Water-impermeable fruits of the parasitic angiosperm Cassytha filiformis (Lauraceae): confirmation of physical dormancy in Magnoliidae and evolutionary considerations

Abstract

Physical dormancy (PY) in seeds or fruits has been reported in 17 angiosperm families but not in basal angiosperms, magnoliids or gymnosperms. Here, we report PY in fruits (germination unit) of Cassytha filiformis, a parasitic species in the magnoliid clade. Moisture content of fruits ranged from 10% to 16%, and the seeds are orthodox (desiccation tolerant). Manually scarified fruits increased in mass >80% during imbibition, whereas untreated fruits increased <16%, via only a few fruits imbibing. Thus, the fruits are water impermeable. Dye did not penetrate the lignified palisade layer in the endocarp. Dye tracking of innately non-dormant fruits suggested that the carpellary micropyle is the water gap in C. filiformis fruits. Manual scarification broke dormancy of most, but not all, C. filiformis fruits. Thus, a high percentage of the germination units have PY and a low percentage PY + physiological dormancy. This is the first verified report of PY in the magnoliids; PY is now known to occur in four of the five major angiosperm clades. The evolutionary aspects of PY in Cassytha, an isolated genus in Lauraceae, are discussed.