Zealand are escapes from horticulture.  Sometimes there are similar native and weedy species that can be confused.
Shoots of ngaio (left) and boobialla.
Ngaio is a case in point.  True ngaio, Myoporum laetum, is a native plant, and a good one to use in revegetation projects because it's easy and quick to grow.  But the problem is there's also an introduced Myoporum from Tasmania, M. insulare, which is also quick-growing.  If the Tasmanian ngaio, often known by its Australian common name, boobialla, is misidentified as the New Zealand native, then it can become widespread in an area by accident.  Because they're both bird-dispersed, both ngaios can spread rapidly.
Plantings between Nelson and Atawhai.
There's a good example of this in Nelson, between the city and Atawhai.  Alongside a new walkway/cycleway, an attractive native revegetation area is flourishing.  Many native trees and shrubs are doing well there, such as Griselinia litoralis, Cordyline australis, Dodonaea viscosa, Phormium tenax, and Coprosma robusta.  Unfortunately, most of the ngaio planted there is the wrong species: boobialla.
New leaves of ngaio (left) and boobialla.
The two are quite similar.  Ngaio has purplish brown new leaves at the tips of the shoots while those of boobialla are green.
Leaves of ngaio (left) and boobialla.
The leaves of ngaio have more obvious glandular dots than boobialla does.

Flowers of ngaio (left) and boobialla.
The flowers are a bit different too: those of boobialla are a bit smaller, more symmetrical, and have fewer and less obvious dots on the corolla.

While we can grumble about an Australian plant taking over the role of ngaio in New Zealand, the New Zealand ngaio isn't wanted everywhere.  It's becoming a weed in California, along with cabbage tree and pōhutukawa.  I'll post soon about an interesting new research paper that deals with this.

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