Of all of the genera of plants available to aquatic plant enthusiasts, perhaps none is more diverse in form and habit than Ludwigia. Wherever you live and whatever your circumstance, there is probably at least one member of this genus that will do well in your water garden. Most of them are frost-tolerant, drought-resistant and otherwise capable of surviving almost anything that comes their way.
Ludwigia is a part of the family Onagraceae (which also includes Oenothera and Fuchsia), and includes approximately 75 species of herbaceous to semi-woody plants. It enjoys a cosmopolitan distribution, with most species occurring naturally in warm regions of the Americas. In North America, several species can be found either broadly distributed or in tightly circum- scribed regions from northeast Mexico and Texas to New Jersey. Many species have been introduced to areas far afield from their native ground, however, and so have become naturalized in many places. Only a handful of species are commonly used in the water gardening world, and most of those are in aquaria.
Some confusion exists in the nomenclature within the genus. With a synonymic genus, Jusseia, and the close similarity of form between some species, confusion is bound to creep in at some point. For instance, what I have as L. repens, and have unquestioningly kept under that name for more than 40 years, turns out under closer scrutiny to be a form of L. peploides. It used to be called Jusseia repens f. peploides (hence the confusion), and what is kept as L. peploides is actually L. peploides peploides. There is a third form that produces red stems and narrower leaves and has an indentation on the outer margins of the petals. Furthermore, the actual L. repens is almost indistinguishable from L. palustris, which is completely different from my former L. repens. Also, what I got from a noted expert as L. peruensis, a tall bog plant, has a rival for that name in the aquarium plant industry that is utterly different from my plant.
The genus is large, interesting and, in most cases, easy to grow. Based upon growth habit, it is possible to divide it into three large groups.
First, there are those species that will persist in a submersed condition but will produce floating olonies of tangled stems and leaves, or that will emerge and grow prostrate along embankments when forced to and remain strictly herbaceous. In form, they range from creeping plants with acuminate, linear leaves (L. arcuata); to plants with ovate to rhomboid leaves (L. palustris, L. repens) that might be small, and dark green, as occur when they are on drying mud, or about an inch across and bright red, as when they are underwater in full sun. All of these species — and there are several — can be used in planted aquaria to good effect.
Among the more strictly aquatic species is the very unusual Brazilian native, L. sedioides (Mosaic Plant), which, when it is happy, produces a striking pattern of floating rosettes of small, multi-colored leaves with notched edges, accented with bright yellow flowers. The neat and orderly appearance of the surface display conceals a tangle of roots, stems and old leaves just beneath the surface that provide a great habitat for small creatures. Of all of the species within this genus that I have grown, this one is the most exacting in its requirements and has proven to be the most difficult to overwinter. Nevertheless, the display in summer can be well worth the effort that is necessary to keep it alive in the greenhouse.
The second grouping includes those plants that will grow underwater for short periods, but which do not produce submersed leaves that are substantially different from the emersed ones. They prefer to be in the air, and when they are, they float across open water or climb among reeds and other marginal plants that will support their weight. The floating stems frequently produce swollen areas along their length that serve as floatation devices. The leaves are ovate to lanceolate and prominently veined, and the stems become semi-woody. Examples include L. hexapetala and the various forms of L. peploides. These plants can form low- growing masses of tangled stems that make passage nearly impossible, with each year’s growth piling onto that of the previous year unless the keeper thins it out every fall or in late winter, when it begins to regrow. There are at least two forms of L. peploides: one with inch-long leaves and flowers three quarters of an inch in diameter, which is better for small ponds; and the larger one, L. peploides peploides, which produces much larger leaves and flowers and is suitable only for large ponds. Because of the copious roots that they produce, all of the plants in this group are excellent adjuncts to biological filtration while they are actively growing.
And finally, there are those plants that grow erect, strictly emersed, and become at least semi-woody. The larger species, such as the robust L. peruensis or the elegant L. longifolia, grow to several feet tall and can produce wild messes of tangled stems that reach 10 or 12 feet in length. Where they touch water, they root, and so form huge, nearly impassable colonies along river banks. So why would a person want one? Because they are handsome, they are floriferous, they mix well with other species and they respond very well to pruning. A person growing one in his pond might allow it to reach any height that he wants. I allow them to get to a size that is proportional to the pond and cut them at will above that line. In the fall, I knock them down to about 18 inches tall and allow them to start over in the spring. In mild winters here in Southern California, they can continue to grow almost unabated through the “cold” months. One drawback to their use is that they produce millions of dust-like seeds that will germinate in wet lawns and bog planters, but these pull easily when they are young and need not become too much of an issue. In some cases they look good within the landscape. So, whether you are an aquarist or a pond keeper, the genus Ludwigia should not be overlooked when selecting species to include in your plantings. Their versatility and attractiveness fit well into most water gardens, and the bright yellow flowers accent the scene well. I use them as I can and would encourage people to consider the genus when planning what to include in their aquaria and bog gardens.