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.

Vallisneria americana通常产生单生雌蕊花序；然而，在亚热带种群中观察到了不寻常的伞形花，据报道很少见。关于伞形花序的起源或原因有多种假设——它们可能是通过无性繁殖幸存下来的祖先种群的遗物、值得分类学认可的遗传性状，或者是在花形成过程中受伤导致的畸形标本。通过苦草调查在美国佛罗里达州中部四个湖泊的种群中，我们展示了这些伞形花的广泛分布，并记录了它们的物理和繁殖特征，与单蒴果形成对比（蒴果数、蒴果长和宽、种子数、发芽）。伞状花序在空间和时间中经常被发现——在四个湖泊中的三个中发现了蒴果，观察到开花的时间为 40-80%。尽管每个花序有 2-33 个蒴果，但伞形花序产生的种子比单蒴果少。来自伞形蒴果的种子是有活力的，但与来自单蒴果的种子相比，发芽发生得更慢且百分比更低。在采样的花序中未检测到线虫。在来自三个湖泊中的两个的伞形胶囊中检测到摇蚊幼虫的比率很高（75-80％），但在孤立的胶囊中未发现，这表明它们可能是致畸生长的可能原因。我们得出结论，伞形花序广泛分布在佛罗里达州中部的湖泊中，虽然不育，但它们可能具有繁殖成本。需要进一步研究以全面评估伞形体形成的原因、种群水平的影响及其在美国苦草。