My Green Wet Thumb: The Sensitive By Derek P.S. Tustin

For all I truly enjoy keeping fish, I find that it is not the most tactile of hob- bies. I have two wonderful dogs and part of the fulfillment of each day is the necessity of petting them, for they demand and enjoy the physical contact between us. Cats demand the same touching (although more on their terms than ours), and there is a degree of tactile interaction with the keeping of both birds and reptiles. But for the most part, if we handle the fish we keep then we have done something wrong. I’ve handled fish after they have leapt out of the tank (my fault for not securing the lid), but other than once per- forming minor surgery on a pleco (the removal of an odd growth from its dor- sal fin), the only time I’ve touched my fish is to remove their bodies after they have died.

The care and keeping of aquatic is a bit more tactile given that han- dling plants won’t cause them too much stress. Planting, pruning, and re- planting all require that the plants be handled for a short period of time, and there is some knowledge that can be gleaned through handling plants. For instance, did you know that one way to discern between a in the Sagit- taria versus a plant in the Vallisneria genus is to feel the edge of the ? If you can feel serrations, or small jagged tooth like ridges (actually called denticles), then the plant is a Vallisneria. If they are absent, the plant will be a Sagittaria.

But for the most part a plant, unlike a fish, is unresponsive to touch. But like everything else in our hobby, there is an exception to the rule…

1710 saw the birth of João de Loureiro (sometimes Joannis de Loureiro) in Lisbon, Portugal. Most of you have probably never heard of him, but he was admitted to the Jesuit Order and sent to what was then known as “The Ori- ent”. He spent three years in Goa (an area of West India), four years in Ma- cao (a region in China), and in 1742 was sent on a special mission to Cochinchina (which is essentially the southern third of what today is Vi- etnam, and is entirely south of what today is Cambodia). He came to find that missionary work was not his strength and became a mathematician and naturalist in the service of Nguyen Phuc Khoat (aka Vo Vuong, the Martial Prince), the King of Cochinchina. As a member of the Jesuit Order, he had some knowledge of medicine and this made him popular with the people of Cochinchina. However, he did not have access to European medicines, so he came to depend on native medicines. To enhance his knowledge on this

14 The Tropical News subject, he began to study and gather bo- tanical specimens of local flora. He even- tually returned to Por- tugal in 1781 and in 1790, the year pre- ceding his passing, he published the Flora Cochinchinensis, a listing of 1,257 plants and the first detailed examination of flora found in the region, completely based on his own gathering of flora from that region.

Contained within the pages of Flora Cochinchinensis was a description of Neptunia prostrata, the first species described in the genus. However, de Loureiro was unaware that another botanist, Jean-Baptiste Lamarck, had described the same species as Mimosa prostrata.

The Mimosa genus contains in excess of 400 species of terrestrial shrubs and herbs, but one, Mimosa pudica, is commonly known as the Sensitive Plant or the Touch-Me-Not. When the plant is disturbed, be it by wind, water or touch, the leaves rapidly fold inward, appearing to close in on themselves. Neptunia prostrata, what we know today as the Water Sensitive Plant, dis- played the same behavior, and Jean-Baptiste Lamarck placed the Water Sensitive Plant in the same genus as the terrestrial Sensitive Plant. Howev- er, it was later determined that although they exhibit the same behavior, they were not in the same genus, and the name Neptunia, which in fact had been chosen by João de Loureiro in recognition of the plant’s aquatic habitat, was recognized as the correct genus name for all Water Sensitive Plants.

The name Neptunia prostrata was later replaced with Neptunia oleracea, the name by which the plant is known today. The genus currently has 13 recog- nized species. Interestingly enough, the binomial name most often attached to the Water Sensitive Plant is Neptunia aquatica, a name which has no sci- entific validity, and likely was created for marketing purposes. The correct name, Neptunia oleracea, is composed of the genus name of Neptunia, re- ferring to the plant being found in an aquatic environment, and oleracea, which is word derived from Latin origins meaning “of cultivation, aromatic, vegetable” or “pot-herb”.

As can be surmised from the Latin meaning of the species name, the plant

The Sacramento Aquarium Society 15 is actually edible. It is a common ingredient in , and both the leaves and young shoots have a nutty cabbage like flavor. It can either be eaten raw or cooked, usually being added to soups. In addition to being used as a food source, it has reported medicinal uses, with the roots being used to treat necrosis of the bones of the hard palate and nose, the juice of the stem being squeezed into the ear to cure earaches, and an infusion of the roots being mixed with rice flour and rubbed over the body to reduce fe- ver.

For aquarists, the best use of this plant is in the pond. It can be bought ei- ther bare-root or potted, in both cases usually a stalk between 5 – 8” (12.5 – 20 cm) in length. The bare-rooted plant is often recommended as a floating plant in the pond, but in my experience better growth is achieved when grown as a potted plant. If placed in a small pot with common aquatic soil, it will grow to and then across the water surface, capable of reaching lengths in excess of 60” or 5’ (1.5 meters). The stalks will only very rarely branch, and best growth is achieved with the use of fertilization, preferably via root tabs.

If planted on the edge of a pond (with the base submerged up to 6” [15 cm]), you will find that it not only grows across the water as a floating plant, but will also grow across the terrestrial surface surrounding the pond. Interestingly, when Neptunia oleracea grows across a terrestrial surface, it will show differ- ent characteristics than one which grows across an aquatic surface. When grown as a floating plant, the stem of the plant will develop a white, spongy tissue called “aerenchyma”. Aerenchyma refers to spaces or voids in the stem that allow the exchange of gases between the roots, stem and leaves of the plant, and, as they are basically filled with air, will assist the plant in floating.

While the plant can survive lower temperatures (having survived in my pond at temperatures as low as 57oF [14oC]), it is best grown with water tempera- tures in excess of 68oF (20oC). It should be placed in full sun or partial shade. Saline conditions, either through brackish water or saline soil, should be avoided as such conditions will adversely affect the growth of the plant.

The leaves, which have a fern-like appearance, will form on alternating sides of the stalk as it grows out across either the land or the water, and it is the behavior of the leaves that is the most interesting thing about this plant. Like Mimosa pudica, the leaves of the Water Sensitive Plant truly are sensitive. They display both nyctinastic and seismonastic movement. Nyctinastic movement refers to the leaves folding and drooping at night, and seismonas- tic movement refers to the leaves folding and drooping due to contact or agi- tation. They will once again open or unfurl in the morning or, if disturbed and as a result folding up during the day, will once again unfurl within a matter of minutes.

16 The Tropical News

From mid-summer until the earliest frost, the plant will produce small pea- shaped puffy yellow flowers. Beneath these yellow flowers (which are the female flowers), small barely noticeable male flowers are produced. From the combination of these two seeds may be produced. The more common propagation method is by division and replanting of the stalk of the plant.

In warm climates, the plant can be grown in ponds year-round (although they do have the potential to become invasive), and in cooler climates can be overwintered in a well-lit warm aquarium.

They are an excellent addition to any pond, being very easy to grow, provid- ing excellent surface coverage for koi and other pond fish, and will assist in algae control.

In addition to Neptunia oleracea, there is another similar plant that may be sold under the name of Water Sensitive Plant. It is actually Aeschynomene fluitans, or the Giant Water Sensitive Plant. With the exception of its poten- tial size (of both leaves and spread) and speed of growth, it is almost identi- cal in all aspects to Neptunia oleracea.

So there you have it. I know we’ve all been told not to poke things, but in this case give it a try. It is actually very interesting to observe, and the plant is an excellent and interesting addition to any pond.

Neptunia oleracea

Latin Name: Neptunia oleracea Common Names: Water Sensitive Plant Water Mimosa Garden Puff Height: 7.5 – 12.5 cm (3” – 5“) Planting Depth: 2.5 – 15 cm (1” – 6”) Light: Full sun to part shade Temperature: 20 – 30oC (68 – 86oF) Growth: Fast Difficulty: Easy Blooming Season: Summer until frost Bloom Colour: Yellow Origins: Southeast Asia

Image from: http://www.missouribotanicalgarden.org/Portals/0/PlantFinder/ low/D664-0722091gk.jpg

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