Reproductive biology of Euonymus americanus (Celastraceae): Pollination by ants and cockroaches.

Euonymus americanus is a common understory shrub in mesic deciduous forests of eastern North America. Its inconspicuous greenish-white flowers appear in late April and May and are regularly visited by several species of ants and, by night, a species of cockroach. Because the species is self-compatible, these pollinators need not move between plants to effect fertilization and fruit-set. Flowers last for three days and are strongly protandrous with little if any overlap of male and female function. Based on a survey of five years of reports on iNaturalist in Georgia, Prenolepis imparis is the most commonly observed ant, followed by Camponotus pennsylvanicus and Crematogaster lineolata, though Camponotus castaneus was more common than the latter two species at our study sites. Each of these species was found to carry many viable pollen grains, as was a species of cockroach (Cariblatta lutea). Exclusion of ants from flowers resulted in near-zero fruit-set. Nevertheless, addition of pollen increased fruit-set significantly over open-pollinated levels, indicating pollen limitation. The upper limit in terms of potential seeds per fruit is 30, representing six seeds in each of the five locules of a mature capsule, but the average number of seeds per capsule was only 12. Seed viability was high, exceeding 95%. [ABSTRACT FROM AUTHOR]