LUDWIGIA X LACUSTRIS
Synonyms: Ludwiga brevipes x palustris
Light Needs: Medium
Plant Structure: Stem
Region: North America
Location: Scattered locations from Rhode Island to Georgia
Size: Stem width 2 inches
Growth Rate: Fast
Can Be Grown Emersed: Yes
Ludwigia x lacustris is a relatively recent introduction to the aquarium hobby. A very rare natural hybrid of Ludwigia brevipes and L. palustris, it is found as roughly a dozen widely scattered populations in coastal areas from Rhode Island to Georgia. Curiously, it occurs in several places within the broad range of L. palustris but well outside the rather restricted range of L. brevipes, which occurs mainly in Southeastern Virginia and the Carolinas; the reasons for this are unclear, but it may be because L. brevipes had a much wider distribution in the recent past. Alternatively, it may have been transported to new locations by waterfowl. Where it does occur, it often grows vigorously enough to virtually exclude its parents, a trait commonly shared by other hybrids. It is often equally abundant above and below the water as far down as several feet and is rarely difficult to find. Originally described by Eames in 1933 as Ludwigia lacustris, its hybrid nature was only realized later.
Like L. brevipes, the innermost portions of its leaves are palest, gradually changing from green to orange along the leaf. Unlike L. brevipes, which usually grows as a sort of low hedge, it shares the more upright growth habit of its other parent species. But unlike the more established and faintly similar Ludwigia arcuata x L. repens,, it does not grow at a 45 degree angle. Leaf width and shape are intermediate between both of its parents and in good conditions are roughly diamond-shaped. This plant is quite adaptable and forgiving, but when given strong light, co2 and lots of iron, it takes on a brilliant rust color that is rarely rivaled. It will then achieve its maximum size of perhaps three inches leaf tip to leaf tip.
Undoubtedly, Ludwigia x lacustris is best used as a background plant (or perhaps in the middle area of a very large aquarium). Robust groupings show it to best effect; like closely related Ludwigia species, it does not look quite as good as only a few stems. Its growth can be very vigorous indeed, but fortunately, it does not appear to suffer from pruning. It contrasts particularly well with tall Eleocharis (hairgrass) species and other plants with green color and finer texture.
Propagation poses no problems whatsoever. New shoots are continually produced and yet more quickly arise after trimming. Ludwigia x lacustris makes a good candidate for emersed culture, where it grows attractive flowers with yellow petals, in contrast to the inconspicuous, apetalous flowers of L. palustris. If any of the flowers should become pollinated, fertile seeds are unlikely to result, which is perhaps why this wonderful plant is not more widespread.
Sources used/further reading:
Peng, et al (2005). Systematics and Evolution of Ludwigia Section Dantia (Onagraceae). Annals of the Missouri Botanical Garden, 92, 307-359.
Photo #1 Submersed: US and International Copyright 2010 by Jeff U. All Rights Reserved
Photo #2 Submersed: US and International Copyright 2010 by Jeff U. All Rights Reserved