"Bunch" plants definitely not often seen enough, the genus Rotala offers some great beginner to expert aquascaping possibilities. They're fast growing true tropicals, some with brilliant wine-colored foliage under standard conditions.
These plants are better described as submersed water plants than totally aquatic. Like many genera used for aquariums, the Rotala are actually amphibious organisms that require a "dry" period, and have a quite different appearance when growing terrestrial.
Classification & Species of Use To Aquarists:
The classification of these plants goes all the way back to the origins of scientific naming; none other than Linnaeus himself described the genus. Rotala are part of the loosestrife family Lythraceae; a group containing the aquarium Diplidis as well.
These plants can be quite variable in structure and color depending upon growing circumstances. Notably, Rotala have definite emersed terrestrial and underwater/submersed forms; and do best when seasonally rotated between these two. Emersed stages have rounded, thicker leaves, that submersed become narrow, thin and lanceolate.
Rotala rotundifolia (HAMILTON) KOEHNE 1880
Synonyms:Ammania rotundifolia, A. latifolia, A. subspicata, Ameletia rotundifolia, A. subspicata, Borneo diplidis.
Natural Distribution & Ecology: The Far East; China, Formosa, Laos, Vietnam, Thailand, & India.
Physical Description:Pointed short (1/2-3/4" long by 1/8 inch wide) leaves underwater. Pale pink flowers on terminal heads of stems.
Rotala indica (WILLDENOW) KOEHNE
Natural Distribution & Ecology: Throughout tropical Asia. A "creeping" plant, easily spreading and popping up from under the substrate.
Physical Description:Leaves 1/8" to 1" in length. Flowers of deep pink produced on stem axillary heads.
Rotala macrandra KOEHNE 1880
Giant red rotala
Natural Distribution & Ecology:
Physical Description:Well named as "the giant red rotala"; R. macandra has beautiful large (3/4-1 1/4" long by 1/2 to 3/4" wide), thin red leaves that are unstalked, oppositely arranged and sharp at their points.
Rotala wallichii (HOOKER) KOEHNE 1880
Natural Distribution & Ecology: Southeast Asia. The most difficult of rotalas for aquarium culture.
Physical Description:Thin main stems with dense whorls of needle-thin leaves (1" long by 1/32" wide), 10-12 in number. Emersed leaves much more broad.
Rotalas grow better placed in small bunches together. Ideally these amphibious plants can be started and unmoved in a system that may be allowed to "go empty" of water, i.e. dry out, for the "low water season".
Substrate/Soil:Does best in rich, peat-loamy soils mixed in fine gravel or coarse sand. Iron based fertilizer and/or laterite is definitely beneficial.
Light/Lighting (intensity, spectrum, duration): Stronger lighting results in redder, wine-colored foliage. A good twelve hours a day of 10-20k lumens.
pH, KH, Other Chemical:Acidic to neutral waters for the entire genus (5.0-7.0); softer water (2-10 KH). Avoid ion-exchange soft-water that contributes free sodium, and obviously any addition of salt(s) to systems containing Rotala.
Temperature Range:Tropical ranges; upper sixties to low eighties F.
Species Kept With:Good with slow growing Cryptocoryne species and the fern Microsorium pteropus
Trimming:Can be done by pinching or cutting the rapaidly growing tips. If at all possible, do try allowing some emersed growth up and out of your water.
Rotalashould be grown out of water in the summer and underwater in winter. A warm, shaded area, ideally a lighted, covered aquarium will grant you the most production.
Sexual reproduction from flowers is a possibility; look closely for their numerous flowers at the axis of emersed leaves. These are composed within a bell-shaped calyx (like those of the Eucalyptus in miniature).
Best purchased locally (from a grower or friendly hobbyist); Rotalas do not take well to moving, especially to new water conditions. Better sent in emersed form and adapted to underwater use.
Rotalaspecies make great "bunch" plants; either for backgrounds or for highlighted central areas. Three of the listed species are at least as good as the plants in the genus Hygrophila, and deserve the attention they are finally getting.
Bear in mind that these plants may be used simply as submersed annuals, or if desired, "over-summered" as amphibious and re-submersed in the "winter" and kept perennially.
Baensch, Hans A. & Rudiger Riehl. 1993. Aquarium Atlas, v. 2. BAENSCH, Germany. 1212 pp.
Gasser, Robert A. 1978. Rotala Rotundifolia. FAMA 4/78.
James, Barry. 1986. A Fishkeeper's Guide To Aquarium Plants. Salamander Books, U.K.. 117 pp.
Riehl, Rudiger & Hans A. Baensch. 1987. Aquarium Atlas, v. 1. MERGUS, Germany. 992 pp.
Roe, Colin D. 1967. A Manual of Aquarium Plants. Shirley Aquatics, England. 111 pp.
Stodola, Jiri. 1967. Encyclopedia of Water Plants. T.F.H. Publications, NJ. 368 pp.
Commercial production of Rotala in Florida outdoor ponds. Stock is grown emersed for a time and then water level raised to casue it to transforms into submersed before cutting, bunching and shipping.
1 & 4) R. rotundifolia shown with shiny aerial leaves out of water and for sales in a retail setting.
2, 3) Two shots of the popular R. macracantha.