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Ecological importance of Muehlenbeckia australis

Ecological importance of Muehlenbeckia australis
By Brian Patrick, Wildland Consultant Christchurch (Brian.Patrick@wildlands.co.nz)

The widespread and locally common liane, pohuehue (Muehlenbeckia australis), is endemic to New Zealand and Norfolk Island. It is one of five indigenous species of the genus in New Zealand amongst 20 species distributed from South America to Australia. They belong to the Polygonaceae—the dock family—a cosmopolitan family of shrubs, herbs and lianes.

In New Zealand, pohuehue is found from the coast through lowland regions to montane sites in hill-country and shrubland areas. This widespread liane can grow to about 10 metres tall as it winds its way up forest or forest remnants. It is a deciduous species with larger leaves than its New Zealand relatives. Patches of pohuehue can be many square metres in extent, and are typically one to two metres above ground climbing over and completely covering the supporting vegetation.

My long term observations of sites near Dunedin show that in this way it nurtures the supporting and regenerating vegetation it covers, allowing these species over time to push through the cover of pohuehue and dominate at some later time. I have seen the indigenous trees wineberry, mahoe and fuchsia regenerate within a pohuehue-dominated cover over a period of 15 years.

Ecologically it is an important native species, if not the most important species in many contexts, since it is able to survive if not thrive when sites are disturbed by felling, clearance or fire. Often, it is the only native species left following gross disturbance of indigenous vegetation. Riparian sites, gullies, hillsides and roadsides across the Canterbury Plains showcase the ‘staying power’ of this wonderful New Zealand native liane. If left to ‘dominate’ these sites, it will nurture whatever indigenous species are left on the site as stragglers or seeds, and eventually give way to these taller species. Typically, M. australis is a margin species, covering the edge of forest or shrubland patches and protecting forest edges from the ravages of wind damage. Without its survival in these disturbed landscapes, many indigenous insects would not be able to survive there and provide food for indigenous reptiles and birds.

Our single most important hostplant 
From and entomological perspective, pohuehue is the single most important host plant with tens of indigenous insects depending on it, many of which also feed on its sister species M. complexa. It supports diverse orders of insects such as our sole praying mantis, many stick insects, myriad flies, lacewings, wasps, bugs, moths, butterflies and beetles. Among the butterflies and moths, it is the most eaten New Zealand plant supporting many groups of these insects as follows. The list includes both specialists and species that feed on other indigenous plants in addition to pohuehue:

• Three of our four copper butterflies depend on it with the fourth group, the boulder coppers feeding on its smaller relative M. axillaris. With green sluglike larvae feeding on M. australis are Lycaena edna, L. salustius, L. feredayi, L. enysii and L. rauparaha and at least 10 other undescribed species of copper illustrated and recognized in Patrick and Patrick (2012).

• Four noctuid moths—large attractive nocturnal moths—including Bitlya defigurata, B. sericea, Meterana coeleno and M. stipata are specialists on this liane. Another three noctuids also feed on it amongst a range of other native plants

• Many geometrid moths are specialists on this host plant including Chloroclystis sphragitis on the flowers; Pseudocoremia indistincta on the foliage; Pasiphila muscosata on foliage; and many others, including Declana floccosa, D. leptomera, Gellonia dejectaria, and Homodotis megaspilata,regularly feed on the foliage or freshy fallen leaves

• Our sole thyridid moth, Morova subfasciata, has larvae that form a swelling on the stems of pohuehue within which the larvae feed on the plant’s tissue. The adult moths are attractive orange day-flying moths that are widespread in New Zealand.

• Several crambid moths have larvae that are leafrollers on the foliage including the orange Udea flavidalis

• Specialised leafrollers in the family Tortricidae include several in the genus Pyrgotis, Harmologa amplexana and the polyphagous Planotortrix excessana, Catameacta gavisana and Ctenopseustis obliquana, are commonly found on this host plant.

• The day-flying moth, Zapyrasta calliphana (Family Momphidae), has larvae that form leaf mines in the leaves within which they feed protected.

• The large case moth, Liothula omnivora, often feeds on pohuehue foliage where its long larval cases are conspicuous.

• Many leaf litter oecophorid moths feed on the fallen leaves of this deciduous host plant. These moths are in the genera Tingena, Trachypepla and Gymnobathra.

Overall, pohuehue is the most important indigenous New Zealand plant for our indigenous insects, particularly moths and butterflies. Together with its ecological importance in both survival and nurturing, it assumes fundamental importance across our landscapes, both natural and disturbed.

Reference Patrick, B., Patrick, H., 2012: Butterflies of the South Pacific.
Otago University Press, Dunedin. 240p. Editor’s Note: This item was first published by the Queen Elizabeth II National Trust; published here with the author’s permission.