Bruguiera Species in Hawai'i: Systematic Considerations and Ecological Implications

Abstract

At least two mangrove tree species in the genus Bruguiera were introduced into Hawai'i from the Philippines in 1922. The two are described in the most current manual on the flora of Hawai'i as B. gymnorrhiza (L.) Lamk. and B. parviflora (Roxb.) W. & A. ex. Griff. There has, however, been some confusion since its introduction as to the identity of what is currently known as B. gymnorrhiza. Early Hawaiian flora manuals (1948 and earlier) and ecological research reports up until at least 1972 referred to the species as B. sexangula (Lour.) Poir. Flora manuals published after 1948 and recent ecological papers describe the species as B. gymnorrhiza. The reason for the change appears to have been based strictly on an assessment of flower color. In this study we collected specimens of Bruguiera from Hawai'i and known samples of B. sexangula, B. gymnorrhiza, and B. exaristata C. G. Rogers from Australia or Micronesia. Based on a multivariate comparison of flower and hypocotyl morphology of this material, an assessment of other diagnostic attributes, and amplified fragment length polymorphism (AFLP) mapping, we conclude that the primary, and perhaps only, Bruguiera species present in Hawai'i is B. sexangula. We argue that the current distribution of Bruguiera in Hawai'i fits the pattern that might be expected of B. sexangula, which is less salt tolerant than B. gymnorrhiza. We also conclude that sufficient regional variation occurs to warrant morphological and genetic comparisons of the three species across their whole geographic range.