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Propagules (stem cuttings) of alligatorweed [Alternanthera philoxeroides (Mart.) Griseb.] were subjected to various treatments of submergence, emergence, light, dark, and oxygen to relate hypoxia to the suppression of alligatorweed growth by dark submergence. In the dark, submergence completely inhibited alligatorweed growth. A nitrogen atmosphere inhibited growth from emersed propagules in the dark. The suspension of growth by dark submergence was relieved by light (40 μ einsteins/m2× s photo‐synthetically active radiation), emergence (whereby air is transported to underwater nodes via the aerenchyma), or exposure to 100 mg · l‐1 of hydrogen peroxide solution renewed at 48‐h intervals. Suspension of growth by a nitrogen atmosphere was relieved by inclusion of 16% oxygen in the ambient atmosphere. Dark to light transfers showed that the suspension of growth was immediately relieved if the requisite conditions were restored; this phenomenon, as described, thus appears to be hypoxic quiescence. The suppression of growth of two other amphibious species, mild smartweed (Polygonum hydropiperoides Michx.) and creeping water‐primrose (Jussiaea repens L. var. glabrescens Ktze.), by dark submergence suggests that hypoxic quiescence may be a factor in the life history of amphibious species other than alligatorweed.

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