Interspecific Incompatibility Amongst Victorian Species of Amyema (Loranthaceae)

Abstract

Each of the six Amyema species collected in Victoria had a natural distribution and floral phenoiogy that overlapped with at least one of its Victorian congenerics. All of the Amyema spp. were pollinated by the same family of birds (Meliphagidae, honeyeaters) and often by the same species.

All intraspecific cross-pollinations in vitro consistently produced an average of more than five pollen tubes per style which grew more than 0.125 the length of the style within 24 hours. Seventeen of 30 interspecific pollinations in vitro failed to produce pollen tubes in the style over the same time. Only eight of the 30 interspecific crosses attempted produced results competitive with respective intraspecific crosses. The success of the interspecific cross appeared to depend on the breeding system of the species receiving pollen from another. Self-incompatible Amyema pendulum (Sieb. ex Spreng.) Van Tieghem and Amyema miraculosum (Miq.) Van Tieghem repeatedly failed to accept the pollen of all the other species. Seif- compatible Amyema preisii (Miq.) Van Tieghem and Amyema quandang (Lindl.) Van Tieghem showed good to excellent interspecific pollen tube penetration of stylar tissue. Partially self-compatible Amyema linophyllum (Fenzl) Van Tieghem and Amyema miquelii (Lehm. ex Miq.) Van Tieghem showed results intermediate between self-compatible and self-incompatible taxa.

Geographic and floral phenological barriers contribute partially to interspecific isolation as intercompatible species may have regionally different flowering seasons and distributions. F, hybrids recorded in southern Australia show extremely low rates of pollen viability and seed production. There is no current evidence that introgression occurs.