Which Came First, the Chicken or the Egg, the Moss or the Vine (Both?)

There’s something intriguing about the miniature self-contained ecosystems on swampy shady palm trunks. Lots of pushing and shoving, you know, lichen challenging moss kinda thing.   Who stands their ground, and who gets displaced?   But it’s not all pushin’ and shovin’.   Today’s nice friendly relationship is —so subtle you might question its reality, but I believe. 

Deep in the frog kingdom lives a moss called Syrrhopodon incompletus, which is hard to say but simple to spot as the dark green mats enjoying shaded palm trunks where the dark water is up over your ankles (unless you are on a nice boardwalk in Riverbend Park).   Brush off that spider, and look upward to the vines climbing the trunks.  Largely Virginia Creeper.

VA Creeper

With some luck in the right place you’ll see that the climbing vine and moss tend to hang out together, frequently with the moss flanking the vine as it rises into the tree.   

Moss and vine together

How that might come about is easy to imagine:  the moss makes a nice water-retentive substrate for the vine’s thirsty roots high above the moist nutritive ground.

Or:

Maybe the vine is a conduit for water and nutrients washing down the trunk.  You know, like those rain chains you can use in place of a downspout.    Maybe the vine is a “river” and the moss the “fertile floodplain” along the river.

Togetherness

Let’s go to the evidence.   Start with the vine using the moss.  It makes obvious sense.  Vine roots need water and nutrients, and moss is a storehouse. Secondly, studies on other plants in other places have shown epiphyte mats (such as moss) to feed plants with roots penetrating the mats (such as Virginia Creeper).   That is, our narrow case fits a broader known pattern. Third, and this is iffy at best, the Virginia Creeper’s clinging root pads grab the moss so tightly that when you pull the vine from the tree, it takes moss with it.  (A skeptic might say, that shows clinging but not proving extraction of benefits.)  As a final point of evidence, young growing vine tips too small to have been water conduits seem to follow the moss.     Personally, I think the vine uses the moss as a private rooting bed.

Tiny vine tips seem to follow moss.

Vine pulled free, holding on to moss (technically, liverwort).

What about the reverse:  the moss using the vine?  Again, it makes good sense.  How could water running down the vine not help the adjacent moss?  After all,  you can find examples of moss benefiting from water channels other than vine stems.   For instance, a fork in a tree can funnel a narrow stream of water down the trunk.  The moss likes those “streams.”   Similarly, there are places where a big epiphyte on the trunk, say Cardinal Airplant, catches water and then releases it as a drizzle, like a drippy sponge.   Today’s moss can flourish airplants.  Personally, I think the moss does use the vine as a private irrigation line.

Moss below tree fork.

So then, if this is all true in both directions (!), you have a remarkable situation of mutual facilitation.   I’m not suggesting that the two species have evolved to help each other—that would be “mutualism.”  But here we seem to have a win-win circumstance where two species seem to “luck into” each other, like a man with a pack of cigarettes, meeting a man with a book of matches.

Moss thriving below airplant drippage

Look how the vine “steers.”