FAQ - Plants - Alismaceae
The family Alismaceae (Al-is-MAH-kay-ee) is a highly diverse group of plants whose members can be found in streams, ponds, and flooded areas throughout the habitable world. Their importance to their local ecologies and the usefulness of some species to hobbyists make them plants of interest to many people. From the diminutive Sagittaria filiformis, with its thin, short leaves and tiny white flowers, through the type genus Alisma, with its fleshy green leaves and sprays of small white or pink flowers, to the largest of the Sagittaria and Echinodorus species, there is a large enough range of leaf form and growth habits to keep taxonomists busy and hobbyists intrigued well into the future. In fact, the name of the entire family is evidently in question. Most sources list it as Alismataceae, while a few list it as Alismaceae. It does make one wonder where that extra –ta- comes from. Be that as it may, there are 11 genera in the family, at least four of which occur naturally in the United States. They are Alisma, Damasonium, Echinodorus, and Sagittaria. The other genera are Caldesia, Wisneria, Burnatia, Luronium, Limnophyton, Ranalisma, and Baldellia. Most of these are represented by a single, or at most three or four species, and are from Africa and Europe. The broad distribution of the plants in the group indicates that the family has existed for a very long time, probably being present on Pangea, the supercontinent of so long ago.
It might be fairly asked, “If these plants are so diverse in form and habit, what then makes them so much alike that they can be included in the same family?” The answer is that while the leaves may be highly diverse, the basic structures of the plants are similar, and patterns can be found in comparisons of how the plants grow and reproduce.
The first similarity is in the root. All of these plants grow on a rhizome that may exhibit some degree of woodiness from soft, herbaceous stems to tough, fibrous masses of semi-woody tissue. The rhizomes exhibit varying degrees of branching, with some producing offspring every few weeks, meaning that the plantlets are close together on the horizontally growing rhizome, producing a clump of plants that fan out from the starting point (Sagittaria lancifolia), while others produce a plantlet only once every several months (Echinodorus spp.), producing less dense clumps. Most of the rhizomes grow horizontally, but some grow vertically, with offspring growing in clusters around the parent plant (Sagittaria montevidensis). Others produce runners, with new plants being produced every few to several inches. These plants eventually form thickets on sandy or muddy substrates in shallow or deep water.
The leaves emerge from the rhizome in a rosette pattern, and may be on petioles (stems) of varying lengths from very short to two feet or more. The petioles are sheathed at their bases, which may be observed as the little wing-like structures that emerge from the inside of the base of the leaf stem, running up the stem a couple of inches. Immature leaves are always filiform (hairlike), subulate (bladelike), or ovate, and reach their mature form only after two to several leaves have been produced. Leaves are usually conspicuously veined, with the veins sometimes being quite pronounced. In those species that grow either submersed or emersed, there are almost invariably leaf forms for each situation. Submergent foliage is usually much softer and less dense than emersed foliage, which can often be pretty rugged. Those species that produce different leaf forms according to prevailing conditions do so rapidly. When the floods come, emergent Echinodorus plants immediately shift to submersed leaf forms, and when the water goes away in the dry season, they respond by producing the tougher emergent foliage and flowers.
Flowers, the true indicators of differentiation, are always borne on a usually branched but sometimes unbranched stem, and are arranged in whorls of 3 to 12 or 15 at intervals up the stem, which culminates in a cluster of flowers at the apex. Each flower has three petals, whose size may range from a few millimeters (“scale-like” is the term used to describe some of them) to more than an inch wide. Flowers are usually white, with a few species producing pink or purple flowers. Flowers frequently have yellow centers, and one species, S. montevidensis, has a large red spot at the base of each petal. Plants may be monoecious, with flowers of both genders on one plant, or dioecious, with each gender being on separate plants. When they are monoecious, the female flowers are always carried below the male flowers, allowing wind-blown pollen to fall onto the female flowers in the absence of bees. Flowers may be unisexual (Sagittaria) or bisexual (Echinodorus, Alisma).
Modes of reproduction include the production of runners (Sagittaria subulata, Echinodorus tenellus), rootstock division (Alisma, etc.), seed production, and the production of adventitious daughter plants at the nodes of the inflorescence. The rate of seed production exhibited by most of these plants indicates that they are very important food sources for many species of animals. As a group, the Alismaceae probably cannot depend too heavily on one system of reproduction. Seeds might be eaten or washed away; runners are effective, but thickets of plants are subject to grazing. Rootstock division is nice, but that fleshy rhizome has got to be tasty to somebody, especially sitting in the mud, fat and fleshy in the dead of winter. Many species of Sagittaria produce winter storage bulbs that have long been eaten by people and animals. One of their common names is “Duck Potato.”
Seeds are of a form called an acene, or achene, which is a dry, indehiscent seed capsule with only one seed enclosed. The seeds are arranged radially, edge on, around a central core. The resulting cluster of seeds may be flattened or nearly spherical, with seeds numbering from a few dozen to several hundred. The surface of the cluster is rarely smooth, with the texture being either only mildly textured to being almost spikey, giving one genus, Echinodorus, the common name “Burhead.” As the seeds ripen, they fall away from the old flower and either float away to new grounds on water, or land in the mud and hope to get pushed into the mud before they are eaten. They germinate almost immediately in many cases, giving them time to get established before winter dormancy or inundation. By the same token, we have had seeds of S. montevidensis and various spp of Echinodorus and Alisma germinate after months or years of dormancy.
Many of these species live in areas that are not always under water, and may even dry up completely, so their seeds need to be able to survive long periods of drought.
What follows is a discussion of each of the genera, with particular attention being paid to the two important genera, Sagittaria and Echinodorus.
The type genus, Alisma, is represented by at least three species and a couple of sub- species, depending upon the source that you choose. A. plantago-aquatica, or the so-called “Water Plantain,” is the most common. A. triviale and A. subcordatum are treated as subspecies of A. plantago-aquatica by some taxonomists and as separate species by others. A. lanceolatum, or the “Narrow Leaf Water Plantain,” occurs in Europe and has only recently been introduced to the American market. It is probably destined to become a weed in many parts of this continent. Endemic North American species can be found nearly everywhere except in the extreme north and at the highest elevations. The leaves in all Alisma species arise from a central rootstock, producing a rosette of lanceolate to ovate leaves on stems that are frequently two or three times the length of the leaf blade. Leaves may grow to large size if conditions are suitable. Large for A. plantago-aquatica would be 4” long and 2.5” wide. Flowers are always produced on long, branched stems that rise well above the leaves. The flowers are white (A. plantago-aquatica) or pink (A. lanceolatum), as is typical of the family. Seeds are small, flat, disk-like acenes and are arranged, side by side, in a circle around the center of the flower. Most Alisma species live in shallow water along pond margins that may dry up or not. One species, A. geyeri, lives in deeper water. Because of their seed production, all Alisma species can become rather invasive, so they must be thinned periodically and/or prevented from producing seed.
The genus Wisneria comprises three species, all of which are endemic to tropical Africa and Madagascar. These plants are always submerged or may have partly floating linear to oblanceolate leaves that can grow to one meter in length. It is sometimes difficult to distinguish between the leaf blade and its stem, owing to the narrowness of the leaf. Rising just a few inches out of the water, the small flowers are held very close to the stem. As is found elsewhere in the family, male flowers are higher on the inflorescence than the females are. The lower whorls sometimes produce young plants. The three species are W. filifolia from Madagascar, W. triandra from tropical Africa, and W. schweinfurthii, also from tropical Africa. This group of plants seems as if they would be good in the aquarium, but are not now available in the hobby, as far as I know.
The next genus is Caldesia. There are four species in Caldesia, and they are found over a huge geographical range that extends from Europe, through India and over to China, down through tropical Africa and on to Australia. It should come as no surprise that some of them are endangered these days because of habitat destruction. The four species are C. parnassifolium from Europe; C. reniformis from tropical Africa, India, and Australia; C. oligococca from India, Ceylon, and Australia; and C. grandis from India and China. These plants are either submerged or produce floating leaves, and rarely come out of the water except to bloom. The leaves are broadly elliptic to broadly ovate, with either pointed or rounded apices. The leaf bases are truncated or chordate.
The genus Luronium contains just one species, L. natans. It is a low-growing, creeping plant with small, ovate leaves and 1” diameter white flowers. Flowers are produced in groups of 1 to 5, emerging from the same nodes as the leaves. These same nodes produce roots. Seed heads are roughly hemispherical and contain many seeds. This genus is native to Europe and has expanded its range into Britain.
Ranalisma, the next genus, comprises two species, R. humile and R. rostratum. These are easily confused with Echinodorus and have been given that name by several authors over the years. R. humile is a weed in rice paddies in West Africa. R. rostratum grows in the Malay Peninsula and Indochina. They are low-growing herbs with erect or spreading, linear to ovate leaves. Flowers are borne on a short stem singly or in groups as large as three. Flowers are white, small, and bisexual. Ranalisma species grow in shallow water and in areas that dry out seasonally.
Limnophyton comprises three species, L. obtusifolium from tropical Africa, Madagascar, India, Ceylon, and the Malay Peninsula; L. angolense from tropical Africa (Angola); and L. fluitans, also from tropical West Africa. All of these plants occur in still or slowly flowing water in swamps, irrigation ditches, and ponds. They produce erect leaves on long petioles. Leaves have a rounded or blunted apex and wedge-shaped or sagittate bases. Flowers are held above the leaves on a stem that sometimes branches two or three times near its base and produces 4 to 7 whorls of flowers after that. The small white flowers are arranged with the male flowers near the top and female, as well as bisexual, flowers near the bottom.
The genus Baldellia is represented by only one bona fide species, B. ranunculoides. Another species, B. alpestris, is sometimes recognized; it hails from Europe and North Africa. The common name for Baldellia is “Siberian Bog Pink,” and it is sold under this name. Baldellia resembles Echinodorus and is sometimes included with it. The leaves are narrowly lanceolate and are held on thin stems, sometimes of considerable length. Leaves rarely exceed 2” in length, but the petiole can be 6 or more inches long when the plants are crowded. Flowers are held singly on small stems that radiate from the end of a larger stem. Flowers are pink in the morning and fade nearly to white by late afternoon. Seeds are small (2mm) and are typical of the family, that is, beaked, ribbed, and ovoid. This plant grows in shallow water along streams and pools, forming colonies because of its habit of producing runners.
Burnatia, with only one species, B. enneandra, grows in slow streams, pools, and swamps in tropical Africa. It produces narrowly lanceolate to ovate leaves on long, erect stems. These plants can grow to large size, with petioles up to 16” long and leaves up to 6” in length, and will grow either submersed or above water. It being a dioecious species, the flowers are held on different plants. Male flowers are very small (1 mm petals), but are actually larger than the female flowers, where the petals are nearly nonexistent. This would probably make a good aquarium plant too, but alas, it is unavailable to us.
The genus Echinodorus is certainly one of the largest genera within the family, with about 50 species. It comprises one of the finest collections of aquarium and bog plants of any genus. Both aquarists and outdoor water gardeners will find members of this genus that will stand out in their plant displays. Some species work well for both.
The smallest Echinodorus is the diminutive E. tenellus, which works well in aquarium foregrounds. E. tenellus and E. quadricostatus grow very much like Sagittaria subulata, in that they produce runners. They grow to no more than about 6” tall, and have narrowly lanceolate leaves on long petioles. One might also keep the so-called “Amazon Sword Plant,” E. amazonicus, or E. bleheri, both of which make stunning centerpiece plants for aquaria, with their large, handsome, broadly lanceolate leaves on short petioles. These produce inflorescences just as the rest of the species, but here, the flowers are reduced and the plant readily produces adventitious offspring, as we see in so many other species. These are species that occur in lowland tropical climes, as opposed to higher latitudes or elevations, and so do not do well in cooler situations.
Pond and bog plant growers can select from a number of robust, floriferous species that fit well into large or small pond or bog situations. Some of the same ones that work in aquaria also work in ponds, frequently growing (in the absence of goldfish or koi) into eye-catching specimen plants in one to two feet of water. These include E. osiris (“Melon Sword”), E. rosaefolia, E. horemannii (“Jade Sword”), E. ‘Red Rubin’, and E. uruguayensis. Many of them are cold tolerant and will grow for years without special care. In the spring E. uruguayensis produces bright red, lanceolate leaves that float on the water. Flowers soon follow and when several of them are in full bloom it is most attractive. The springtime blush of youth soon wears off, though, as the plants begin to produce their brown seeds and young plantlets. E. “Red Rubin”, E. rosaefolia, and E. osiris become quite beautiful in a pond, with their large, dark red leaves.
Within the genus, leaves may be lanceolate, ovate, or chordate, bright green or dark red, or variegated with red or cream. One species, E. berteroi, which happens to be native to this area, produces translucent green submersed leaves. For this reason, it is sometimes referred to as the “Cellophane Sword”. Many species produce several types of leaves according to their stage of development or the prevailing environmental conditions.
Flowers are typically held above the water on long, branched stalks that produce numerous three-petaled, white or rarely purple flowers that are grouped in clusters at intervals along the flowering stem. Petals may be as small as a few millimeters in width to as large as one inch. Flowers are always bisexual. Seeds are numerous and are arranged around a central core, forming a small ball of seeds at the end of a short stem. Their collected ends sticking out from the center form a prickly surface that gives the group its common name, “Burhead”. Adventitious daughter plants also form in the axils between the individual flower stems and the main stem. This occurs in high humidity or when the stem touches the water. These plants can be removed from the parent plant when they have roots or root buds and are easy to break free. Most Echinodorus species are very easy to grow.
Damasonium, one of the four genera to be found in North America, is represented here by only one species, D. californicum, although there are five other species within the genus. D. californicum is found only in the northern part of the state, is difficult to find, and probably hard to grow in southern California. The rest are from Europe, N. Africa, the Orient, Iran, and S. Australia. They have definitely gotten around. Damasonium alisma (“Starflower”), which can be found scattered from Great Britain through Europe and down to North Africa, grows in shallow water, producing floating lanceolate leaves and small white flowers held slightly above the water. D. minus (“Starfruit”) is a weed in rice fields in Canada. D. bourgaei, from Europe, grows in areas that dry out periodically. It produces small chordate leaves and small white or pink blossoms.
The last genus, Sagittaria, is the largest and most diverse. As mentioned above, this genus is represented by species as diverse in form as the grass-like S. filiformis and the gigantic S. montevidensis. As in Echinodorus, there are plants in this genus that are suitable for the aquarium, the pond, or both.
In the aquarium, S. subulata and its dwarf counterpart, S. subulata subulata, are the most popular, with S. filiformis being too hard to find in the commercial market to be much used by anybody for anything. They all produce thickets of varying heights, according to type. Reproduction is most often accomplished by the use of runners, although seeds are produced and do germinate. In the aquarium, they are used as a lawn in the front of the aquarium or as a screen across the back. In the pond, they make an interesting white-flowered lawn in shallow water, or as under-plantings for water lilies. They are good as oxygenators.
In the bog, the sky is the limit. S. montevidensis, with its large sagittate leaves and red-spotted flowers, makes a great accent plant on a pond margin or a specimen plant in a barrel planting. S. lancifolia, or “Bulltongue” can go in with taller plants in the background of the scene. It is robust enough to compete with Cyperus papyrus, tall Irises, and other large and aggressive plants. Its flowers are large and typical for the genus. There are at least three forms of this plant: a green-stemmed variety, a red-stemmed variety, and one with red variegations on the base of the stem. Its leaves are very narrow, while those of the green and red varieties are broad. S. graminea is useful in low bogs in the front of the pond or on the sides. It colonizes a large area with its runners, as do many other emergent species, including S. sagittifolia and S. latifolia.
One interesting point that is worth mentioning here is that as Sagittaria develop from seeds, they exhibit all of the leaf forms of the genus up to their own mature form, as they advance to their mature form. In other words, all of them start out with filiform leaves. The first group, the three subulate ones, never grow beyond the subulate form, which is next after filiform. The largest of the subulate group, S. subulata, sometimes produces small, spotted, ovate leaves at or slightly above the water surface. The next group stops at ovate or lanceolate leaves. Species in this group include S. lancifolia, S. graminea and all of its forms, and others. The last group, the sagittate (arrowhead-shaped) leaved species, go through all of the earlier leaf types and finish off with sagittate leaves of various sizes and shapes. There are thin ones, broad ones, long ones and short ones, small ones and large ones, but they are all sagittate. Species in this group include S. sagittifolia, S. montevidensis, S. latifolia, and many others.
Methods of reproduction among Sagittaria include the production of runners, which put the offspring at some distance from the parent plant (S. subulata, S. graminea, S. latifolia). These plants typically produce underground storage tubers for their dormancy. These are used by many animals and native peoples as a food source. A Sagittaria might also merely divide at the rootstock (S. lancifolia, S. montevidensis). In the case of S. lancifolia, the root is a rhizome that branches at odd intervals as it grows horizontally across the substrate. In S. montevidensis, the root grows vertically, with the offspring growing clustered around the parent. The parent almost always dies in the winter, leaving a circle of daughter plants to use the spot in the spring. Lastly, there is seed production, which in some species can mean a lot. One well-cared-for S. montevidensis specimen might easily produce several thousand seeds over the course of a season. All three methods of reproduction are represented in all of the leaf form categories.
For use as a potted plant, the species that produce runners are less suitable than the “clumpers” because they tend to crowd their pots. These species are better suited to use in more open settings, such as a naturalized bog planting.
All Sagittaria species are able to grow in San Diego. Many of them come from very cold winter areas, so nothing that southern California has to offer is any threat to them. Some species, S. montevidensis in particular, are not always winter tolerant, so you should be sure to collect seeds each summer and fall to germinate in the spring. Maintenance varies with the type of plant. Subulate species need to be thinned from time to time or they can crowd out other plants, as well as each other. All of the emergent species must be kept clean of dead leaves, as with any other plant. Those that produce runners need to be thinned if they are in a restrictive area. It is never a bad idea to repot specimens each spring.
Without doubt, Alismataceae is an important family of plants with two particularly important genera, Echinodorus and Sagittaria, within it. These plants are useful not only as efficient oxygenators, but also as decorative additions to our aquatic gardens, both under water and above it. I can usually find space for at least two or three species in my pond and aquarium plantings.