DUCK WEED
by Emma Reid
Just floating on top of the water in our swamps is a large yet very small, diverse botanical world to discover. Our smallest native plant floating communities are called the Lemanceae.
There are five genera, and despite all the local names, each genus has its own official common name:
• Lemna – duckweed – one root per frond
• Spirodela – duckmeat – two roots per frond
• Landoltia – dotted duckmeat – two to five roots per frond
• Wolffiella – mud midget – flat, often spiraled, without roots
• Wolffia – watermeal – round, oval, or elliptical, without roots; the smallest form
Since they are so small, duckweed prefers water that is either still or slowly flowing in ponds, lakes, canals, and bayous. All float at or near the surface, taking advantage of air sacs called aerenchyma. They may be found mixed in with other plants in otherwise open water, or they may reproduce rapidly and cover the surface, with one or a combination of species and genera. They typically are one plant thick on the surface, but winds may push them into thick piles at pond margins. Eventually, these will either sink or spread back out to a thin layer. They may live on moist soils if forced off the water surface by a boat wake or storm.
Lemnaceae are flowering plants. In fact, Wolffia is the smallest flowering plant in the world and produces the smallest fruit. They have simple inflorescences which extend from a cavity in the surface of the frond and consist of one or two staminate flowers and one pistillate flower. They rarely set seeds for some reason. When they do, each fruit, depending on the species, contains 1-5 seeds. The seeds have no flotation, so they sink to the bottom.
Typically, they reproduce asexually. The “mother” frond begins to bud from a meristematic-zone (a place in plants where undifferentiated cells are found and growth takes place). The “daughter” frond exits laterally from a pouch and remains appended to the mother by a connecting stype until it is mature, at which time it breaks away. By this time, the former daughter has probably already produced its own daughter fronds.
This process is rapid. Various species can double their coverage of habitat every two days. One species of Wolffia in India can bud a new daughter frond every 30 hours, meaning that one mature frond can, in four months time, produce offspring (with each offspring producing offspring) that are equal in volume to that of the earth! Thankfully, this hasn’t happened.