Unconventional Germination in Terrestrial Plants: A Counterintuitive Case in Desiccation-Sensitive (Clusiaceae) Seeds Showing Seedling Growth Without Roots.

Unconventional germination, wherein shoots emerge and establish true leaves before the root emerges, is only found in Zosteraceae. In , germination proceeds with the primary root emerging, followed by shoot emergence on the opposite side, but before leaf differentiation, adventitious roots emerge at the base of the shoots. However, germination and survival mechanisms in several species are still unclear. We subjected freshly collected seeds to an imbibition test, and germination was evaluated at various temperatures and light conditions. Desiccation sensitivity assessments were made at different stages of drying. The effect of natural drying (ambient storage) on germination was assessed by leaving the seeds outside in natural conditions. Seeds of with a moisture content (MC) of 67% had more than 95% germination only at 25 and 25/30 °C both in light/dark and darkness, but at 25/40 °C only 10% germinated. In 4% of the seeds, germination incepted with primary shoot emergence, and a secondary (adventitious) root emerged just before leaf differentiation. More than 95% of the seeds germinated with only a secondary root and shoot emerging concurrently. Drying fresh seeds above silica gel to 30% MC resulted in complete viability loss. Seeds stored at ambient conditions germinated without external water, and had no primary or secondary root, and the emerging shoot continued to grow into seedlings. A root develops in these seeds only when water becomes available. seeds are desiccation-sensitive and non-dormant. When no external water is available, seeds can germinate with shoots and establish seedlings. This is the first report on germination and successful seedling establishment without roots in .