Systematics, biology and ecology of New Zealand's pygmy mistletoes (Korthalsella: Viscaceae) : a thesis presented in partial fulfilment of the requirements for the degree of Doctor of Philosophy in Ecology at Massey University, Manawatu, New Zealand
New Zealand’s pygmy mistletoes belong to the genus Korthalsella Tieghem,
which comprises about 30 species ranging from Malesia to Hawaii, the Marquesas and
Henderson Islands in the east, Japan in the north, Australia, New Zealand in the south,
and Ethiopia and Madagascar to the west. Mainland Australia, Hawaii, Malesia and
Madagascar all have high levels of species richness. This thesis shows that Korthalsella
has high levels of regional endemism and has widespread parallelism and supports the
biogeographic model of speciation, whereas, the traditional sections based on
morphology are not supported.
Korthalsella is represented in New Zealand by a monophyletic clade of three
species K. clavata (Kirk) Cheeseman, K. lindsayi (Oliver ex J. D. Hooker) Engl., and K.
salicornioides (A. Cunningham) Tiegh. Korthalsella clavata and K. lindsayi are both
generalists with relatively broad host ranges whereas K. salicornioides is a specialist
species with most host records from two myrtaceous genera Kunzea Rchb. (kanuka) and
Leptospermum J. R. Forst & G. Forst (manuka). Cross-infection experiments in
Korthalsella salicornioides indicate the presence of putative Kunzea- and
Leptospermum-specific races with better success rates of seedling survival when
maternal and recipient hosts were the same. However, genetic data based on nuclear
internal transcribed spacer (ITS) and chloroplast trnQ-rps16 spacer sequences does not
support the presence of host related variability and the within-species genetic structure
appears to be geographic rather than host-based. My study shows that both cpDNA
haplotypes and ITS sequence types are shared between K. clavata and K. lindsayi,
which possiby is an outcome of hybridisation and introgression between the two
species. Korthalsella salicornioides is an ambophilous species relying both on insects
and on wind for effective pollination, whereas K. lindsayi is an anemophilous species.
This study confirms the presence of explosive seed discharge in both species with
dispersal distances ranging up to 4 and 7 m in K. lindsayi and K. salicornioides,
respectively. However, dispersal distances of around 1 m are more typical. This study
also describes the first account of clonal propagation by means of proliferation of
endophyte and formation of adventitious sprouts in these species.
Several new natural enemies specialising on New Zealand Korthalsella were
discovered - two specialist armoured scales (Leucaspis albotecta Henderson and L.
trilobata Henderson), a felt scale (Eriococcus korthalsellae Henderson), and two
pathogenic ascomycetes Guignardia korthalsellae Sultan, Johnston, Park & Robertson
and Rosenscheldiella korthalsellae Sultan, Johnston, Park & Robertson. Other natural
enemies include a specialist gall mite Aceria korelli Manson, whereas generalists
include native and adventive scale insects and generalist Lepidoptera.
Demographic study of several populations revealed that all species have high
growth rates and high ramet turnover. Korthalsella salicornioides and K. clavata had
relatively stable recruitment rates in all size/stage classes whereas K. lindsayi
populations were apparently declining at the two study sites.