Why are kawakawa falling over?

In Birdwood Reserve, near where I live, there’s been an epidemic of some sort affecting kawakawa, Piper excelsum.  Large plants lose their leaves and the roots seem to die off, because the whole plant falls over, as if wind-thrown.  There are still plenty of small plants alive, so it's not wiping them all out:

Kawakawa is very susceptible to spray damage, and certainly some of these dead plants are alongside tracks where weeds have been sprayed lately.  I’ve found the slightest spray drift of glyphosate is enough to wither kawakawa leaves and slowly kill the plants.

But some of these plants were growing where I don’t think there would have been any spraying, so I’m wondering if a disease is involved.  Indeed one such dead plant is in my garden, where I certainly haven't sprayed, but where nevertheless quite a few plants (not just kawakawa, but also northern rata (Metrosideros robusta) and akeake (Dodonaea viscosa)) have suddenly died.  The weather has been normal, except for the snowfall in August. 

In cabbage trees (Cordyline) sudden decline is caused by a phytoplasma.  This is an extremely small bacterium that's spread by sap-sucking leaf hoppers.  So far it's been implicated in deaths of cabbage trees, strawberries, coprosmas, and Phormium (New Zealand flax) (Liefting et al., 2007).  I've no reason to suspect any particular cause in this case, but the cabbage tree disease does show how devastating these things can be.

I'd be interested to hear if anyone else has observed similar collapse of kawakawa anywhere.

Reference

Lia W. LIEFTING, Ross E. BEEVER, Mark T. ANDERSEN, Gerard R. G. CLOVER Phytoplasma diseases in New Zealand.  Bulletin of Insectology 60: 165-166 (2007).

White mignonette

Reseda alba, Karori, Wellington, New Zealand

Resedaceae is a small family in the glucosinolate-producing Order Brassicales.  Reseda alba, white mignonette, is a cottage garden flower grown for the sweet scent of the flowers, and it’s naturalized in New Zealand.  These ones were semi-wild on a crib wall in Karori, Wellingon.

Wellington coast at Makara

We took a great little walk today from Makara towards Opau Bay, along a section of Wellington coast.  The walk itself is described here, but I want to write about some of the plants.

The coastal cliffs are formed along the Ohariu Fault, one of the three main fault lines that define, and threaten, Wellington.  The cliffs are about 180 m tall here, and not so steep that you can’t scramble down them in most places.  Still, they give spectacular views up the coast to Kapiti and Mana Islands and westward across Cook Strait to the South Island.

Looking north from the cliff top.  Mana Island with Kapiti Island behind; Pukerua Bay headland (distant right) and Pipinui Point (closer, right)

East of the cliffs, it’s sheep farming country, but now also a wind farm.  The huge turbines were spinning slowly in today’s gentle breeze.

Down on the coast, it's pretty weedy, but a few native plants persist here.  Tetragonia is an edible, scrambling, slightly fleshy, plant in the ice-plant family Aizoaceae; this one is probably T. trigyna.

Tetragonia trigyna

A relative in the same family was also common on the coast: Disphyma australe.

Disphyma australe

At the high point of the track, there are more turbines, and on the cliff top two old gun emplacements from World War II.  Here the track descends again towards Opau Bay.

Looking south to Opau Bay

In the gully here a few trees of Pennantia corymbosa form the beginnings of a low forest among the mostly native scrub of tauhinu and coprosma.

Pennantia corymbosa

A few plants of Clematis forsteri were in flower among the scrub.  Sabrina said they smelled like feijoa fruit and she could smell them from a few metres away, whereas I could detect no scent even close up.  Callum said feijoa too, independently.  All the ones we saw were male.

Clematis forsteri

The flowers are pale yellow, and hairy on the backs of the sepals:

Clematis forsteri male flower

One patch was heavily infested with a rust fungus that distorted the growth of stems and leaves.  The little pink dots on the right hand piece are pustules where spores are released.

Clematis forsteri, infected by rust fungus (right) and not infected (left).

Some quite spectacular weeds grow in places along the coast.  Artemisia arborescens is a common hedge plant in coastal areas and has probably spread here from the nearby settlement.

Artemisia arborescens.

Aloe saponaria was growing beside one of the gun emplacements.  I wonder if it was originally planted there by the gun crews.

Aloe saponaria

Although we had an almost still day, there's no doubt this is a windy coast.  First of course, the decision to put a wind farm here reflects that, but also many of the plants are wind-shorn.  This Melicytus alpinus was so stunted that it was almost a solid outer shell of wood, with a few fleshy leaves attached.

Melicytus alpinus.

They say you can't beat Wellington on a good day.  I think the statement is deliberately ambiguous; it could refer to the rugby team, or to the weather.  Whatever, today was a good day.