Phenology of fruit development and abortion in sawgrass, Cladium jamaicense, and its consequences for seed bank viability

• Sawgrass aborts 30–50% of fruits late in development but before fruit drop.
• Unaborted and aborted sawgrass fruits have a hard endocarp and form persistent fruits.
• Persistent aborted fruits are shed into the seed bank and affect seed bank viability.
• Seed bank viability was accurately modeled with measured rates of aborted fruit input.

The common marsh macrophyte Cladium jamaicense (sawgrass) has high levels of fruit abortion. We investigated the phenology of post-fertilization fruit development and of fruit drop in southern Florida, USA, to determine the timing of fruit abortion in relation to fruit shedding. Fruits at two sites were harvested at 2-week intervals, weighed individually and examined for potential viability (PV) to document changes in fruit biomass, morphology, and abortion rate. Fruits shed into 1/4 m2 traps placed in sawgrass patches at two sites were counted and assayed for PV every one or two weeks in summer 2009 and 2010. Sawgrass sheds fruits from mid-July to September with peak fruit drop in late July to mid-August, 2–2.5 months after flowering. Sawgrass fruits had high rates of abortion that differed among plants and between sites and increased from mid-July through August. One-third to one-half of all fruits shed by a plant over the summer were aborted. Sawgrass plants had late fruit abortion that occurred prior to shedding but after investment in fruit development, producing persistent aborted fruits. A model for the effect of these fruits on seed bank viability predicted levels of 2% seed viability in the seed bank for 50% fruit abortion, similar to values for seed bank germination from the literature. The low percent of viable sawgrass seeds reported here provides a baseline population parameter for Everglades and other Caribbean marsh restoration and indicates the need to determine the input of viable fruits when studying seed banks and/or germination.