Story: Evolution of plants and animals
Page 6 – Plants in a mild climate
New Zealand has mild winters, moderately warm summers, and well-distributed rainfall. The adaptations of plants and animals in more seasonal climates are absent. New Zealand's indigenous plants tend to be sensitive to frost and cold. Even some alpine plants such as New Zealand's Veronica (formerly Hebe) – popular in British gardens – cannot survive a cold British winter. Only a few native trees and shrubs lose their leaves in winter, and adaptations protecting plants from frost (such as hard cases covering winter buds) are uncommon.
New Zealand plants are mainly evergreen perennials. Annual herbs, or those that die back in winter and store their bulbs underground to re-sprout in spring, are uncommon. Similarly, few insects undergo diapause – a state of suspended development during unfavourable periods, which is a common adaptation in insects in highly seasonal climates.
Naturally-caused fires are rare in New Zealand, and few trees and shrubs have the defences common in fire-prone areas, such as thick bark, buds below the bark, large storage roots, and fire-promoted release of seeds. The woody plants that do have these features are usually of Australian origin (mānuka), or are closely related to Australian species (matagouri).
Herbs to bushes
Dense, evergreen forests and lack of natural grasslands below the treeline are probably the reason for ‘insular woodiness’ – where herbaceous ancestors rapidly evolve into woody descendants. New Zealand has woody members of the daisy family, the carrot family and the plantain family, which are often herbaceous in temperate continental regions.
New Zealand’s largest flowering plant genus is Veronica, formerly Hebe, with 121 native species (hebes and their relatives). These plants, which range from small trees to alpine cushion plants and a tiny lake-shore herb, diversified from a single ancestor during the last 10 million years. Their ancestor was probably a low-growing northern hemisphere plant similar to the common speedwell (Veronica arvensis). It’s thought the evolution of woody hebes like Veronica stricta was aided by the familiar enclosed leaf buds, which give protection to the delicate stem tips.