Hydrocharitaceae is a plant family that includes some of the most economically significant plants in the world, both positively and negatively. Many municipalities, for example, have spent millions of dollars attempting to eliminate Hydrilla verticillata from fishing lakes and public water sources, yet the tropical fish business would very likely cease to exist as we know it without Vallisneria spiralis and Egeria densa. The fascinating thing about these plants is that they come in such a broad diversity of shapes that even expert aquarists may not realize they belong to the same family.
The Hydrocharitaceae family includes 15 genera, all of which are aquatic. They range in size and shape from thin-stemmed, highly branching purely aquatic plants with short, narrow leaves (Hydrilla) to strong, emergent plants with rosettes of stiff, serrated leaves and huge yellow blooms (Hydrilla) (Stratioides). When reading a description of the family, one notices that the forms vary so greatly that it begs the question of how and why these plants are connected.
The fundamental architecture of the various plant components, however, changed, is what connects them, as with all groupings of related species. When we examine the different components of the plants closely, we see that they are all quite similar.
Those features are detailed in the official description of a specific species to the degree that they aid in distinguishing between species within a genus, a genus within a family, and so on. A similar description follows. It defines the family and highlights all of the main family structures.
Hydrocharitaceae:
Cosmopolitan: 15 genera. Three genera (Enhalus, Thalassia, and Halophila) are marine and so not included in this analysis.
“Annual or perennial, dioecious or monoecious, annual or perennial.” Varieties of leaves, normally submerged, seldom floating, or partially emergent. Flower placed in a bifid spathaceous bract or between two opposing bracts, bisexual or unisexual; males frequently more than one, females solitary when unisexual. Perianth segments are free, 1- or 2-seriate, with 3 or rarely 2 in each series; inner series are frequently showy and petal-like when present. Stamens 1 to many, in 1 or more whorls, the inner ones staminodial at times. Placentas parietal, sometimes projecting almost to center of the ovary; fruit globose to linear, dry or pulpy, indehiscent or rupturing irregularly, seeds many, smooth, warty or spiny.”
Quoted C.D. K. Cook’s Water Plants of the World
So, what does it all mean? The following is a clause-by-clause breakdown of the preceding description.
- 15 genera: cosmopolitan: There are 15 genera within the family. They occur all over the habitable planet.
- All aquatic, 3 genera (Enhalus, Thalassia, and Halophila) are marine, and thus excluded from this account: All members of the family are strictly aquatic. The 3 genera mentioned live in the ocean and so are not included in the book from which this reference was taken.
- Annual or perennial: Plants may be short-lived or persistent over time. Annuals depend upon seed production for year-to-year survival, whereas perennials might die back every year but retain a long-lived rootstock.
- dioecious or monoecious: Literally, “two houses”, and “one house”, respectively, from the Greek root oecium, “house”. Dioecious plants are those that produce male and female flowers on separate plants. Monoecious plants are those that produce flowers of both genders on one plant.
- Herbs: Herbaceous plants are those that produce soft, non-woody tissue only.
- Leaves vary: Leaves exhibit a variety of forms.
- usually submerged, rarely floating or partly emergent: most species within the family are strictly aquatic, meaning that no part of them with the possible exception of flowers rises above the water line. Few produce floating leaves under very specific conditions, and some of them even rise above the water or can survive when the water line drops.
- Flower arranged in a bifid spathaceous bract or between 2 opposite bracts: Bifid means split into two parts. Spathaceous means having a sheathing lateral organ or pair of organs that usually open on one side and that enclose an inflorescence (an aggregation of flowers). A bract is a reduced or modified leaf, particularly the scale-like leaves in a flower cluster. So a ‘bifid spathaceous bract’ is a sheathing, made of modified leaves, and split into two parts, surrounding a flower cluster.
- bisexual or unisexual: Flowers may exhibit characteristics of both genders, staminate (male) or pistilate (female).
- when unisexual then males usually have more than 1, females solitary: In those cases where a flower is unisexual and male, there may be as few as 1 flower present, but usually not. When the flower is female, there is always only 1 flower present.
- Perianth segments free: A perianth is a nonessential appendage of a flower, situated outside of the whorl of stamens in the center of the flower. The perianth includes both sepals (part of the Calyx, or outermost whorl of the floral envelopes) and petals or other segments homologous with them. When the segments of the perianth are said to be ‘free’, it means that they are not fused to one another.
- **1 or 2- seriate: arranged in 1 or 2 rows or series.
- **3 or rarely 2 in each series:
- inner series when present is usually showy and petal-like: In those plants that have an inner series of perianth segments, those segments are colorful and large.
- Stamens 1 to numerous, in 1 or more whorls, the inner ones sometimes staminodial: In staminate flowers, the number of the stamens from 1 to several. They are arranged in whorls, numbering at least 1, and the inner whorl occasionally comprises what is called, ‘staminodia’. Staminodia is sterile organs, resembling stamens, and presumably of staminal origin.
- Ovary inferior: The ovary, or seed-producing organ, is underneath all of the other flower parts.
- **of 2 to 15 united carpels: The female flower is made up of several parts, the ovary, the stigma, and the style. These combine to form the Pistil. A carpel is one of the foliar units of which a pistil is composed. When these are fused together, they are said to be united.
- placentas parietal: The placentas are the structures upon which the ovules are arranged within the ovary. When they are parietal, they rest on or arise from, the ovary wall.
- occasionally protruding nearly to the center of the ovary: In this case, they extend so far from the wall of the ovary that they nearly meet in the middle of the ovary.
- fruit globose to linear: Fruits are seed pods and to be globose is to be rounded., or nearly spherical. To be linear is to be elongated so that the side of the fruit are nearly parallel.
- **dry or pulpy: Seeds are
- indehiscent or rupturing irregularly: In reference to fruits, indehiscent ones are those that remain closed and do not shed their seeds readily, i.e., Ficus spp. (Figs). Ones that rupture irregularly or those that explode, scattering their seeds far and wide, i.e., Wisteria chinensis are said to rupture.
- seeds numerous, smooth, warty, or spiny: Each flower produces numerous seeds, which vary in form as the list implies.
Determining which features define whether a plant belongs to this family is still a difficult task. The most likely method is to compare the descriptions of each of the genera in the family to each other and, most significantly, to the overall description of the family itself. I’ll go through the genera alphabetically and analyze each description as described above.
Leaf: form, Root form, Flower desc. other characteristics.
Description:
Blyxa:
Monoecious or dioecious submerged annuals or perennials. Corm-like or up to 60cm long stem. Leaves are linear, spirally arranged, radical, or along the stem; the base sheathes the stem; the margins are whole or minutely serrate; the apex is attenuate; the nerves are parallel, and the midrib is noticeable. Sessile or stalked spathes, tubular with 6 longitudinal ribs, bifid at the tip. 1 flowered or up to 10 blooms in male spathes of dioecious plants. Flowers may be unisexual or bisexual, with female and bisexual flowers being sessile and male flowers stalked. Sepals are three, linear or linear-lanceolate, green, and persistent. Petals are three, linear, longer than the sepals, white, flaccid, fringed, diminished, or nonexistent. Stamens three, six, or nine; filaments capillary; anthers linear or lanceolate 2-locular. Fruit straight or linear-lanceolate, membranous; seeds 10 to many, elliptic or fusiform, 1 to 2 mm long, smooth or spiny.
Translation:
Submerged:
Living fully submerged
Whether monoecious or dioecious:
As previously stated, dioecious plants develop male and female blooms on different plants. Monoecious plants have blooms of both sexes on the same plant.
Annuals against perennials:
Plants may be either short-lived or long-lived. Annuals rely on seed generation to survive year after year, but perennials may die back every year yet preserve a long-lived rootstock.
Corm-like or up to 60cm long stem: A corm is a solid, swelling portion of a stem that is normally underground, such as the “bulb” of Crocus and Gladiolus. This most likely indicates that in certain settings, such as shallow water, the stem thickens and hardens, but in others, such as deeper water or situations with heaps of soft silt on the bottom, the stem is softer and more brittle.
Linear, spirally organized, radical, or along the stem leaves:
This plant’s leaves are long and thin, grouped spirally on the stalk (if you were to look at a cross-section of the stem, or if you were to remove the leaves, you would see that the leaf bases are arranged spirally). Radical leaves are those that sprout from the base or the crown of the plant. In this situation, the leaves will either be connected to the corm or spread out along the stem, depending on the circumstances under which the plant is developing.
stem base sheathing:
The leaf bases wrap around the stem for a short distance before leaving it.
whole or minutely serrate margins:
The leaf margins are smooth or very finely serrated.
attenuate the apex:
The leaf’s tip progressively tapers.
Parallel nerves, prominent midrib:
The veins of the leaves run parallel to one another. The main vein protrudes from the leaf’s surface.
Sessile or stalked spathes:
From the above, we know what spathes are. Sessile refers to the absence of a stem or stalk. The organ in question, such as a flower, leaf, or spathe, grows straight from the stem. Stalked indicates that there is an uncertain length stem.
tubular, with 6 longitudinal ribs and a bifid apex:
In this scenario, the spathe is shaped like a tube, with 6 ribs running the length of it. In the end, it is divided in two.
1 flowered or up to 10 flowers in male spathes of dioecious plants:
Most plants have just one blossom per spathe. There may be up to ten blooms present in situations when the spathe includes male flowers.
Female and bisexual flowers are sessile, whereas male flowers are stalked:
Flowers may be either male or female, or both. Without a stalk, all female blooms and blossoms of both genders are retained close to the stem. All solely male blooms are stalked.
3 Sepals:
Sepals are the flower’s outermost petals. Before the bloom develops, the sepals cover it. There are three of them per bloom in all Blyxa species.
linear-lanceolate or linear-lanceolate:
Linear refers to being straight and thin. Lanceolate refers to being broader in the center than at either end and having a pointed tip. In the case of Blyxa, they might range from linear to narrowly lanceolate.
green, long-lasting:
The spathes are green in color and do not fall off as the seeds grow.
Petals three, linear, longer than the sepals, white, flaccid, fringed, diminished, or absent:
Obviously, each flower has three petals. The petals are white and long and slender, reaching beyond the sepals. They have a fringed border and droop. The petals, on the other hand, may be reduced to insignificance.
Stamens 3, 6, or 9; capillary filaments:
There are 3, 6, or 9 stamens per flower depending on the species, and the stalks on which they stand are exceedingly thin, or hair-like.
2-locular anthers:
linear or lanceolate The anters are separated into two compartments, or cells, and are long and narrow to considerably expand in the center.
Ovary with three carpels and a long, capillary beak:
The ovary has three compartments. The ovary is long and narrow, with a long, hairlike protrusion from one end.
styles 3, entire, linear, united at the base:
The stigma or stigmas are carried by the styles, which are short or long, simple or branching stalks that emerge from the ovary. It is the pistil component that connects the ovary to the stigma. There are no notches, indentations, serrations, or anything else that might ruin the style’s surface. In this scenario, there are three styles per flower, one per carpel, they are thin, and they are fused at the base, rather than originating from locations so far apart that they would be impossible to separate.
Membranous fruit, linear or linear-lanceolate:
The fruit, which is just a fertilized ovary, is long and thin like the ovaries. The ovary thickens in the center due to the development of the seeds, thus the linear-lanceolate shape. In this example, membranous means that it is thin, soft, and malleable.
10–20 seeds, elliptic or fusiform, 1–2 mm long, smooth or spiny:
Each fruit contains at least ten seeds and typically many more. The seeds are oblong in shape, with widely rounded ends and sides. They might have a smooth feel or be covered with tiny spines.
Other considerations:
Blyxa:
About ten species of submerged, stoloniferous aquatic plants belong to the ancient world’s tropics. Lvs is tall and linear, with pronounced midribs…
B. echinosperma Monoecious, lvs basal, sheathing, to 1 ft. or sometimes longer, dark green, flrs bisexual, white, 1 or rarely 2 in a spath, stamens 3. Fr. Linear, to 2 ¾” long. Phillipine I and S. and E. Asia, Ss to E India and trop Australia.