Peraxilla colensoi (Scarlet mistletoe)
(unranked): Core eudicots
Species: P. colensoi
Binominal name: Peraxilla colensoi
Common names: Scarlet mistletoe, korukoru, pirita, roeroe
Peraxilla colensoi is a native parasitic shrub mainly found in silver beech forests usually at lower altitudes (up to 500 m) in the North and South Islands, from Mt Te Aroha to Southland. Its more common in southern parts of the South Island. It has been recorded on 16 host species (9 exotic). The native trees include the red beech (Fuscospora fusca), black beech (Fuscospora solandri), silver beech (Nothofagus menziesii, tawa (Beilschmiedia tawa), Metrosideros (rata) and Lemonwood (Pittosporum eugenioides)
Its scrubby plant that is up to 3 m across and have broad, leathery leaves (3-8 cm long) in opposite pairs. Only the main midrib is conspicuous on the leaves. The leaves tips are never notched and they have smooth margins that are slightly red in colour. During October – January masses of scarlet flowers heads are produced. The 60 mm long, tubular flowers are in groups of >10.
The flowers are pollinated by the Tui (Prosthemadera novaeseelandiae) and the bellbird (Anthonis melanura). the flower buds are unable to open themselves. They only open when nectar feeding birds gives the top of the flower a twist. It then immediately opens and then the bird drinks the nectar inside and fertilises the flower.
Flowering is followed by small, fleshy, oval fruit which ripen to a yellow/golden colour.
The beech mistletoes have all declined in abundance in recent decades. Their main threats are listed below:
1 Peraxilla colensoi is under threat from the Australian brushtail possum (Trichosurus vulpecula) which heavily browse mistletoes to such an extent that they are held as the primary cause for the loss of the beech mistletoes from large parts of the countries beech forests.
2 Flower predation by Zelleria maculate,a widespread endemic moth whose caterpillar feed inside the flower buds impacting the fruit set.
3 Habitat modification and loss has had an effect. Mistletoe decline is exacerbated by the serious loss of potential host beech trees in settled areas. Because of animal browsing around the beech trees, there are few beech seedlings. A beech tree has to be a couple of metres high before mistletoes will establish on it..
4 Decline of birds (chiefly bellbird and tui) associated with pollination and dispersal.
5 Fungal disease is also a problem.
Tui opening Peraxilla colensoi flower buds. Photo courtesy of Jenny Ladley