W Harris; RE Beever; SL Parkes; BM Smallfield; R-A Anderson; S Scheele
Progeny of 28 wild populations of Cordyline australis (cabbage tree, ti kouka) from a 12° latitudinal range in New Zealand grown under uniform garden conditions at Mt Albert, Auckland (36°53´S, 174°43´E), Lincoln, Canterbury (43°38´S, 172°29´E), and Invermay, Otago (45°51´S, 170°23´E), differed in the number of years they took to flower for the first time (years to first flowering, YFF) and in the date their flowers first opened each season (first flowering date, FFD). At Auckland population YFF was unrelated to latitude of origin, but at Lincoln and, especially, Invermay, there was a well-defined increase in YFF the further north the latitude of origin of populations. FFDs were delayed progressively from Auckland to Invermay and showed a well-defined pattern of being earlier for southern populations and a weaker trend for earlier flowering with increased altitude of origin. In 2002 and 2003 population FFDs extended over 16–19 weeks at Auckland and narrowed to 2–4 weeks at Invermay. Environmental factors determining floral competence and initiation are considered together with selection pressures that underlie the genotypic variation of flowering phenology of C. australis. Applications of the results to the principle of using locally sourced plants for restoring native vegetation and for the purpose of monitoring the ecological consequences of climate change are discussed.