Genetic and morphological evidence for localised interspecific gene flow in Phormium (Hemerocallidaceae)

Abstract

Gene flow between two species of Phormium, P. tenax and P. cookianum, was investigated by analysis of morphology, AFLP profiles, and chloroplast simple sequence repeats (cpSSRs). We examined 44 wild samples of Phormium, focusing on Okiwi Bay (Marlborough, New Zealand), where the two species grow in close proximity. Two genetic groups corresponding with P. tenax and P. cookianum are evident in analyses of AFLP profiles from Okiwi Bay. The profiles of Okiwi Bay plants were also compared with profiles from three hypothetically pure P. cookianum populations from Marlborough, and a representative sample of P. tenax combined from sites throughout New Zealand. Bayesian analysis of genetic admixture suggests that all of the plants resembling P. tenax and most of the plants resembling P. cookianum sampled from Okiwi Bay are admixed (i.e., of hybrid origin). Neighbour Net and principal component analyses reveal that P. cookianum and P. tenax from Okiwi Bay are genetically intermediate between “pure” populations of the species. Further, all of the Okiwi Bay samples share the same chloroplast haplotype. Analysis of morphological characters comparing a small number of Okiwi Bay P. tenax plants to selected P tenax plants from throughout New Zealand under common garden conditions confirm that the Okiwi Bay population includes plants with unusually small stature and fruit characters approaching P cookianum. These results support a hypothesis of local introgression between P. tenax and P. cookianum.