"Xanthorrhoea
Xanthorrhoeas are endemic to Australia with 28 species and five subspecies currently recognised.
The trunks in some species can grow to 6m. Although mean growth rate is only known for a few
arborescent species and ranges from 0.88–2.6cm per year, individual plants can vary considerably in
growth rate depending on environmental conditions. Cultivated from seed, faster growing
Xanthorrhoea species can develop 10–15cm trunks in 10 to 15 years. In two Xanthorrhoea species
leaves live 2–2.8 and 2–2.5 years respectively. Leaf growth in X. preissii appears to be continuous,
ranging from 0.5–3.2 leaves per day. Inflorescence growth can reduce leaf growth. Growth of
inflorescences can be rapid and up to around 10cm per day. Many Xanthorrhoea species grown from
seed can first flower at 5–6 years of age. Flowering can still occur in Xanthorrhoea estimated to be
300 or more years old. Based on known growth rates, some tall X. preissii are estimated to be 350
years old, while radio carbon dating gave ages up to 600 years."
so who knows???