Variation of inherent seed capsule splitting in populations of Leptospermum scoparium (Myrtaceae) in New Zealand

Abstract

Variation in the splitting of seed capsules was observed for 61 populations of Leptospermum scoparium from a wide latitudinal range in New Zealand raised from two sowings and grown in uniform environments. Variation ranged from populations for which capsules of all shrubs had split and shed seed within a year of their formation to those for which all shrubs had serotinous capsules that remained intact and retained seed for a longer period. There was a significant latitudinal gradient in this variation with northern populations being strongly serotinous. The variation of capsule splitting was independent of the time taken from sowing to the first flowering of plants. These results are discussed with regard to the ecological adaptation of L. scoparium to various habitat disturbance factors. It is concluded that the variation observed is consistent with the opinion that the New Zealand flora generally lacks fire adaptation but, since human settlement, rapid selection of fire‐adapted genotypes of L. scoparium has occurred in populations that are seral in secondary succession to forest.

Keywords:

• Leptospermum scoparium
• manuka
• capsule splitting
• serotiny
• flowering phenology
• essential oil
• fire adaptation
• vegetation disturbance
• New Zealand