Morphological and genetic variation within Metrosideros polymorpha (Myrtaceae) on Hawai'i

The highly polymorphic taxon Metrosideros polymorpha ('ohi'a) is the most abundant endemic tree in Hawai'i, occupying a wide but fragmented range of habitats across Federal, State, and privately managed lands. Morphological character states of 342 herbarium specimens from the island of Hawai'i distributed the five recognised varieties in ordinal space, but intermediate phenotypes were prevalent. Morphological and random amplified polymorphic DNA (RAPD) analyses were undertaken for 10 individuals at 3 sites on Hawai'i. Individuals at a high-elevation dry site and mid-elevation dry site had smaller, pubescent leaves with a higher leaf mass per area and nitrogen content than individuals at a moist mid-elevation site. While the populations were separated in ordinal space, taxonomic varieties overlapped. The high degree of overlap between the taxonomic varieties, based on genetic and morphological characteristics, does not support the current varietal subdivision of Metrosideros polymorpha on Hawai'i.