Water plant maintenance

As most people know, plants absorb CO2 from the air and use it as a carbon source for building stems, leaves, and almost all of the other carbon-based molecules in the plant.  Plants also absorb oxygen from the air to produce energy and absorb water through their roots from moisture in the soil. It is important to allow enough air to get to plant roots. Too much water will drown the roots and starve the plant of oxygen. So it is curious to discover plants that have evolved to prefer their roots to be immersed in water. How do they survive? 

Today's assignment was to prune and clean some of the water plants in the tanks of the collection room #3, representing a subtropical climate. To address the question of how plants survive with very wet roots, I'll highlight two plants with different adaptations to wet feet.

Most of these plants in the two tanks of the subtropical room C3 have finished growing for the year and have entered domancy until spring. Winter is a good time to clean out the dead growth, repot overgrown plants, and control pests that may have invaded them. The two plants I'd like to highlight are the umbrella sedge, and the carnivorous crimson pitcher plant.

Water plants in the Collection room C3. Umbrella sedge in the mid-ground (Cyperus alternifolius)

Umbrella sedge

The umbrella sedge (Cyperus alternifolius) is one of many aquatic species in the large Cyperus family. It features a tall stem crowned by a radial array of leaflets (bracts) which resemble the spokes of an umbrella. Originally from Madagascar, it has become naturalized in many parts of the world. C. alternifolius has an extensive system of roots and rhizomes which help to anchor the plant in the water. The Cyperus genus has structural adaptations to trap air into special spaces in the stems and rhizomes (modified stems) allowing the use of more oxygen from the part of the plant above the water level rather than from the roots.

Today, I noticed the only pot of C. alternifolius in the collection had grown a root ball so large that it was breaking apart the plastic pot. I removed the pot and split the root into two parts; now there are two pots of the plant.

Crimson pitcher plant

Sarracenia leucophylla (the crimson pitcher plant), endemic to the southeastern areas of North America. This plant has evolved in wet boggy soils and marshes. The root system consists of rhizomes from which shallow roots arise. Rather than requiring nutrients to come from roots under water, the plant is carnivorous, and gets much of its nutrition from the insects it digests in its tall trap. The traps are modified leaves which arise from very short stems near the roots. In the spring, the plant sends up orchid-like flowers on separate spikes. There are several other unrelated plant species which, rather than roots, have evolved carnivorous traps of various designs which nourish the plant in very wet or nutrient poor soils.

The pitcher plants did not need repotting, just a bit of pruning back dead leaves and removing mealybug pests from the leaves and exposed parts of the roots.

Carnivorous Sarracenia leucophylla (crimson pitcher plant)