Facilitated fecundity in sand flax: Pollination in an endangered herb of pine rocklands

Abstract

Reproductive success in flowering plants depends on floral biology, breeding system, and availability of compatible mates and pollinators. Here, we examine the pollination biology of Linum arenicola (Small) H.J.P Winkler (Linaceae), sand flax, a federally endangered herb of pine rocklands in the Lower Florida Keys (USA). We observed the timing of floral anthesis, fruiting, florivory, and frequency of flower visits by insects. We compared fruiting in flowers that were open-pollinated, bagged to exclude floral visitors, and self-pollinated by hand to determine whether pollinator visits enhance or are necessary for reproduction. Fruit set was equally high between flowers open to pollinators and those that were hand-pollinated, but both were significantly higher compared to flowers from which pollinators were excluded. We observed that the wilting of petals late in the day in unvisited flowers often initiates self-pollination, but flowers are frequently visited by small bees and flies earlier in the day, suggesting that early day visits by those insects increase pollen deposition and potential for outcrossing. Despite high fruit set from autonomous self-pollination and occasional flower visitation, sexual reproduction is limited by herbivores: nearly half of all flowers produced were consumed by Key deer and galling midges. Optimum fruit set is not achieved from autonomous selfing alone, and pollinators play an important role in fruit production of the rare sand flax. Conservation efforts that enhance populations of suitable pollinators could increase the likelihood of fruit set from a diversity of pollen parents in rare plants like the endangered sand flax.