Nature abhors a vacuum, including muddy shores freshly exposed by the seasonal retreat of erstwhile shallow ponds. Exposed barrens spell opportunity for ambitious pioneer species. Colonization happens fast. To meet plants you otherwise seldom encounter, don your boots and don’t sink in chin-deep.
There are no pre-existing competitors on new mud. All newcomers can stake a claim. Nobody is competitively excluded, so diversity abounds. Let’s see, in the postage stamp mudhole I explored today I recall seeing (running out of fingers and toes) over 20 plant species.
Who’s first to settle? Floating plants carpet the receding water and are the first settlers, although the species composition shifts substantially. The pudding-dwellers arrive for the most part floating as whole plants, or as little breakaway pups, or as fragments, or as seeds or spores. The mud community is far more diverse than the species readily spotted afloat.
Green lowlifes on smelly mud take me back 470 million years to when plants originally strode forth from water to land. Standing on the mud today was a window into pre-pre-history. Look who we find, at least two examples of the most primitive still-existing plants, liverworts, straight out of a museum diorama. I’ll bet today’s liverworts are almost unchanged from the first terrestrial plants, not counting bacteria and algae.
The real fun is seeing who the castaways are and their adaptations to the mud world. What are the facts of life on quicksand? It is sopping wet, unless the sun bakes the surface dry. The habitat is too suffocatingly soggy to invite extensive roots. It smells like sulfur. Nutrient acquisition must be a challenge.
At least one resident brings its own nutritional assistance. The floating fern Azolla has folded into its leaves symbiotic nitrogen fixing Cyanobacteria, microbial fertilizer factories. It can have all the nitrogen it wants. The other floater in the photo below, Salvinia, has every third leaf modified into a big nutrient mop no doubt able to help with the fertilizer problem in its own fashion.
The next rain spells doomsday for these precarious species, although each is ready for rainageddon in its own way. They arrived floating, and can depart the same way, no problem? What about those who came by seed and need to make new seeds? They work fast. The Pentodon in the photo below can bloom and fruit while still mere baby seedlings, not a moment to waste. After that safe start, the longer they live the bigger and more fecund they can be.
The Ceratopteris ferns, water sprites, can float and make bulbils to disperse as clones, and even better, they mature from spores to reproducing adults in as little as three months to complete their sexual cycle.
Returning to seeds, one way to win a race is speed, as we just discussed, but there’s another way… a head start like the Nebraska Sooners. Barnyard Grass, Echinochloa crus-galli, jumps the gun by having the rare ability for its seeds to germinate in the absence of oxygen still submerged or buried in stinking mud. That is why this grass is a pest in rice paddies.
Another response to re-rising water is to live with it. The Southern Marsh Yellow Cress, Rorippa teres, sprouts all over the mud. Not only does it flower and set seeds early in life, it can probably also live submerged if its relatives are a good measure. Although I do not have data on this species per se, some of its close kin have survived and grown during underwater tests as long as three months. Let it rain!