The intact germination unit [seed+endocarp, (‘seed’)] of the two species of the Australian endemic genus Stylobasium (Surianaceae, Fabales) is water impermeable. Thus, the seed does not imbibe water or germinate until the integrity of the endocarp, which contains an outer layer of palisade cells, is disrupted. In this study, intact seeds of S. australe and of S. spathulatum, incubated on a moist substrate (for up to 2 years), did not imbibe water, whereas those that were mechanically scarified (both species), or dipped in boiling water for 30 s (S. spathulatum), imbibed and germinated. Thus, seeds of Stylobasium species have physical dormancy (PY). This is the first report of PY in Surianaceae, making it only the sixteenth family of angiosperms (no gymnosperms) in which this class of seed dormancy has been identified.
