A preliminary investigation of umbellate inflorescences in Vallisneria americana populations of Central Florida

Abstract

Vallisneria americana typically produces solitary pistillate inflorescences; however, unusual umbellate flowers have been observed in sub-tropical populations and are reported as rare. There are multiple hypotheses regarding the origin or cause of umbellate inflorescences—they may be relics of ancestral stocks surviving through asexual reproduction, heritable traits worthy of taxonomic recognition, or teratological specimens resulting from injury during flower formation. Through surveys of Vallisneria populations in four lakes in Central Florida, USA, we show these umbellate flowers are broadly distributed and we document their physical and reproductive traits, contrasted with solitary capsules (capsule number, capsule length and width, seed number, germination). Umbellate inflorescences were found frequently across space and time—capsules were found in three of four lakes, 40–80 % of the times flowering was observed. Umbellate inflorescences produced fewer seeds than solitary capsules, despite having 2–33 capsules per inflorescence. Seeds from umbellate capsules were viable, but germination occurred more slowly and at a lower percentage than seeds from solitary capsules. Nematodes were not detected within sampled inflorescences. Chironomid larvae were detected at a high rate (75–80 %) in umbellate capsules from two of three lakes but were not found on solitary capsules, suggesting they may be a possible cause for teratological growth. We conclude umbellate inflorescences are broadly distributed in Central Florida lakes and, while not sterile, they may have reproductive costs. Further study is needed to fully evaluate the cause of umbellate formation, population-level effects, and their range within Vallisneria americana.