Reproductive ecology of Sandhills pyxie-moss Pyxidanthera barbulata (Michaux) var. brevifolia (B.W. Wells) Ahles

Background/Question/Methods Conserving rare endemic plants often requires an understanding of their reproductive biology. We investigated pollination ecology, breeding system, and seed germination in Pyxidanthera barbulata Michaux var. brevifolia (B.W. Wells) Ahles (Sandhills pyxie-moss), an endemic taxa of the Sandhills region of North and South Carolina.

Results/Conclusions At study sites on Fort Bragg, North Carolina, Sandhills pyxie-moss plants were found to be self-incompatible and dependant upon insects from the Orders Hymenoptera and Diptera for seed capsule production. Ants, in addition to winged insects, were found to be important pollinators. Prenolepis imparis (Say) (winter honey ant) was the most abundant and temporally invariant pollinator, observed active above ground during the winter and early spring when Sandhills pyxie-moss flowers and when most winged insect species were inactive. An assessment of plant characteristics suggests that although Sandhills pyxie-moss is pollinated by several different insect groups, it predominantly typifies an ant pollination syndrome. The species exhibits with varying stricture seven of the ten ant pollination syndrome traits Hickman (1974) proposed, based on plant and pollinator energetics, including:  1) occurs in hot and dry habitats with high levels of ant activity, 2) nectaries are readily accessible to small, short-tongued insects, 3) plants are short or prostrate, 4) populations are dense and/or have low plant species diversity, 5) synchronously blooming flowers should be few per plant, however, high densities, reduced height and self-incompatibility or dioecy may allow more flowers per plant, 6) on matted plants, the flowers occur on the mat surface, and 7) flowers must be small. Lab and field germination rates were markedly low, suggesting that maintaining existing Sandhills pyxie-moss colonies should be an important component of any successful conservation strategy for the species.