A Lazarus Fern?

When I returned to Ground Zero a week after the two lines of twelve ferns were planted, in order to take the first set of time-lapse photos, I was shocked and delighted to discover a healthy fern which had not been planted by us.    Since sword ferns, we are told, will not reproduce under a closed forest canopy, I assume that this fern has come back from the dead:  enough life lingered in the rhizome for it to regrow after three years of inactivity.   Hence: the Lazarus Fern.   Definitive evidence for this claim - of regrowth rather than new growth - could come from removing soil and locating (or not locating) a large rhizome; young ferns do not acquire a rhizome for at least five years.    I do not want to disturb this rare, resuscitated, old survivor - or is it a new young plant? - not yet.

Based upon the size of the seven fronds, and the time of year, these fronds must have been 2017 growth.   I did not notice this frond last year.  This is puzzling, but not completely unlikely:  inasmuch as  I did not expect to see any fern regrowth,  I may well have overlooked this one instance.

There are a few other rather straggly ferns surviving at ground zero.  They are all - except for this fern, and one other I will describe in a moment - found very close to the trail or to large trees.   All of these survivors are failing, and fewer of them are found with each passing year.   Perhaps some sort of micro-site effects, or interspecies cooperativity, is responsible for their imperfect survival. 

The other healthy fern found at ground zero is one of the two nursery ferns we planted in November 2014, at the suggestion of Jillian Weed, parks plant ecologist.   I watered both ferns through the first two summers; one has survived:

This survivor, and the surprising regrowth of the Lazarus Fern suggests a possibility: that the putative pathogen killing the ferns,  which spreads at the rate of about 30 meters a year, may now be absent from ground zero.    Perhaps something in the genetic makeup of the Lazarus Fern, or its micro-site, of some unknown factor - some apparently unique factor/s allowed it to regrow.   The survival of one of the two 2014 plantings is consistent with this hypothesis:  whatever kills the ferns now appears to be gone.    This may be a cause for optimism - or it may be that the killing agent will return and once again attack ferns at ground zero if the ferns are re-established.  

For now, I will take comfort in the possibility that the scourge has moved on, and that at least one native plant is resistant.   We will collect spores from the Lazarus Fern in July and raise up a bunch of baby ferns,  which will also possibly be resistant, for further experimental planting.   If this is a genetic trait, and if it has high penetrance, we may have stumbled upon a partial remedy for the sword fern die-off.