If you have ever spent time in an aquarium store, you have undoubtedly come across a Cryptocoryne or two. Indeed, these plants are most famous for their indispensable role in aquascaping freshwater aquaria. As organisms, however, crypts receive considerably less attention. Nonetheless, a handful of dedicated botanists have devoted time and effort to understanding this wonderful genus of tropical Aroids. What follows is a brief introduction to the world of Cryptocoryne plants.
Cryptocoryne is a genus that currently consists of around 60 - 65 species, all of which are native to tropical regions of Asia and New Guinea. Every few years it seems at least one or two new species are added to this list and without a doubt, more species await discovery. All crypts are considered aquatic to one degree or another. Ecologically speaking, however, species fall into four broad categories based on the types of habitats they prefer.
The most familiar crypts grow along the banks of slow-moving rivers and streams and find themselves submerged for a large portion of their life. Others grow in seasonally flooded habitats and experience a pronounced dry season. These species usually go dormant until flood waters return. Still others can be found growing in swampy forested habitats, often in acidic peat swamps. Finally, a few crypts have adapted to living in tidal zones in both fresh and brackish waters.
Like all aquatic plants, crypts face a lot of challenges living in water. One of the biggest challenges is reproduction. Despite their aquatic nature, crypts will not flower successfully underwater. If growing submerged, most crypt species reproduce vegetatively via a creeping rhizome. As such, crypts often form large, clonal colonies in both the wild and in aquaria, a fact that has made a few crypts aggressive invaders in places like Florida.
Given proper hydrologic cycles, however, crypts will flower and when they do, it is truly a sight to behold. As is typical of aroids, crypts produce an inflorescence comprised of a spadix with whirls of male and female flowers covered by a decorative sheath called a spathe. This spathe is the key to successful flowering among the various crypt species.
If the spathe were to open underwater, the inflorescence would quickly rot. Instead, most crypts seem to have an uncanny ability to sense water levels. At early stages of development, the spathe completely encloses the developing spadix in a water tight package. The tubular spathe continues to grow upward until the top has breached the surface. Consequently, the overall length of a crypt inflorescence is highly variable depending on the water level of its habitat. Crypts living in tidal zones take this a step further. Somehow they are able to time their flowering events to the ebb and flow of the tides, only producing flowers during periods of the month when tides are at their lowest.
With the tip of the inflorescence safely above water, the spathe will finally open revealing their surprisingly complex anatomy and coloration. It is a shame that most crypt growers never get to see such floral splendor in person. The spathe of many crypt species emit a faint but unpleasant odor. Additionally, some species adorn the spathe with fringes that, coupled with stark coloration, is thought to improve the chances of pollinator visitation.
Pollinators are poorly studied among crypts, however, it is thought that small flies take up the bulk of the work. Lured in by the promise of a rotting meal on which they can feed and lay their eggs, the flies become trapped inside the long tube of the spathe. Like the pitfall traps of a pitcher plant, the inner walls of the spathe are coated in a waxy substance that keeps the insects from crawling out before they do their job.
In general, the female flowers mature first. If the insect inside has visited a crypt of the same species the day before, it is likely carrying pollen and thus deposits said pollen onto the stigmas of the current crypt. After the female flowers have had a chance at being fertilized, the male flowers then mature. The insects inside are then dusted with new pollen, the walls of the spathe lose their slippery properties, and the insects are released in hopes of repeated the process again.
To the best of my knowledge, most crypts are not self-compatible. Instead, plants must receive pollen from unrelated individuals to set seed. Because large crypt colonies are often made up of clones of a single mother plant, sexual reproduction can be rather infrequent among the various species. Nonetheless sexual reproduction does occur and the seeds are produced in a different way than most other aroids. Instead of berries, crypts produce their seeds in a aggregated collection of fruits called a syncarp. When ripe, the syncarp opens like a little star and the seeds float away on the current.
One species, Cryptocoryne ciliata, takes seed production to a whole different level by producing viviparous seeds. Before the syncarp even opens, the seeds actually germinate on the mother plant. In this way, tiny seedlings complete with roots and leaves are released instead of seeds. Seedlings have a much greater surface area than seeds and readily get stuck in mud as well as other aquatic vegetation. In this way, C. ciliata offspring get a jump start on the establishment process. It is no wonder then that C. ciliata has one of the widest distributions of any of the crypt species.
Despite plenty of overlap among the ranges of various crypt species, the genus displays an amazing array of variation. Some have likened crypts to Araceae's version of Darwin's finches in that the unique ecology of each species appears to have created barriers to species introgression. Though hybrids do occur, each crypt seems to maintain its own niche via a unique habitat requirement, differing flower phenology, or a specific set of pollinators. It would appear that much can be learned about the mechanics of speciation by studying the various Cryptocoryne and their habits.
Unfortunately, the limited geographic distribution and specific habitat requirements of crypt species is cause for concern. Many are growing more and more rare as human settlements expand and destroy valuable crypt habitat. As popular as some crypts may be in cultivation, many others have proven too idiosyncratic to grow on a commercial level. More work is certainly needed to properly assess populations and bring plants into cultivation as a form of ex situ conservation.
Proper study is further complicated by the fact that many crypt species are highly plastic. They have to be in order to survive the rigors of their aquatic environment. True species identification can really only be assessed when flowers are present and some populations seem to prefer vegetative over sexual reproduction a majority of the time. A multitude of subspecies exist, though the degree to which they should be formally recognized is up for debate.
I think it is safe to say that Cryptocoryne is a genus worth far more attention than it currently receives. They are without a doubt important components of the ecology of their native habitats and humans would do well to understand them a bit better. With a bit more attention from botanical gardens and other conservation organizations, perhaps the future for many crypts does not have to be so bleak.