Potential and realized rates of vegetative reproduction in Spirodela polyrhiza, Lemna minor, and Wolffia borealis

Abstract

The rate of vegetative propagule development was estimated in three duckweed (Lemnaceae) species, Spirodela polyrhiza, Lemna minor, and Wolffia borealis, by measuring the number of daughter fronds produced over the life span of mother fronds. Under the same constant environmental conditions, plants of L. minor lived the longest (31.3 days) and produced the most daughter fronds (14.0), yet W. borealis had the highest reproduction rate (0.62 fronds per day). This translates to a higher rate of population growth for W. borealis. Plants of S. polyrhiza had the shortest life span (12.1 days), produced the least number of daughter fronds (1.1), and thus had the lowest frond production rate (0.08 fronds per day). When S. polyrhiza was experimentally induced to release daughter fronds at maturity, and not well past maturity (which is usually the case), mother fronds produced three times more daughter fronds with no effect on their longevity. Presumably different retention times are associated with different costs and benefits, however frond longevity appears unrelated to retention time. Vegetative propagule production in the Lemnaceae forms a continuum from Wolffia, which develops relatively small (0.5–1.5 mm) and numerous propagules that are released before maturity, to Spirodela, which develops fewer yet relatively large propagules (4–12 mm) that are retained well past maturity. The different rates of propagule production likely represent different reproduction strategies, from an opportunistic strategy (i.e. Wolffia), to a strategy of increased competitive ability (i.e. Spirodela).